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[edit] Creationism

• Science consists of adherence to the scientific method. This requires that theories be empirically testable.
• Theories of macroevolution, archaeology, and historical geology are fundamentally different from theories of chemistry, physics, or empirical geology, because they are theories of past events. Because the events being studied occured in the past, they cannot be empirically repeated, tested, or verified, and cannot make falsifiable predictions. While theories in the latter category may be experimentally tested and observed (for instance, the structure of DNA or the operation of microevolution), theories in the former category cannot be empirically tested, and are therefore subject to historical evidence, human interpretation, or faith.
• For instance, theories about the alleged evolutionary pathway for the eye cannot be empirically tested, because it is supposed to have occured long in the past, and by radically different pathways in insects, fish, and mammals, whose eye structures are significantly different. Scientists can only hypothesize about how the eye could have evolved, but they cannot say with scientific certainty that it did occur, or how.
• Similarly, the events of creation and the flood may be inferred from the evidence, but may not be stated with any degree of scientific certainty, because they cannot be repeated or tested.
• Creationists believe that the findings of empirical science most strongly support the creationist viewpoint.
• Creationists argue that faith and science are not only consistent but dependent upon each other for coherence, and that science and the universe can only be properly understood when seen in light of their Creator. They argue that many scientific innovators (including Aristotle, Gallileo, Newton, and Einstein), while highly critical of the organized religion of their day, also found belief in a Creator of one form or another to be the most reasonable explanation for the nature of things. While this is not evidence or proof of the existence of a creator, it is evidence that in the opinion of many of the finest scientific minds in history, faith and science are both consistent and interdependent.
• Creationists argue that modern science arose within the context of Christianity, due to its emphasis on unity, causality, and reality, all of which stem from belief in a Creator. While science is not dependent on any particular creed, it cannot function properly without acknowledging the Creator.

[edit] Mainstream science

• Science consists of adherence to the Scientific method. This requires that theories be empirically testable.
• It is disingenuous to insist that evolution as a whole be repeatable, since on this argument creationism, which is also not repeatable, would also not count as science.
• Some sciences, because of the nature of their subject, are called historical sciences. These include Astronomy, Geology, Archaeology and Evolutionary Biology. As with all sciences, theories in each of these sciences are empirically tested against the existing physical evidence, and are expected to be able to make verifiable or falsifiable predictions about future discoveries.
• There is no such thing as scientific certainty. Science consists of theories that are judged against the empirical evidence, but any and every scientific theory might be false. It is a misunderstanding of the basic principles of science to claim that the fact that a theory might be wrong counts against it.
• Theories about Abiogenesis and Macroevolution are tested against the existing evidence. These tests are repeatable, observable processes.
• Mainstream scientists assert that there is no logical difference between testing a theory about macroevolution, and testing a theory about the interaction of molecules in a test tube. The interactions of molecules in a test tube are not observed directly, but inferred from other observations. In exactly the same way, in Macroevolution the events took place in the past, and so are not directly observable, but may be inferred from fossil evidence. In both cases theories about unobservable phenomena are tested using observable phenomena. Mainstream scientists assert that accepting the creationist argument would mean rejecting Chemistry as unscientific.
• Isaac Newton studied alchemy, but that does not make alchemy scientific. That some scientists are or were Christian is asserted by mainstream scientists to have no relevance to the issue of whether creationism is scientific. Mainstream scientists also assert that this creationist argument is an example of the fallacy ad hominem circumstantial
• Mainstream science does not object to faith forming a part of a scientist’s worldview. It does object to faith forming a part of scientific explanations.
• Mainstream scientists assert that modern science has a multicultural history, and simply is not dependent on any particular religious perspective. Although individual scientists may have faith, mainstream scientists assert that science forms a world view that is independent of religious belief.

[edit] Creationism

The creationist model of geology is Flood geology, and is defined by the story of Noah's Ark, as reported in Genesis. Most major geological formations are explained in terms of a global flood which, according to the Ussher-Lightfoot Calendar, occured approximately 4,500 years ago, destroying all animal life on the planet with the exception of the animals and people preserved in the ark, and having a serious impact on Earth's geology.

[edit] Mainstream science

The mainstream model of geology is defined by the principle of Uniformitarianism, that is, the idea that geological phenomena are the result of gradual geological processes which took place over billions of years. As presented by creationists, flood geology violates the laws of physics. Most flood models deal with the water after the flood by proposing that it became our present oceans. In order to change the density and/or temperature of at least a quarter of the earth's crust fast enough to raise and lower the ocean floor in a matter of months would require mechanisms beyond any proposed in any of the flood models, and would violate basic fluid equations without massive energy transformations.

[edit] Old Earth Creationism

• Based on Uniformitarianism and Radiometric dating, holds that the first chapter of Genesis is a metaphor and the Earth may be billions of years old, as estimated by Radiometric dating. In some cases, events subsequent to the first chapter of Genesis are held to have occurred in the timeframe indicated by the Genealogies of Genesis.

[edit] Young Earth Creationism

• Based on the Genealogies of Genesis, most Young Earth Creationists hold that the earth is approximately 6,000 years old (although some have allowed for up to 10,000, but support for this is dwindling). Methods of Radiometric dating (see section below) and Ice core analysis are rejected due to their uniformitarian assumptions, such as the level of radiation in the original rocks and the rate of ice accrual, respectively.
• Assumptions of a naturalistic origin for the Earth and the solar system are rejected, because currently models for these processes are inadequate, and due to things such as the chaos effect, extrapolation into the distant past is mere speculation.

[edit] Mainstream science

• Many meteorites have been dated using Isochron dating. For a significant number of these the date is found to be more than 4 billion years ago.
• The oldest minerals found on earth are zircons from Western Australia. Using the uranium-lead dating method cristallisation ages up to 4.404 billion years were determined, giving a lower limit of the age of the earth.
• Radioactive dating, inferred from nuclear physicists' measurements, says: 4,600,000,000 years. See the article Age of the Earth.
• On the basis of analyses using chemical and physical techniques, Ice cores provide an estimate for the earth's age exceeding 720,000 years (This method depends on some uniformity in snow fall). Seasonal variations in temperature allow the estimate of time period covered by an ice core to be performed by the equivalent of counting tree rings (to determine the age of a tree). This method does not depend on the rate of snowfall. Seasonal variations get harder to pick out as the layers get thinner but even at depths corresponding to 30,000 years ago the layers can be 3 mm thick and indeed more than 30,000 seasonal layers can be observed (See Wise D. 1998).
• The ratio of hydrogen to helium inside the sun together with the rate of fusion in the sun is used to estimate the sun's age at 5 billion years. Models predict planet formation within a few million years.
• Extrapolations back in time in the solar system do not allow us to predict the moon's position 5 billion years ago because of chaos theory.
• Current models of planetary formation have flaws. This can be explained by the fact that the computational complexity of simulating planetary formation is very high. To the accuracy with which we can simulate planet formation general relativity is in agreement with the facts.
• Fossils of coral from lower sedimentary layers show growth bands that indicate that when they were growing there were significantly more than 365 days in a year. This agrees with the predictions of the length of day of the earth in the period when paleontologists say the coral grew. [1]

[edit] Creationism

• Young earth creationists believe that some geological phenomena are a result of the original creation of the earth, others are a result of a worldwide flood (Flood geology) and yet others are a result of the geological forces observable today.
• Young earth creationists believe that, for example, the folding of rock layers can be better explained by the folding taking place whilst the layers were still soft following rapid deposition, and before they hardened.
• Flood geology holds that a global flood can explain the following phenomena more parsimoniously than uniformitarian geology:
  • Submarine canyon extensions on the major world rivers as runoff after the flood when sealevels were made lower due to the dropping seabed and rising mountains.
  • Massive-scale layered fossilization as animals would sinking to the level of their relative densities in the liquefaction accompanying the flood.
  • Fossil fuel deposits as dead plant and animal matter buried under sediments during a worldwide flood. Creationists hold that mainstream theories of fossil fuel formation are inadequate.
  • Creationists claim that deep limestone deposits (such as those observed on the white cliffs of Dover, UK, and Normandy France, which are between 600-1000ft deep and extend under the channel, or the Bahamas Bank, where limestone extends almost 6 miles), are most reasonably explained as rapidly precipitating when CO2 suddenly escapes from carbonate-saturated ground water, as has been observed today on many Carribean islands.
    • Flood geologists claim that uniformitarian explanations for the formation of limestone fail because:
      • The slow accretion of limestone over millenia predicts a great deal of mixing with other minerals and compounds within the deposit, which is not observed in major limestone deposits.
      • The prevailing model of limestone deposition among mainstream scientists is that limestone accumulates in shallow seas. Creationist assert that this cannot explain the existence of the Bahamas Bank limestone deposit. Creationists assert that the formation of the deposit would require the sea to have been 6 miles deep at the time of limestone formation (under which conditions limestone does not form) or for the sea floor to have shifted under the sedimentary weight.
  • Flood geologists conclude that limestone formation is best understood as occuring during catastrophic geological activity consistent with a global flood.

[edit] Mainstream science

• The geological features we see today are the result of the same processes that we observe today. The generally accepted rationale for this is Occam's razor. See the article on the uniformitarianism.
  • For example, the folding of rock layers can be accounted for by the forces compressing the rocks very slowly over long periods of time. The layers being soft is not a bonus since they would slide and not look like they do.
• Flood geology does not agree with the facts in the following ways:
  • There are places where there are no traces of floods but continuous addition of strata.
  • Flood geology does not adequately explain the sorting of fossils - mammals and flowering plants in the higher strata only, trilobites and dinosaurs in the lower strata only.
• Mainstream scientists assert that the following statements are biologically highly improbable but are implied by young earth creationism:
  • For the 150 meter thick Kaibab Limestone to have been deposited during the Flood year, the lime secreting organisms would have had to have been forming carbonate at the rate of 80 cm/day.
  • The El Capitan Reef in Texas would have had to grow at a rate of 7cm/hour or 80,000 times the current growth rates.
  • There are 1.16x10¹³ metric tons of coal reserves, and at least 100 times that much unrecoverable organic matter in sediments. A typical forest, even if it covered the entire earth, could supply only 1.9x10¹³ metric tons of coal upon conversion. Hence the origin of coal from organic matter during a worldwide flood is unlikely.
• The following flood geology models do not make sense and have fundamental problems with basic physics: vapor canopy, comet, hydroplate and runaway subduction.

[edit] Creationism

• Carbon-14 dating is generally accepted as reliable in most cases, and carbon dating efforts result in ages within a timescale consistent with creation.
• Radiometric dating of rocks (such as K/Ar) is unreliable due to its assumption that there was none of the daughter isotope present when the original rock was formed. The presence of any of the daughter isotope in the rock when the rock forms will cause radiometric dating methods to give ages far higher than the actual age of the rock.
• In particular, the K/Ar method has been shown to be unreliable in at least 20% of lava rock samples and at least one diamond sample, due to excess Argon in the sample which give ages far older than the known and observed age of the rock. Published articles in Science have inferred that this is caused by excess argon in mantle fluids, and creationists believe these data render K/Ar dating methods utterly meaningless. [2]
• Radiometric dates of strata are regularly "calibrated" to the "known" age of the evolution of a particular organism found in the strata, which is in turn "dated" by the unreliable radiometric methods described above. Due to this circular reasoning and calibration, neither methodology is the slightest bit reliable.
• The differences in radioisotopes at different depths could be due to any number of causes, not the least of which is that more excess argon was released early in the flood than later, resulting in more distorted readings at greater depths.
• Isochron methods are also rejected, because "When the isochron data are the result of the rock being a blend of two original species, the diagram is called a mixing line, having no time significance. All whole-rock isochrons are necessarily mixing lines. Since only whole-rock isochrons play a significant role in the dating game, isotopic geochronology can be rather generally discredited." [3]
• Radiometric dating of crystals in excess of 6,000 years is not inconsistent with some forms of Creationism, which hold that the events recorded were only God's preparation of a pre-existing Earth for life, since in the text, before God created anything, his "spirit moved over the waters," implying that the Earth itself predates Genesis 1.

[edit] Mainstream science

• Independent measurements, using different and independent radiometric techniques, give consistent results [Meert 2000; Dalrymple 2000; Lindsay 1999].
• Radiometric dating is consistent with Milankovitch cycles, which depend only on astronomical factors such as precession of the earth's tilt and orbital eccentricity [Hilgen et al. 1997].
• Radiometric dating is consistent with the luminescence dating method [Thorne et al. 1999; Thompson n.d.].
• Radiometric dating gives results consistent with relative dating methods such as "deeper is older." [Lindsay 2000]
• Coral clocks are consistent with radiometric dating (when gravity drag is taken into account). See [4]
• Using Isochron dating there is no need to assume that no daughter isotope was present when the rock was formed, because one gets the amount of the daughter isotope which were present at the time of rock-formation as a result of the determined isochron and can use this information to calculate reliable ages.
• To calibrate radiometric methods only the decay constants of radionuclids are needed. Decay constants can be determined in laboratory e.g. by measuring the radioactivity of an given amount of an radionuclid. For instance the decay constants of uranium isotopes, used for uranium lead dating, are known with very high precision because they are also needed for the construction of nucler power plants. There is no circular reasoning in calibration of radiometric dating.
• If all determined samples of a dated rock are fitting the determined isochron a disturbance of the used isotopic system after rock formation, e.g. by diffusion, can be excluded and the determined age is reliable. Also a "mixing line" instead of an isochron can be excluded because in general the data for different mineral fractions of an rock do in case of an mixing event not correlate very well and thus do not lie on a straight line. This is valid for whole rock isochrons as well as for mineral isochrons and both of them can be (and are often) used for radiometric dating.
• Since Argon is a noble gas and escapes easily from rocks the K-Ar method often gives too low (and not too high) ages if they are determined by simply measuring the Kalium and Argon concentrations of an rock. However, usually the more sophisticated 39Ar-40Ar measuring technique is applied which is capable to assure the reliability of an determined age by exluding that diffusion loss of Argon or an other event affected the K-Ar isotopic system after the formation of the rock.
• In the case of uranium-lead dating usually a Concordia-diagramm is used to exlude disturbation of the U-Pb isotopic system after the formation of the dated rock and to assure the reliability of an determined age.
• It is not necessary that whole rock isochrons and mineral isochrons are giving the same age, because it is possible (and often is the case) that they date different events in the history of rock formation (e.g. time of differentiation of precursor melt and time of cristallisation).

[edit] Creationism

• Geological strata on the east coast of the americas and the west coast of africa-europe match. This can be accounted for by catastrophic plate tectonics, which can also explain some aspects that creationists assert are difficult to explain by uniformitarian models, such as the "zebra-stripe" pattern of magnetic polarity reversals (in rocks near the mid-ocean ridges).
• Radiometric dating of geological formations is rejected, because creationists assert that radiometric dating depends entirely on assumptions of the level of radioactivity in the original rock, when the actual initial level of radiation in the rock is unknown. Creationists argue that because of these assumptions, radiometric dating methods are mere speculation.
• Creationists claim that uniformitarian plate tectonics lacks a plausible mechanism for its action, whereas catastrophic plate tectonics, it is hypothesised, is driven by runaway subduction of the oceanic plates under the continental plates.

[edit] Mainstream science

• Geological strata on the east coast of the americas and the west coast of africa-europe match. This can be accounted for by plate tectonics given billions of years for the movement, whilst Mainstream scientists assert that young earth creationism does not explain this.
• The geomagnetic dynamo at the Earth's core switches polarity over geologic times. Creationists apparently do not realize that this accounts for the observed differences in the magnetization of rocks.
• Catastrophic plate tectonics says that all ocean floors should be essentially the same age. But radiometric dating indicates that the age changes gradually, from brand new to tens of millions of years old.
• Island chains such as the Hawaiian Islands indicate that the ocean floor moved slowly over erupting "hot spots." Radiometric dating and relative states of erosion both indicate that the older islands are very much more than a year or so older, as catastrophic tectonics would require.
• Rapid plate tectonics lacks a plausible mechanism for its action. Also the enormous amounts of energy released would cause phenomena such as crustal deformation and atmospheric instability that are not observed to have occurred.

[edit] Creation science

• The Flood geology theory says: Fossil fuels are dead animal and plant matter from organisms that died during a global flood, approximately 4,500 years ago.

Prior to the flood, the Earth's environment was significantly more amenable to life than it is today, indicated by the presence of animals unable to survive in today's environment, such as the dinosaurs and enormous insects found in the fossil record, the global semi-tropical climate apparent in the fossil record, the reported human lifespans of 800 years or more, the absence of rain in favor of specially designed underground springs to water the Earth (as indicated in Genesis 2:5-6), superior soils which were washed away and rendered unrecoverable during the flood, and significantly more land-area than today (as the seas necessarily expanded significantly during and after the flood), allowing for more life on Earth than is possible under today's conditions.

The plants and animals died in the flood; the flood and associated violent geological activity tore sediments from the antediluvian Earth, and brought them into suspension in the flood waters. During and after the flood, some of the dead plant and animal matter was buried quickly beneath the sediments. When the sediments dried into rock strata, the dead matter was heated and pressurized. The organic molecules associated with these organisms formed a group of chemicals known as kerogens which were then transformed into hydrocarbons by the process of catagenesis, and transformed into present day fossil fuels.

• Radiometric dating methods are rejected. See appropriate section below.

• It is argued that the flood theory is superior because it provides a mechanism whereby large amounts of organic matter came to be buried in deep sedimentary rock before it decayed.

[edit] Mainstream science

• Biogenic theory: fossil fuels are the altered remnants of ancient plant and animal life deposited in sedimentary rocks.
• Abiogenic theory: hydrocarbon deposits are primordial, being part of the Earth as it formed.
• It is argued that the Flood theory fails because:
  • Radiometric dating methods date most fossils to ages measured in millions of years. See the section on radiometric dating methods.
  • One large fossil site on its own (the Karroo Formation in Africa) is estimated to contain 800 billion vertebrate fossils. This is less than 1% of the worlds fossils and so on the assumption that most fossils originated from a flood 6000 years ago there would have been 2100 vertebrate animals per acre, far more than we see today [Schadewald 1982].
  • There are 1.16x10¹³ metric tons of coal reserves, and at least 100 times that much unrecoverable organic matter in sediments. A typical forest, even if it covered the entire earth, could supply only 1.9x10¹³ metric tons of coal upon conversion. Hence the origin of coal from organic matter during a worldwide flood is unlikely.

[edit] Creationism

During the global flood, some of the plants and animals were buried in soft sediments that were laid down quickly during the flood. After the floodwaters receded, the sediments dried and hardened into sedimentary strata. Fossils are therefore the remains of animals that died during the global flood, approximately 4,500 years ago.

[edit] Mainstream science

Varves within the geologic column show seasonal layers over many, many years. In many cases, such as the Green River formation, these layers are too fine to have settled out in less than several weeks per layer. Varves in New England show evidence of climate change 17,500 to 13,500 years ago which matches climate patterns in other parts of the world. These layers prove that the geological record was not produced in just one event.

The geological eras and fossil records are consistent worldwide. The flood myth cannot explain the worldwide agreement between "apparent" geological eras and several different (independent) radiometric and nonradiometric dating methods. The fossil record is sorted in an evolutionary order, unlike what would be expected from a global flood scenario. Standard models explain the following pieces of evidence that flood geology fails in doing:

• the extremely good sorting observed.
• the relative positions of plants and other non-motile life. Modern plants do not appear low in the geologic column.
• some groups of organisms, such as mollusks, are found in many geologic strata.
• organisms (such as brachiopods) which are very similar hydrodynamically (all nearly the same size, shape, and weight) are still perfectly sorted.
• extinct animals which lived in the same niches as present animals didn't survive as well (for example, pterodons).
• coral reefs hundreds of feet thick and miles long are intact with other fossils below them.
• small organisms dominate the lower strata, whereas fluid mechanics says they would sink slower and thus end up in upper strata.
• artifacts such as footprints and burrows are also sorted.
• no human artifacts are found except in the very uppermost strata. If, at the time of the Flood, the earth was overpopulated by people with technology for shipbuilding, why were none of their tools or buildings mixed with trilobite or dinosaur fossils?
• different parts of the same organisms are sorted together. Pollen and spores are found in association with the trunks, leaves, branches, and roots produced by the same plants.
• ecological information is consistent within but not between layers. Fossil pollen is one of the more important indicators of different levels of strata. Each plant has different and distinct pollen, and, by telling which plants produced the fossil pollen, it is easy to see what the climate was like in different strata. Was the pollen hydraulically sorted by the flood water so that the climatic evidence is different for each layer?

[edit] Creationism

The loess was formed immediately following the flood. The rich soils of the antediluvian world were torn up in the flood, and redeposited as sediment. Due to rapid cooling at higher latitudes and the "great wind" described in Genesis 8:1, the still wet loess froze while being blown by the strong wind. The mammoths, trees, and other forms of life intact inside. In subsequent years, the ice melted, leading to the erosion of loess between hills.

The argument regarding paleosoils is rejected, because radiometric dating methods are rejected (see section below).

It is argued that the flood theory is superior, because:

• it can explain how loess came to form through the simultaneous formation and freezing of soils 300M deep under cold and windy conditions sufficient to freeze mammoths solid in ice, while leaving sufficient loess to allow for the great erosion observable in the Yellow River.

[edit] Mainstream science

The loes deposits are wind-blown sediments from the Ordos Desert, and the grain size of the loess decreases the further one gets from the desert. [Vandenberghe et al. 1997]

It is argued that the flood theory fails, because:

• The Loess Plateau includes paleosoils within it. These are buried fossil soils, some of which would require tens of thousands of years to form. [Kukla and An 1989; Liu et al. 1985]

• The Loess Plateau has a layer of loess more than 300 m thick. Loess is wind-blown sediment which would not occur during a global flood. The Loess Plateau occurs around the downwind edges of the Ordos Desert, its source of sediments, and the grain size of the loess decreases the further one gets from the desert. [Vandenberghe et al. 1997]

[edit] Creationism

During the flood, salt accompanying the release of subterranean water (the "fountains of the great deep") caused the flood waters to become supersatured with salt, and precipitated thick layers of salt on the seafloor. The salt was quickly buried by other, denser sediments, which remained soft. In some areas, the salt, which was less dense than the higher sediments, pushed up through higher layers, forming salt domes, in which the other sedimentary layers bent around the salt dome. Dead plant and animal matter that was buried beneath the denswer sediments rose to rest between the salt and rock strata, where it was converted into fossil fuels.

• It is argued that the flood theory is superior, because:
  • It can explain how salt layers came to be laid beneath other sediments (rapid sedimentation) without being mixed with the other sediments, while mainstream theories cannot (slow sedimentation onto the salt would dissolve the salt back into the sea);
  • It can explain how fossil fuels came to form between the salt and rock strata, while mainstream theories cannot explain how petroleum came to collect;
  • It can explain how salt domes came to form in areas where there is no evidence that seas were ever cut off from other seas to form the salt pans.
  • It can explain how the salt came to push through the denser sediments, because the sediments were still wet, whereas the mainstream theory requires that the salt pushed its way through solid rock, a phenomena which is neither observed nor explainable.

[edit] Mainstream science

The salt that forms these deposits was laid down in prehistoric times, mainly in places where inland seas were periodically connected and disconnected from oceans. As these seas are cut off from the main body of water, the water evaporates, leaving immense salt pans. Over time, the salt is covered with sediment and becomes buried. The salt pushed to the surface through sedimentary layers that had already hardened into solid rock, forming large bulbous domes, sheets, pillars and other structures as it rose. The strata imediately above the dome that are not penetrated are pushed upward, creating a dome-like reservoir above the salt where petroleum can gather.

How could the Flood deposit layers of solid salt? Such layers are sometimes meters in width, interbedded with sediments containing marine fossils. This apparently occurs when a body of salt water has its fresh-water intake cut off, and then evaporates. These layers can occur more or less at random times in the geological history, and have characteristic fossils on either side. Therefore, if the fossils were themselves laid down during a catastrophic flood, there are, it seems, only two choices: (1) the salt layers were themselves laid down at the same time, during the heavy rains that began the flooding, or (2) the salt is a later intrusion. I suspect that both will prove insuperable difficulties for a theory of flood deposition of the geologic column and its fossils. [Jackson et al, 1990]

[edit] Creationism

During the flood, carbonate-saturated groundwater was released from subterranean water-sources ("the fountains of the great deep") under great pressure. When the water reached the surface, the pressure on the water dropped, and calcium carbonate (or limestone) was released from solution, and quickly precipitated and cemented, forming pure, white limestone deposits. It is argued that the flood explanation is superior, because:

• It can explain how limestone deposits (both pure and impure) came to be relatively free of mixing with other minerals, as would be expected if the deposits were slowly accumulated over millions of years.
• It can explain the formation of the Bahamas Bank limestone deposit, which is six miles deep. The prevailing theory of limestone formation, that of slow accretion, requires that the sea be relatively shallow, because pH drops with sea depth, which dissolves limestone. In order for the limestone to form gradually, therefore, the seabed must have slowly dropped six miles in order to allow the limestone to form in a shallow sea, and no plausible mechanism has been provided for this.

[edit] Mainstream science

Limestone developed from the slow accumulation of limestone-secreting organisms over millenia.

Uniformitarian processes explain limestone formations far better than catastrophism does.

• Limestones form continuously today over wide areas (such as the Caribbean) as calcium carbonate is precipitated from water directly and through the actions of organisms. Limestone formation easily fits within conventional geology.
• Limestones appear in strata interleaved between strata of sandstones and other rocks. A single event could not explain all the layers.
• Limestones often include fragile fossils that could not survive catastrophic transport.

Dolomites require no exceptional explanation. They form via diagenesis (a sort of chemical rearrangement in the deep subsurface) from calcite, the main ingredient of limestone. Creationism does not explain the origin of dolomite.

There are roughly 5 x 10²³ grams of limestone in the earth's sediments [Poldervaart, 1955], and the formation of calcite releases about 11,290 joules/gram [Weast, 1974, p. D63]. If only 10% of the limestone were formed during the Flood, the 5.6 x 10²⁶ joules of heat released would be enough to boil the flood waters.

How were limestone deposits formed? Much limestone is made of the skeletons of microscopic sea animals. Some deposits are thousands of meters thick. Were all those animals alive when the Flood started? If not, how can creationists reasonably explain the well-ordered sequence of fossils in the deposits? Roughly 1.5 x 10¹⁵ grams of calcium carbonate are deposited on the ocean floor each year. [Poldervaart, 1955] A deposition rate ten times as high for 5000 years before the Flood would still only account for less than 0.02% of limestone deposits.

[edit] Creationism

Creationist biology is based on the idea that God created all life on the planet in a finite number of discrete forms, commonly called "kinds," which had the ability to vary significantly within their kind, but cannot arise spontaneously, and cannot change from one kind into another. As such, creationists ascribe to the law of biogenesis, that is, the idea that life can only come from life, as well as the idea of Irreducible complexity, that is, that life is designed with intricate and interconnected components for a purpose, rather than merely the result of variation and selection. Creationists believe that 7 pairs of each "clean" animal and 2 pairs of each "unclean" animal were taken onboard the ark during the flood, and that current species diversity is the result of mutation, variation, natural selection, and genetic drift following the release of the animals from the ark.

[edit] Mainstream science

Mainstream biology is defined by the idea of evolution, that is, that life develops from less diversity and less complexity to more diversity and more complexity through the process of variation (by means of genetic mutation and recombination), natural selection, and genetic drift. Consequently, they believe that all life on the planet shares a common ancestor.

Irreducible complexity can evolve. It is defined as a system which loses its function if any one part is removed, so it only indicates that the system did not evolve by the addition of single parts with no change in function. That still leaves several evolutionary mechanisms:

• Deletion of parts.
• Addition of multiple parts; for example, duplication of much or all of the system [Pennisi 2001].
• Change of function.
• Addition of a second function to a part [Aharoni et al. 2004].
• Gradual modification of parts.

All of these mechanisms have been observed in genetic mutations. In particular, deletions and gene duplications are fairly common [Lynch and Conery 2000; Hooper and Berg 2003; Dujon et al. 2004], and together they make irreducible complexity not only possible, but expected. In fact, it was predicted as early as 1939 [Muller 1939].

Evolutionary origins of some irreducibly complex systems have been described in some detail. For example, the evolution of the Krebs citric acid cycle has been well studied; irreducibility was no obstacle to its formation [Meléndez-Hevia et al. 1996].

Irreducible complexity is poorly defined. It is defined in terms of parts, but it is far from obvious what a "part" is. Logically, the parts should be individual atoms, because they are the level of organization which does not get subdivided further in biochemistry, and they are the smallest level which biochemists consider in their analysis. Behe, however, considers sets of molecules to be individual parts, and he gives no indication of how he makes his determinations.

Moreover, systems which have been considered irreducibly complex might not be. The mousetrap which Behe uses as an example of irreducible complexity can be simplified by bending the holding arm slightly and removing the latch. The bacterial flagellum is not irreducibly complex because it can lose many parts and still function, either as a simpler flagellum or a secretion system. Many proteins of the eukaryotic flagellum (also called a cilium or undulipodium) are known to be dispensable, because functional swimming flagella are known which lack these proteins. In spite of the complexity of Behe's protein transport example, there are other proteins for which no transport is necessary [ref. in Ussery 1999]. The immune system example which Behe includes is not irreducibly complex because the antibodies which mark invading cells for destruction might themselves hinder the function of those cells, allowing the system to function (albeit not as well) without the destroyer molecules of the complement system.

[edit] Creationism

• Young Earth Creationism says: Various kinds (reproductively separate) of living organisms were created 6,000 years ago. These kinds differentiated via sexual reproduction and information-losing mutations combined with natural selection to form the current biological diversity.
• Creationists claim the fossil record shows many existing and extinct creatures, but no continuum of intermediate forms between different kinds.
• Phylogenetic trees are rejected as evidence of common ancestry because, creationists claim, the data are meaningless until most-parsimonious tree algorithms are applied, and most-parsimonious tree algorithms assume common ancestry.
  • Further, phylogenetic tree data are entirely dependent on which algorithm is used -- most typically most-parsimonious or maximum-likelihood. The use of a different algorithm produces a different tree, and no algorithm is inherently superior to any other. As a result, it is no surprise that different genes reveal similar trees, when the same algorithm is applied.
• The near-universality of the genetic code and similarity of genes and organs in living things are predicted by creation as a design which was used on multiple forms of life because it was an effective design.
• Young Earth Creationists assert that there are incidents of irreducible complexity and that these can only be explained by their creation by an intelligent designer.
• Speciation is predicted by creationism, and is observed by science. But all such speciation is said to involve a rearrangement or reduction in genetic information, and no creation of new genetic information.

[edit] Mainstream science

• Mainstream scientists assert that comparison of the fossil record gives evidence that many of today's species have common ancestors. See the article on fossils
• Mainstream scientists contend that when you have only a few fossil remains of a greatly branching tree of species you do not expect to see a continuum of forms. On the other hand when you have a large number of fossils then you do expect to see this [5]
• Several fossils have been found [6] that mainstream scientists believe are intermediate forms.
• Common ancestry predicts that the comparisons of several genes from various species would show similar phylogenetic trees. Mainstream scientists assert that this is in fact the case and is therefore evidence for common ancestry. See the article on phylogenetic trees.
  • The assumption of common ancestry is necessary to obtain meaningful phylogenetic trees however if there were no common ancestry for life on earth then phylogenetic trees derived from different genes would not be expected to be similar.
• The near universality of the genetic code is predicted by evolution.
• Speciation events have been observed in plants (mainly due to polyploidy).
• Speciation events have been induced by selective breeding and reproductive isolation in many insects most notably in drosophila.

Creationist sometimes ask why there is such a seeming lack of interest in reporting observations of speciation events.

Four things account for this lack of interest. First, it appears that the biological community considers this a settled question. Many researchers feel that there are already ample reports in the literature. Second, most biologists accept the idea that speciation takes a long time (relative to human life spans). Because of this we would not expect to see many speciation events actually occur. The literature has many more examples where a speciation event has been inferred from evidence than it has examples where the event is seen. This is what we would expect if speciation takes a long time. Third, the literature contains many instances where a speciation event has been inferred. The number and quality of these cases may be evidence enough to convince most workers that speciation does occur. Finally, most of the current interest in speciation concerns theoretical issues. Most biologists are convinced that speciation occurs. What they want to know is how it occurs. One recent book on speciation (Otte and Endler 1989) has few example of observed speciation, but a lot of discussion of theory and mechanisms.

Most of the reports, especially the recent reports, can be found in papers that describe experimental tests of hypotheses related to speciation. Usually these experiments focus on questions related to mechanisms of speciation. Examples of these questions include:

Does speciation precede or follow adaptation to local ecological conditions? Is speciation a by-product of genetic divergence among populations or does it occur directly by natural selection through lower fitness of hybrids? How quickly does speciation occur? What roles do bottlenecks and genetic drift play in speciation? Can speciation occur sympatrically (i.e. can two or more lineages diverge while they are intermingled in the same place) or must the populations be separated in space or time? What roles do pleiotropy and genetic hitchhiking play in speciation? It is important to note that a common theme running through these questions is that they all attempt to address the issue of how speciation occurs.

What evidence is necessary to show that a change produced in a population of organisms constitutes a speciation event? The answer to this question will depend on which species definition applies to the organisms involved.

One advantage of the BSC is that it provides a reasonably unambiguous test that can be applied to possible speciation events. Recall that under the BSC species are defined as being reproductively isolated from other species. Demonstrating that a population is reproductively isolated (in a nontrivial way) from populations that it was formerly able to interbreed with shows that speciation has occurred. In practice, it is also necessary to show that at least one isolating mechanism with a hereditary basis is present. After all, just because a pair of critters don't breed during an experiment doesn't mean they can't breed or even that they won't breed. Debates about whether a speciation event has occurred often turn on whether isolating mechanisms have been produced.

Mechanisms which produce reproductive isolation fall into two broad categories -- premating mechanisms and postmating mechanisms.

Premating isolating mechanisms operate to keep species separate before mating occurs. Often they act to prevent mating altogether. Examples of premating mechanisms include ecological, temporal, behavioral and mechanical mechanisms.

Ecological isolation occurs when species occupy or breed in different habitats. It is important to be careful when claiming ecological isolation. For example, I have a population of Dinobryon cylindricum (a colonial algal flagellate) growing in a culture tube in an environmental chamber. It's been there for three years (which is a lot of time in flagellate years! :-)). Even though there is no possibility that they will mate with the D. cylindricum in Lake Michigan, it would be silly to assert that they therefore constitute a separate species. Physical isolation alone does not constitute an isolating mechanism with an hereditary basis.

Temporal isolation occurs when species breed at different times. This may be different times of the year or different times of day.

Behavioral isolating mechanisms rely on organisms making a choice of whether to mate and a choice of who to mate with. Differences in courtship behavior, for instance, may be sufficient to prevent mating from occurring. A behavioral isolating mechanism should result in some sort of positive assortative mating. Simply put, positive assortative mating occurs when organisms that differ in some way tend to mate with organism that are like themselves. For example, if blonds mate exclusively with blonds, brunettes mate exclusively with brunettes, redheads mate exclusively with redheads (and those of us without much hair don't get to mate :-() the human population would exhibit a high degree of positive assortative mating. In most examples in the literature when positive assortative mating is seen it is not this strong. Positive assortative mating is especially important in discussions of sympatric speciation.

Mechanical isolating mechanisms occur when morphological or physiological differences prevent normal mating.

Postmating isolating mechanisms prevent hybrid offspring from developing or breeding when mating does occur. There are also several examples of postmating mechanisms.

Mechanical postmating isolating mechanisms occur in those cases where mating is possible, but the gametes are unable to reach each other or to fuse. Mortality acts as an isolating mechanism when the hybrid dies prior to maturity. Sterility of hybrids can act as an isolating mechanism. Finally a reduction in the fitness of the hybrid offspring can isolate two populations. This happens when the F1 hybrid is fertile but the F2 hybrid has lower fitness than either of the parental species.

There is no unambiguous criterion for determining that a speciation event has occurred in those cases where the BSC does not apply. This is especially true for obligately asexual organisms. Usually phenetic (e.g. phenotypic and genetic) differences between populations are used to justify a claim of speciation. A few caveats are germane to this. It is not obvious how much change is necessary to claim that a population has speciated. In my humble opinion, the difference between the "new species" and its "ancestor" should be at least as great as the differences among recognized species in the group (i.e. genus, family) involved. The investigator should show that the change is persistent. Finally, many organisms have life cycles/life histories that involve alternative morphologies and/or an ability to adjust their phenotypes in response to short term changes in ecological conditions. The investigator should be sure to rule these things out before claiming that a phenetic change constitutes a speciation event.

The following are several examples of observations of speciation.

• While studying the genetics of the evening primrose, Oenothera lamarckiana, de Vries (1905) found an unusual variant among his plants. O. lamarckiana has a chromosome number of 2N = 14. The variant had a chromosome number of 2N = 28. He found that he was unable to breed this variant with O. lamarckiana. He named this new species O. gigas.

• Digby (1912) crossed the primrose species Primula verticillata and P. floribunda to produce a sterile hybrid. Polyploidization occurred in a few of these plants to produce fertile offspring. The new species was named P. kewensis. Newton and Pellew (1929) note that spontaneous hybrids of P. verticillata and P. floribunda set tetraploid seed on at least three occasions. These happened in 1905, 1923 and 1926.

• Owenby (1950) demonstrated that two species in this genus were produced by polyploidization from hybrids. He showed that Tragopogon miscellus found in a colony in Moscow, Idaho was produced by hybridization of T. dubius and T. pratensis. He also showed that T. mirus found in a colony near Pullman, Washington was produced by hybridization of T. dubius and T. porrifolius. Evidence from chloroplast DNA suggests that T. mirus has originated independently by hybridization in eastern Washington and western Idaho at least three times (Soltis and Soltis 1989). The same study also shows multiple origins for T. micellus.

• The Russian cytologist Karpchenko (1927, 1928) crossed the radish, Raphanus sativus, with the cabbage, Brassica oleracea. Despite the fact that the plants were in different genera, he got a sterile hybrid. Some unreduced gametes were formed in the hybrids. This allowed for the production of seed. Plants grown from the seeds were interfertile with each other. They were not interfertile with either parental species. Unfortunately the new plant (genus Raphanobrassica) had the foliage of a radish and the root of a cabbage.

• A species of hemp nettle, Galeopsis tetrahit, was hypothesized to be the result of a natural hybridization of two other species, G. pubescens and G. speciosa (Muntzing 1932). The two species were crossed. The hybrids matched G. tetrahit in both visible features and chromosome morphology.

• Along similar lines, Clausen et al. (1945) hypothesized that Madia citrigracilis was a hexaploid hybrid of M. gracilis and M. citriodora As evidence they noted that the species have gametic chromosome numbers of n = 24, 16 and 8 respectively. Crossing M. gracilis and M. citriodora resulted in a highly sterile triploid with n = 24. The chromosomes formed almost no bivalents during meiosis. Artificially doubling the chromosome number using colchecine produced a hexaploid hybrid which closely resembled M. citrigracilis and was fertile.

• Frandsen (1943, 1947) was able to do this same sort of recreation of species in the genus Brassica (cabbage, etc.). His experiments showed that B. carinata (n = 17) may be recreated by hybridizing B. nigra (n = 8) and B. oleracea, B. juncea (n = 18) may be recreated by hybridizing B. nigra and B. campestris (n = 10), and B. napus (n = 19) may be recreated by hybridizing B. oleracea and B. campestris.

• Rabe and Haufler (1992) found a naturally occurring diploid sporophyte of maidenhair fern which produced unreduced (2N) spores. These spores resulted from a failure of the paired chromosomes to dissociate during the first division of meiosis. The spores germinated normally and grew into diploid gametophytes. These did not appear to produce antheridia. Nonetheless, a subsequent generation of tetraploid sporophytes was produced. When grown in the lab, the tetraploid sporophytes appear to be less vigorous than the normal diploid sporophytes. The 4N individuals were found near Baldwin City, Kansas.

• Woodsia abbeae was described as a hybrid of W. cathcariana and W. ilvensis (Butters 1941). Plants of this hybrid normally produce abortive sporangia containing inviable spores. In 1944 Butters found a W. abbeae plant near Grand Portage, Minn. that had one fertile frond (Butters and Tryon 1948). The apical portion of this frond had fertile sporangia. Spores from this frond germinated and grew into prothallia. About six months after germination sporophytes were produced. They survived for about one year. Based on cytological evidence, Butters and Tryon concluded that the frond that produced the viable spores had gone tetraploid. They made no statement as to whether the sporophytes grown produced viable spores.

• Speciation through hybridization and/or polyploidy has long been considered much less important in animals than in plants [[[refs.]]]. A number of reviews suggest that this view may be mistaken. (Lokki and Saura 1980; Bullini and Nascetti 1990; Vrijenhoek 1994). Bullini and Nasceti (1990) review chromosomal and genetic evidence that suggest that speciation through hybridization may occur in a number of insect species, including walking sticks, grasshoppers, blackflies and cucurlionid beetles. Lokki and Saura (1980) discuss the role of polyploidy in insect evolution. Vrijenhoek (1994) reviews the literature on parthenogenesis and hybridogenesis in fish. I will tackle this topic in greater depth in the next version of this document.

• Gottlieb (1973) documented the speciation of Stephanomeira malheurensis. He found a single small population (< 250 plants) among a much larger population (> 25,000 plants) of S. exigua in Harney Co., Oregon. Both species are diploid and have the same number of chromosomes (N = 8). S. exigua is an obligate outcrosser exhibiting sporophytic self-incompatibility. S. malheurensis exhibits no self-incompatibility and self-pollinates. Though the two species look very similar, Gottlieb was able to document morphological differences in five characters plus chromosomal differences. F1 hybrids between the species produces only 50% of the seeds and 24% of the pollen that conspecific crosses produced. F2 hybrids showed various developmental abnormalities.

• Pasterniani (1969) produced almost complete reproductive isolation between two varieties of maize. The varieties were distinguishable by seed color, white versus yellow. Other genetic markers allowed him to identify hybrids. The two varieties were planted in a common field. Any plant's nearest neighbors were always plants of the other strain. Selection was applied against hybridization by using only those ears of corn that showed a low degree of hybridization as the source of the next years seed. Only parental type kernels from these ears were planted. The strength of selection was increased each year. In the first year, only ears with less than 30% intercrossed seed were used. In the fifth year, only ears with less than 1% intercrossed seed were used. After five years the average percentage of intercrossed matings dropped from 35.8% to 4.9% in the white strain and from 46.7% to 3.4% in the yellow strain.

• At reasonably low concentrations, copper is toxic to many plant species. Several plants have been seen to develop a tolerance to this metal (Macnair 1981). Macnair and Christie (1983) used this to examine the genetic basis of a postmating isolating mechanism in yellow monkey flower. When they crossed plants from the copper tolerant "Copperopolis" population with plants from the nontolerant "Cerig" population, they found that many of the hybrids were inviable. During early growth, just after the four leaf stage, the leaves of many of the hybrids turned yellow and became necrotic. Death followed this. This was seen only in hybrids between the two populations. Through mapping studies, the authors were able to show that the copper tolerance gene and the gene responsible for hybrid inviability were either the same gene or were very tightly linked. These results suggest that reproductive isolation may require changes in only a small number of genes.

• Fruit Flies

• • Dobzhansky and Pavlovsky (1971) reported a speciation event that occurred in a laboratory culture of Drosophila paulistorum sometime between 1958 and 1963. The culture was descended from a single inseminated female that was captured in the Llanos of Colombia. In 1958 this strain produced fertile hybrids when crossed with conspecifics of different strains from Orinocan. From 1963 onward crosses with Orinocan strains produced only sterile males. Initially no assortative mating or behavioral isolation was seen between the Llanos strain and the Orinocan strains. Later on Dobzhansky produced assortative mating (Dobzhansky 1972).

• • Thoday and Gibson (1962) established a population of Drosophila melanogaster from four gravid females. They applied selection on this population for flies with the highest and lowest numbers of sternoplural chaetae (hairs). In each generation, eight flies with high numbers of chaetae were allowed to interbreed and eight flies with low numbers of chaetae were allowed to interbreed. Periodically they performed mate choice experiments on the two lines. They found that they had produced a high degree of positive assortative mating between the two groups. In the decade or so following this, eighteen labs attempted unsuccessfully to reproduce these results. References are given in Thoday and Gibson 1970.

• • Crossley (1974) was able to produce changes in mating behavior in two mutant strains of D. melanogaster. Four treatments were used. In each treatment, 55 virgin males and 55 virgin females of both ebony body mutant flies and vestigial wing mutant flies (220 flies total) were put into a jar and allowed to mate for 20 hours. The females were collected and each was put into a separate vial. The phenotypes of the offspring were recorded. Wild type offspring were hybrids between the mutants. In two of the four treatments, mating was carried out in the light. In one of these treatments all hybrid offspring were destroyed. This was repeated for 40 generations. Mating was carried out in the dark in the other two treatments. Again, in one of these all hybrids were destroyed. This was repeated for 49 generations. Crossley ran mate choice tests and observed mating behavior. Positive assortative mating was found in the treatment which had mated in the light and had been subject to strong selection against hybridization. The basis of this was changes in the courtship behaviors of both sexes. Similar experiments, without observation of mating behavior, were performed by Knight, et al. (1956).

• • Kilias, et al. (1980) exposed D. melanogaster populations to different temperature and humidity regimes for several years. They performed mating tests to check for reproductive isolation. They found some sterility in crosses among populations raised under different conditions. They also showed some positive assortative mating. These things were not observed in populations which were separated but raised under the same conditions. They concluded that sexual isolation was produced as a byproduct of selection.

• • In a series of papers (Rice 1985, Rice and Salt 1988 and Rice and Salt 1990) Rice and Salt presented experimental evidence for the possibility of sympatric speciation. They started from the premise that whenever organisms sort themselves into the environment first and then mate locally, individuals with the same habitat preferences will necessarily mate assortatively. They established a stock population of D. melanogaster with flies collected in an orchard near Davis, California. Pupae from the culture were placed into a habitat maze. Newly emerged flies had to negotiate the maze to find food. The maze simulated several environmental gradients simultaneously. The flies had to make three choices of which way to go. The first was between light and dark (phototaxis). The second was between up and down (geotaxis). The last was between the scent of acetaldehyde and the scent of ethanol (chemotaxis). This divided the flies among eight habitats. The flies were further divided by the time of day of emergence. In total the flies were divided among 24 spatio-temporal habitats.

• • • They next cultured two strains of flies that had chosen opposite habitats. One strain emerged early, flew upward and was attracted to dark and acetaldehyde. The other emerged late, flew downward and was attracted to light and ethanol. Pupae from these two strains were placed together in the maze. They were allowed to mate at the food site and were collected. Eye color differences between the strains allowed Rice and Salt to distinguish between the two strains. A selective penalty was imposed on flies that switched habitats. Females that switched habitats were destroyed. None of their gametes passed into the next generation. Males that switched habitats received no penalty. After 25 generations of this mating tests showed reproductive isolation between the two strains. Habitat specialization was also produced.

• • • They next repeated the experiment without the penalty against habitat switching. The result was the same -- reproductive isolation was produced. They argued that a switching penalty is not necessary to produce reproductive isolation. Their results, they stated, show the possibility of sympatric speciation.

• • In a series of experiments, del Solar (1966) derived positively and negatively geotactic and phototactic strains of D. pseudoobscura from the same population by running the flies through mazes. Flies from different strains were then introduced into mating chambers (10 males and 10 females from each strain). Matings were recorded. Statistically significant positive assortative mating was found.

• • • In a separate series of experiments Dodd (1989) raised eight populations derived from a single population of D. Pseudoobscura on stressful media. Four populations were raised on a starch based medium, the other four were raised on a maltose based medium. The fly populations in both treatments took several months to get established, implying that they were under strong selection. Dodd found some evidence of genetic divergence between flies in the two treatments. He performed mate choice tests among experimental populations. He found statistically significant assortative mating between populations raised on different media, but no assortative mating among populations raised within the same medium regime. He argued that since there was no direct selection for reproductive isolation, the behavioral isolation results from a pleiotropic by-product to adaptation to the two media. Schluter and Nagel (1995) have argued that these results provide experimental support for the hypothesis of parallel speciation.

• • • Less dramatic results were obtained by growing D. willistoni on media of different pH levels (de Oliveira and Cordeiro 1980). Mate choice tests after 26, 32, 52 and 69 generations of growth showed statistically significant assortative mating between some populations grown in different pH treatments. This ethological isolation did not always persist over time. They also found that some crosses made after 106 and 122 generations showed significant hybrid inferiority, but only when grown in acid medium.

• • Some proposed models of speciation rely on a process called reinforcement to complete the speciation process. Reinforcement occurs when to partially isolated allopatric populations come into contact. Lower relative fitness of hybrids between the two populations results in increased selection for isolating mechanisms. I should note that a recent review (Rice and Hostert 1993) argues that there is little experimental evidence to support reinforcement models. Two experiments in which the authors argue that their results provide support are discussed below.

• • • Ehrman (1971) established strains of wild-type and mutant (black body) D. melanogaster. These flies were derived from compound autosome strains such that heterotypic matings would produce no progeny. The two strains were reared together in common fly cages. After two years, the isolation index generated from mate choice experiments had increased from 0.04 to 0.43, indicating the appearance of considerable assortative mating. After four years this index had risen to 0.64 (Ehrman 1973).

• • • Along the same lines, Koopman (1950) was able to increase the degree of reproductive isolation between two partially isolated species, D. pseudoobscura and D. persimilis.

• The founder-flush (a.k.a. flush-crash) hypothesis posits that genetic drift and founder effects play a major role in speciation (Powell 1978). During a founder-flush cycle a new habitat is colonized by a small number of individuals (e.g. one inseminated female). The population rapidly expands (the flush phase). This is followed by the population crashing. During this crash period the population experiences strong genetic drift. The population undergoes another rapid expansion followed by another crash. This cycle repeats several times. Reproductive isolation is produced as a byproduct of genetic drift.

• • Dodd and Powell (1985) tested this hypothesis using D. pseudoobscura. A large, heterogeneous population was allowed to grow rapidly in a very large population cage. Twelve experimental populations were derived from this population from single pair matings. These populations were allowed to flush. Fourteen months later, mating tests were performed among the twelve populations. No postmating isolation was seen. One cross showed strong behavioral isolation. The populations underwent three more flush-crash cycles. Forty-four months after the start of the experiment (and fifteen months after the last flush) the populations were again tested. Once again, no postmating isolation was seen. Three populations showed behavioral isolation in the form of positive assortative mating. Later tests between 1980 and 1984 showed that the isolation persisted, though it was weaker in some cases.

• • Galina, et al. (1993) performed similar experiments with D. pseudoobscura. Mating tests between populations that underwent flush-crash cycles and their ancestral populations showed 8 cases of positive assortative mating out of 118 crosses. They also showed 5 cases of negative assortative mating (i.e. the flies preferred to mate with flies of the other strain). Tests among the founder-flush populations showed 36 cases of positive assortative mating out of 370 crosses. These tests also found 4 cases of negative assortative mating. Most of these mating preferences did not persist over time. Galina, et al. concluded that the founder-flush protocol yields reproductive isolation only as a rare and erratic event.

• • Ahearn (1980) applied the founder-flush protocol to D. silvestris. Flies from a line of this species underwent several flush-crash cycles. They were tested in mate choice experiments against flies from a continuously large population. Female flies from both strains preferred to mate with males from the large population. Females from the large population would not mate with males from the founder flush population. An asymmetric reproductive isolation was produced.

• • In a three year experiment, Ringo, et al. (1985) compared the effects of a founder-flush protocol to the effects of selection on various traits. A large population of D. simulans was created from flies from 69 wild caught stocks from several locations. Founder-flush lines and selection lines were derived from this population. The founder-flush lines went through six flush-crash cycles. The selection lines experienced equal intensities of selection for various traits. Mating test were performed between strains within a treatment and between treatment strains and the source population. Crosses were also checked for postmating isolation. In the selection lines, 10 out of 216 crosses showed positive assortative mating (2 crosses showed negative assortative mating). They also found that 25 out of 216 crosses showed postmating isolation. Of these, 9 cases involved crosses with the source population. In the founder-flush lines 12 out of 216 crosses showed positive assortative mating (3 crosses showed negative assortative mating). Postmating isolation was found in 15 out of 216 crosses, 11 involving the source population. They concluded that only weak isolation was found and that there was little difference between the effects of natural selection and the effects of genetic drift.

• A final test of the founder-flush hypothesis will be described with the housefly cases below.

• • Meffert and Bryant (1991) used houseflies to test whether bottlenecks in populations can cause permanent alterations in courtship behavior that lead to premating isolation. They collected over 100 flies of each sex from a landfill near Alvin, Texas. These were used to initiate an ancestral population. From this ancestral population they established six lines. Two of these lines were started with one pair of flies, two lines were started with four pairs of flies and two lines were started with sixteen pairs of flies. These populations were flushed to about 2,000 flies each. They then went through five bottlenecks followed by flushes. This took 35 generations. Mate choice tests were performed. One case of positive assortative mating was found. One case of negative assortative mating was also found.

• • Soans, et al. (1974) used houseflies to test Pimentel's model of speciation. This model posits that speciation requires two steps. The first is the formation of races in subpopulations. This is followed by the establishment of reproductive isolation. Houseflies were subjected to intense divergent selection on the basis of positive and negative geotaxis. In some treatments no gene flow was allowed, while in others there was 30% gene flow. Selection was imposed by placing 1000 flies into the center of a 108 cm vertical tube. The first 50 flies that reached the top and the first 50 flies that reached the bottom were used to found positively and negatively geotactic populations. Four populations were established:

Population A + geotaxis, no gene flow Population B - geotaxis, no gene flow Population C + geotaxis, 30% gene flow Population D - geotaxis, 30% gene flow

Selection was repeated within these populations each generations. After 38 generations the time to collect 50 flies had dropped from 6 hours to 2 hours in Pop A, from 4 hours to 4 minutes in Pop B, from 6 hours to 2 hours in Pop C and from 4 hours to 45 minutes in Pop D. Mate choice tests were performed. Positive assortative mating was found in all crosses. They concluded that reproductive isolation occurred under both allopatric and sympatric conditions when very strong selection was present.

Hurd and Eisenberg (1975) performed a similar experiment on houseflies using 50% gene flow and got the same results.

• Recently there has been a lot of interest in whether the differentiation of an herbivorous or parasitic species into races living on different hosts can lead to sympatric speciation. It has been argued that in animals that mate on (or in) their preferred hosts, positive assortative mating is an inevitable byproduct of habitat selection (Rice 1985; Barton, et al. 1988). This would suggest that differentiated host races may represent incipient species.

• Rhagoletis pomonella is a fly that is native to North America. Its normal host is the hawthorn tree. Sometime during the nineteenth century it began to infest apple trees. Since then it has begun to infest cherries, roses, pears and possibly other members of the rosaceae. Quite a bit of work has been done on the differences between flies infesting hawthorn and flies infesting apple. There appear to be differences in host preferences among populations. Offspring of females collected from on of these two hosts are more likely to select that host for oviposition (Prokopy et al. 1988). Genetic differences between flies on these two hosts have been found at 6 out of 13 allozyme loci (Feder et al. 1988, see also McPheron et al. 1988). Laboratory studies have shown an asynchrony in emergence time of adults between these two host races (Smith 1988). Flies from apple trees take about 40 days to mature, whereas flies from hawthorn trees take 54-60 days to mature. This makes sense when we consider that hawthorn fruit tends to mature later in the season that apples. Hybridization studies show that host preferences are inherited, but give no evidence of barriers to mating. This is a very exciting case. It may represent the early stages of a sympatric speciation event (considering the dispersal of R. pomonella to other plants it may even represent the beginning of an adaptive radiation). It is important to note that some of the leading researchers on this question are urging caution in interpreting it. Feder and Bush (1989) stated:

"Hawthorn and apple "host races" of R. pomonella may therefore represent incipient species. However, it remains to be seen whether host-associated traits can evolve into effective enough barriers to gene flow to result eventually in the complete reproductive isolation of R. pomonella populations."

• Eurosta solidaginis is a gall forming fly that is associated with goldenrod plants. It has two hosts: over most of its range it lays its eggs in Solidago altissima, but in some areas it uses S. gigantea as its host. Recent electrophoretic work has shown that the genetic distances among flies from different sympatric hosts species are greater than the distances among flies on the same host in different geographic areas (Waring et al. 1990). This same study also found reduced variability in flies on S. gigantea. This suggests that some E. solidaginis have recently shifted hosts to this species. A recent study has compared reproductive behavior of the flies associated with the two hosts (Craig et al. 1993). They found that flies associated with S. gigantea emerge earlier in the season than flies associated with S. altissima. In host choice experiments, each fly strain ovipunctured its own host much more frequently than the other host. Craig et al. (1993) also performed several mating experiments. When no host was present and females mated with males from either strain, if males from only one strain were present. When males of both strains were present, statistically significant positive assortative mating was seen. In the presence of a host, assortative mating was also seen. When both hosts and flies from both populations were present, females waited on the buds of the host that they are normally associated with. The males fly to the host to mate. Like the Rhagoletis case above, this may represent the beginning of a sympatric speciation.

• Halliburton and Gall (1981) established a population of flour beetles collected in Davis, California. In each generation they selected the 8 lightest and the 8 heaviest pupae of each sex. When these 32 beetles had emerged, they were placed together and allowed to mate for 24 hours. Eggs were collected for 48 hours. The pupae that developed from these eggs were weighed at 19 days. This was repeated for 15 generations. The results of mate choice tests between heavy and light beetles was compared to tests among control lines derived from randomly chosen pupae. Positive assortative mating on the basis of size was found in 2 out of 4 experimental lines.

In 1964 five or six individuals of the polychaete worm, Nereis acuminata, were collected in Long Beach Harbor, California. These were allowed to grow into a population of thousands of individuals. Four pairs from this population were transferred to the Woods Hole Oceanographic Institute. For over 20 years these worms were used as test organisms in environmental toxicology. From 1986 to 1991 the Long Beach area was searched for populations of the worm. Two populations, P1 and P2, were found. Weinberg, et al. (1992) performed tests on these two populations and the Woods Hole population (WH) for both postmating and premating isolation. To test for postmating isolation, they looked at whether broods from crosses were successfully reared. The results below give the percentage of successful rearings for each group of crosses.

WH × WH - 75% P1 × P1 - 95% P2 × P2 - 80% P1 × P2 - 77% WH × P1 - 0% WH × P2 - 0%

They also found statistically significant premating isolation between the WH population and the field populations. Finally, the Woods Hole population showed slightly different karyotypes from the field populations.

In some species the presence of intracellular bacterial parasites (or symbionts) is associated with postmating isolation. This results from a cytoplasmic incompatability between gametes from strains that have the parasite (or symbiont) and stains that don't. An example of this is seen in the mosquito Culex pipiens (Yen and Barr 1971). Compared to within strain matings, matings between strains from different geographic regions may may have any of three results: These matings may produce a normal number of offspring, they may produce a reduced number of offspring or they may produce no offspring. Reciprocal crosses may give the same or different results. In an incompatible cross, the egg and sperm nuclei fail to unite during fertilization. The egg dies during embryogenesis. In some of these strains, Yen and Barr (1971) found substantial numbers of Rickettsia-like microbes in adults, eggs and embryos. Compatibility of mosquito strains seems to be correlated with the strain of the microbe present. Mosquitoes that carry different strains of the microbe exhibit cytoplasmic incompatibility; those that carry the same strain of microbe are interfertile.

Similar phenomena have been seen in a number of other insects. Microoganisms are seen in the eggs of both Nasonia vitripennis and N. giraulti. These two species do not normally hybridize. Following treatment with antibiotics, hybrids occur between them (Breeuwer and Werren 1990). In this case, the symbiont is associated with improper condensation of host chromosomes.

For more examples and a critical review of this topic, see Thompson 1987.

So far the BSC has applied to all of the experiments discussed. The following are a couple of major morphological changes produced in asexual species. Do these represent speciation events? The answer depends on how species is defined.

• Boraas (1983) reported the induction of multicellularity in a strain of Chlorella pyrenoidosa (since reclassified as C. vulgaris) by predation. He was growing the unicellular green alga in the first stage of a two stage continuous culture system as for food for a flagellate predator, Ochromonas sp., that was growing in the second stage. Due to the failure of a pump, flagellates washed back into the first stage. Within five days a colonial form of the Chlorella appeared. It rapidly came to dominate the culture. The colony size ranged from 4 cells to 32 cells. Eventually it stabilized at 8 cells. This colonial form has persisted in culture for about a decade. The new form has been keyed out using a number of algal taxonomic keys. They key out now as being in the genus Coelosphaerium, which is in a different family from Chlorella.

• Shikano, et al. (1990) reported that an unidentified bacterium underwent a major morphological change when grown in the presence of a ciliate predator. This bacterium's normal morphology is a short (1.5 um) rod. After 8 - 10 weeks of growing with the predator it assumed the form of long (20 um) cells. These cells have no cross walls. Filaments of this type have also been produced under circumstances similar to Boraas' induction of multicellularity in Chlorella. Microscopic examination of these filaments is described in Gillott et al. (1993). Multicellularity has also been produced in unicellular bacterial by predation (Nakajima and Kurihara 1994). In this study, growth in the presence of protozoal grazers resulted in the production of chains of bacterial cells.

[edit] Creationism

Mammals were created in a finite number of distinct and original forms, with characteristics particular to their form. A great number of these mammals died in the flood and their fossilized remains can be observed. The mammals that were taken onto the ark during the flood were released, dispersed, and through reproductive isolation, variation, and natural selection, evolved into the current diversity of mammals.

• It is argued that the creationist theory is superior, because:
  • It can explain how mammals all came to share so many irreducibly complex characteristics which are so radically different from other taxa, whereas the evolutionary theory either requires that all the uniquely mammalian characteristics developed by chance in the original population of protomammals before any differentiation took place, or that the uniquely mammalian characteristics developed independently in each of the lower taxa of mammals after they differentiated, neither of which is explicable or supported by any evidence.
  • It can explain why there is no evidence of "missing links" between reptiles and mammals, which shared more than superficial similarities with one or the other (examples of reptiles with such superficial similarities to mammals include the cynodont, inferred from two molars found in Arizona, which mainstream scientists propose is the missing link between mammals and reptiles, because the teeth are of similar form to those of canines).

[edit] Mainstream science

Mammals share a common ancestor with reptiles.

• Reptiles and mammals both have amniotic eggs. The page on the phylum chordata provides a more detailed account of the classification of reptiles and mammals.

Transition from synapsid reptiles to mammals is the best-documented transition between vertebrate classes. So far this series is known only as a series of genera or families; the transitions from species to species are not known. But the family sequence is quite complete. Each group is clearly related to both the group that came before, and the group that came after, and yet the sequence is so long that the fossils at the end are astoundingly different from those at the beginning. As Rowe recently said about this transition (in Szalay et al., 1993), "When sampling artifact is removed and all available character data analyzed [with computer phylogeny programs that do not assume anything about evolution], a highly corroborated, stable phylogeny remains, which is largely consistent with the temporal distributions of taxa recorded in the fossil record." Similarly, Gingerich has stated (1977) "While living mammals are well separated from other groups of animals today, the fossil record clearly shows their origin from a reptilian stock and permits one to trace the origin and radiation of mammals in considerable detail." For more details, see Kermack's superb and readable little book (1984), Kemp's more detailed but older book (1982), and read Szalay et al.'s recent collection of review articles (1993, vol. 1).

This list starts with pelycosaurs (early synapsid reptiles) and continues with therapsids and cynodonts up to the first unarguable "mammal". Most of the changes in this transition involved elaborate repackaging of an expanded brain and special sense organs, remodeling of the jaws & teeth for more efficient eating, and changes in the limbs & vertebrae related to active, legs-under-the-body locomotion. Here are some differences to keep an eye on:

Early Reptiles vs .Mammals

1. No fenestrae in skull vs. massive fenestra exposes all of braincase
2. Braincase attached loosely vs. braincase attached firmly to skull
3. No secondary palate vs. complete bony secondary palate
4. Undifferentiated dentition vs. incisors, canines, premolars, molars
5. Cheek teeth uncrowned points vs. cheek teeth (PM & M) crowned & cusped
6. Teeth replaced continuously vs. teeth replaced once at most
7. Teeth with single root vs. molars double-rooted
8. Jaw joint quadrate-articular vs. jaw joint dentary-squamosal (*)
9. Lower jaw of several bones vs lower jaw of dentary bone only
10. Single ear bone (stapes) vs. three ear bones (stapes, incus, malleus)
11. Joined external nares vs. separate external nares
12. Single occipital condyle vs. double occipital condyle
13. Long cervical ribs vs. cervical ribs tiny, fused to vertebrae
14. Lumbar region with ribs vs. lumbar region rib-free
15. No diaphragm vs. diaphragm
16. Limbs sprawled out from body vs. limbs under body
17. Scapula simple vs. scapula with big spine for muscles
18. Pelvic bones unfused Pelvis fused
19. Two sacral (hip) vertebrae vs. three or more sacral vertebrae
20. Toe bone #'s 2-3-4-5-4 vs. toe bones 2-3-3-3-3
21. Body temperature variable vs. body temperature constant

(*) The presence of a dentary-squamosal jaw joint has been arbitrarily selected as the defining trait of a mammal.

• Paleothyris (early Pennsylvanian) -- An early captorhinomorph reptile, with no temporal fenestrae at all.
• Protoclepsydrops haplous (early Pennsylvanian) -- The earliest known synapsid reptile. Little temporal fenestra, with all surrounding bones intact. Fragmentary. Had amphibian-type vertebrae with tiny neural processes. (reptiles had only just separated from the amphibians)
• Clepsydrops (early Pennsylvanian) -- The second earliest known synapsid. These early, very primitive synapsids are a primitive group of pelycosaurs collectively called "ophiacodonts".
• Archaeothyris (early-mid Pennsylvanian) -- A slightly later ophiacodont. Small temporal fenestra, now with some reduced bones (supratemporal). Braincase still just loosely attached to skull. Slight hint of different tooth types. Still has some extremely primitive, amphibian/captorhinid features in the jaw, foot, and skull. Limbs, posture, etc. typically reptilian, though the ilium (major hip bone) was slightly enlarged.
• Varanops (early Permian) -- Temporal fenestra further enlarged. Braincase floor shows first mammalian tendencies & first signs of stronger attachment to rest of skull (occiput more strongly attached). Lower jaw shows first changes in jaw musculature (slight coronoid eminence). Body narrower, deeper: vertebral column more strongly constructed. Ilium further enlarged, lower-limb musculature starts to change (prominent fourth trochanter on femur). This animal was more mobile and active. Too late to be a true ancestor, and must be a "cousin".
• Haptodus (late Pennsylvanian) -- One of the first known sphenacodonts, showing the initiation of sphenacodont features while retaining many primitive features of the ophiacodonts. Occiput still more strongly attached to the braincase. Teeth become size-differentiated, with biggest teeth in canine region and fewer teeth overall. Stronger jaw muscles. Vertebrae parts & joints more mammalian. Neural spines on vertebrae longer. Hip strengthened by fusing to three sacral vertebrae instead of just two. Limbs very well developed.
• Dimetrodon, Sphenacodon or a similar sphenacodont (late Pennsylvanian to early Permian, 270 Ma) -- More advanced pelycosaurs, clearly closely related to the first therapsids (next). Dimetrodon is almost definitely a "cousin" and not a direct ancestor, but as it is known from very complete fossils, it's a good model for sphenacodont anatomy. Medium-sized fenestra. Teeth further differentiated, with small incisors, two huge deep- rooted upper canines on each side, followed by smaller cheek teeth, all replaced continuously. Fully reptilian jaw hinge. Lower jaw bone made of multiple bones & with first signs of a bony prong later involved in the eardrum, but there was no eardrum yet, so these reptiles could only hear ground-borne vibrations (they did have a reptilian middle ear). Vertebrae had still longer neural spines (spectacularly so in Dimetrodon, which had a sail), and longer transverse spines for stronger locomotion muscles.
• Biarmosuchia (late Permian) -- A therocephalian -- one of the earliest, most primitive therapsids. Several primitive, sphenacodontid features retained: jaw muscles inside the skull, platelike occiput, palatal teeth. New features: Temporal fenestra further enlarged, occupying virtually all of the cheek, with the supratemporal bone completely gone. Occipital plate slanted slightly backwards rather than forwards as in pelycosaurs, and attached still more strongly to the braincase. Upper jaw bone (maxillary) expanded to separate lacrymal from nasal bones, intermediate between early reptiles and later mammals. Still no secondary palate, but the vomer bones of the palate developed a backward extension below the palatine bones. This is the first step toward a secondary palate, and with exactly the same pattern seen in cynodonts. Canine teeth larger, dominating the dentition. Variable tooth replacement: some therocephalians (e.g Scylacosaurus) had just one canine, like mammals, and stopped replacing the canine after reaching adult size. Jaw hinge more mammalian in position and shape, jaw musculature stronger (especially the mammalian jaw muscle). The amphibian-like hinged upper jaw finally became immovable. Vertebrae still sphenacodontid-like. Radical alteration in the method of locomotion, with a much more mobile forelimb, more upright hindlimb, & more mammalian femur & pelvis. Primitive sphenacodontid humerus. The toes were approaching equal length, as in mammals, with #toe bones varying from reptilian to mammalian. The neck & tail vertebrae became distinctly different from trunk vertebrae. Probably had an eardrum in the lower jaw, by the jaw hinge.
• Procynosuchus (latest Permian) -- The first known cynodont -- a famous group of very mammal-like therapsid reptiles, sometimes considered to be the first mammals. Probably arose from the therocephalians, judging from the distinctive secondary palate and numerous other skull characters. Enormous temporal fossae for very strong jaw muscles, formed by just one of the reptilian jaw muscles, which has now become the mammalian masseter. The large fossae is now bounded only by the thin zygomatic arch (cheekbone to you & me). Secondary palate now composed mainly of palatine bones (mammalian), rather than vomers and maxilla as in older forms; it's still only a partial bony palate (completed in life with soft tissue). Lower incisor teeth was reduced to four (per side), instead of the previous six (early mammals had three). Dentary now is 3/4 of lower jaw; the other bones are now a small complex near the jaw hinge. Jaw hinge still reptilian. Vertebral column starts to look mammalian: first two vertebrae modified for head movements, and lumbar vertebrae start to lose ribs, the first sign of functional division into thoracic and lumbar regions. Scapula beginning to change shape. Further enlargement of the ilium and reduction of the pubis in the hip. A diaphragm may have been present.
• Dvinia [also "Permocynodon"] (latest Permian) -- Another early cynodont. First signs of teeth that are more than simple stabbing points -- cheek teeth develop a tiny cusp. The temporal fenestra increased still further. Various changes in the floor of the braincase; enlarged brain. The dentary bone was now the major bone of the lower jaw. The other jaw bones that had been present in early reptiles were reduced to a complex of smaller bones near the jaw hinge. Single occipital condyle splitting into two surfaces. The postcranial skeleton of Dvinia is virtually unknown and it is not therefore certain whether the typical features found at the next level had already evolved by this one. *Metabolic rate was probably increased, at least approaching homeothermy.
• Thrinaxodon (early Triassic) -- A more advanced "galesaurid" cynodont. Further development of several of the cynodont features seen already. Temporal fenestra still larger, larger jaw muscle attachments. Bony secondary palate almost complete. Functional division of teeth: incisors (four uppers and three lowers), canines, and then 7-9 cheek teeth with cusps for chewing. The cheek teeth were all alike, though (no premolars & molars), did not occlude together, were all single- rooted, and were replaced throughout life in alternate waves. Dentary still larger, with the little quadrate and articular bones were loosely attached. The stapes now touched the inner side of the quadrate. First sign of the mammalian jaw hinge, a ligamentous connection between the lower jaw and the squamosal bone of the skull. The occipital condyle is now two slightly separated surfaces, though not separated as far as the mammalian double condyles. Vertebral connections more mammalian, and lumbar ribs reduced. Scapula shows development of a new mammalian shoulder muscle. Ilium increased again, and all four legs fully upright, not sprawling. Tail short, as is necessary for agile quadrupedal locomotion. The whole locomotion was more agile. Number of toe bones is 2.3.4.4.3, intermediate between reptile number (2.3.4.5.4) and mammalian (2.3.3.3.3), and the "extra" toe bones were tiny. Nearly complete skeletons of these animals have been found curled up - a possible reaction to conserve heat, indicating possible endothermy? Adults and juveniles have been found together, possibly a sign of parental care. The specialization of the lumbar area (e.g. reduction of ribs) is indicative of the presence of a diaphragm, needed for higher O2 intake and homeothermy. NOTE on hearing: The eardrum had developed in the only place available for it -- the lower jaw, right near the jaw hinge, supported by a wide prong (reflected lamina) of the angular bone. These animals could now hear airborne sound, transmitted through the eardrum to two small lower jaw bones, the articular and the quadrate, which contacted the stapes in the skull, which contacted the cochlea. Rather a roundabout system and sensitive to low-frequency sound only, but better than no eardrum at all! Cynodonts developed quite loose quadrates and articulars that could vibrate freely for sound transmittal while still functioning as a jaw joint, strengthened by the mammalian jaw joint right next to it. All early mammals from the Lower Jurassic have this low-frequency ear and a double jaw joint. By the middle Jurassic, mammals lost the reptilian joint (though it still occurs briefly in embryos) and the two bones moved into the nearby middle ear, became smaller, and became much more sensitive to high-frequency sounds.
• Cynognathus (early Triassic, 240 Ma; suspected to have existed even earlier) -- We're now at advanced cynodont level. Temporal fenestra larger. Teeth differentiating further; cheek teeth with cusps met in true occlusion for slicing up food, rate of replacement reduced, with mammalian-style tooth roots (though single roots). Dentary still larger, forming 90% of the muscle-bearing part of the lower jaw. TWO JAW JOINTS in place, mammalian and reptilian: A new bony jaw joint existed between the squamosal (skull) and the surangular bone (lower jaw), while the other jaw joint bones were reduced to a compound rod lying in a trough in the dentary, close to the middle ear. Ribs more mammalian. Scapula halfway to the mammalian condition. Limbs were held under body. There is possible evidence for fur in fossil pawprints.
• Diademodon (early Triassic, 240 Ma; same strata as Cynognathus) -- Temporal fenestra larger still, for still stronger jaw muscles. True bony secondary palate formed exactly as in mammals, but didn't extend quite as far back. Turbinate bones possibly present in the nose (warm-blooded?). Dental changes continue: rate of tooth replacement had decreased, cheek teeth have better cusps & consistent wear facets (better occlusion). Lower jaw almost entirely dentary, with tiny articular at the hinge. Still a double jaw joint. Ribs shorten suddenly in lumbar region, probably improving diaphragm function & locomotion. Mammalian toe bones (2.3.3.3.3), with closely related species still showing variable numbers.
• Probelesodon (mid-Triassic; South America) -- Fenestra very large, still separate from eyesocket (with postorbital bar). Secondary palate longer, but still not complete. Teeth double-rooted, as in mammals. Nares separated. Second jaw joint stronger. Lumbar ribs totally lost; thoracic ribs more mammalian, vertebral connections very mammalian. Hip & femur more mammalian.
• Probainognathus (mid-Triassic, 239-235 Ma, Argentina) -- Larger brain with various skull changes: pineal foramen ("third eye") closes, fusion of some skull plates. Cheekbone slender, low down on the side of the eye socket. Postorbital bar still there. Additional cusps on cheek teeth. Still two jaw joints. Still had cervical ribs & lumbar ribs, but they were very short. Reptilian "costal plates" on thoracic ribs mostly lost. Mammalian #toe bones.
• Exaeretodon (mid-late Triassic, 239Ma, South America) -- (Formerly lumped with the herbivorous gomphodont cynodonts.) Mammalian jaw prong forms, related to eardrum support. Three incisors only (mammalian). Costal plates completely lost. More mammalian hip related to having limbs under the body. Possibly the first steps toward coupling of locomotion & breathing. This is probably a "cousin" fossil not directly ancestral, as it has several new but non-mammalian teeth traits.
• GAP of about 30 my in the late Triassic, from about 239-208 Ma. Only one early mammal fossil is known from this time. The next time fossils are found in any abundance, tritylodontids and trithelodontids had already appeared, leading to some very heated controversy about their relative placement in the chain to mammals. Recent discoveries seem to show trithelodontids to be more mammal- like, with tritylodontids possibly being an offshoot group (see Hopson 1991, Rowe 1988, Wible 1991, and Shubin et al. 1991). Bear in mind that both these groups were almost fully mammalian in every feature, lacking only the final changes in the jaw joint and middle ear.
• Oligokyphus, Kayentatherium (early Jurassic, 208 Ma) -- These are tritylodontids, an advanced cynodont group. Face more mammalian, with changes around eyesocket and cheekbone. Full bony secondary palate. Alternate tooth replacement with double-rooted cheek teeth, but without mammalian-style tooth occlusion (which some earlier cynodonts already had). Skeleton strikingly like egg- laying mammals (monotremes). Double jaw joint. More flexible neck, with mammalian atlas & axis and double occipital condyle. Tail vertebrae simpler, like mammals. Scapula is now substantially mammalian, and the forelimb is carried directly under the body. Various changes in the pelvis bones and hind limb muscles; this animal's limb musculature and locomotion were virtually fully mammalian. Probably cousin fossils (?), with Oligokyphus being more primitive than Kayentatherium. Thought to have diverged from the trithelodontids during that gap in the late Triassic. There is disagreement about whether the tritylodontids were ancestral to mammals (presumably during the late Triassic gap) or whether they are a specialized offshoot group not directly ancestral to mammals.
• Pachygenelus, Diarthrognathus (earliest Jurassic, 209 Ma) -- These are trithelodontids, a slightly different advanced cynodont group. New discoveries (Shubin et al., 1991) show that these animals are very close to the ancestry of mammals. Inflation of nasal cavity, establishment of Eustachian tubes between ear and pharynx, loss of postorbital bar. Alternate replacement of mostly single- rooted teeth. This group also began to develop double tooth roots -- in Pachygenelus the single root of the cheek teeth begins to split in two at the base. Pachygenelus also has mammalian tooth enamel, and mammalian tooth occlusion. Double jaw joint, with the second joint now a dentary-squamosal (instead of surangular), fully mammalian. Incipient dentary condyle. Reptilian jaw joint still present but functioning almost entirely in hearing; postdentary bones further reduced to tiny rod of bones in jaw near middle ear; probably could hear high frequencies now. More mammalian neck vertebrae for a flexible neck. Hip more mammalian, with a very mammalian iliac blade & femur. Highly mobile, mammalian-style shoulder. Probably had coupled locomotion & breathing. These are probably "cousin" fossils, not directly ancestral (the true ancestor is thought to have occurred during that late Triassic gap). Pachygenelus is pretty close, though.
• Adelobasileus cromptoni (late Triassic; 225 Ma, west Texas) -- A recently discovered fossil proto-mammal from right in the middle of that late Triassic gap! Currently the oldest known "mammal." Only the skull was found. "Some cranial features of Adelobasileus, such as the incipient promontorium housing the cochlea, represent an intermediate stage of the character transformation from non-mammalian cynodonts to Liassic mammals" (Lucas & Luo, 1993). This fossil was found from a band of strata in the western U.S. that had not previously been studied for early mammals. Also note that this fossil dates from slightly before the known tritylodonts and trithelodonts, though it has long been suspected that tritilodonts and trithelodonts were already around by then. Adelobasileus is thought to have split off from either a trityl. or a trithel., and is either identical to or closely related to the common ancestor of all mammals.
• Sinoconodon (early Jurassic, 208 Ma) -- The next known very ancient proto-mammal. Eyesocket fully mammalian now (closed medial wall). Hindbrain expanded. Permanent cheekteeth, like mammals, but the other teeth were still replaced several times. Mammalian jaw joint stronger, with large dentary condyle fitting into a distinct fossa on the squamosal. This final refinement of the joint automatically makes this animal a true "mammal". Reptilian jaw joint still present, though tiny.
• Kuehneotherium (early Jurassic, about 205 Ma) -- A slightly later proto-mammal, sometimes considered the first known pantothere (primitive placental-type mammal). Teeth and skull like a placental mammal. The three major cusps on the upper & lower molars were rotated to form interlocking shearing triangles as in the more advanced placental mammals & marsupials. Still has a double jaw joint, though.
• Eozostrodon, Morganucodon, Haldanodon (early Jurassic, ~205 Ma) -- A group of early proto-mammals called "morganucodonts". The restructuring of the secondary palate and the floor of the braincase had continued, and was now very mammalian. Truly mammalian teeth: the cheek teeth were finally differentiated into simple premolars and more complex molars, and teeth were replaced only once. Triangular- cusped molars. Reversal of the previous trend toward reduced incisors, with lower incisors increasing to four. Tiny remnant of the reptilian jaw joint. Once thought to be ancestral to monotremes only, but now thought to be ancestral to all three groups of modern mammals -- monotremes, marsupials, and placentals.
• Peramus (late Jurassic, about 155 Ma) -- A "eupantothere" (more advanced placental-type mammal). The closest known relative of the placentals & marsupials. Triconodont molar has with more defined cusps. This fossil is known only from teeth, but judging from closely related eupantotheres (e.g. Amphitherium) it had finally lost the reptilian jaw joint, attaing a fully mammalian three-boned middle ear with excellent high-frequency hearing. Has only 8 cheek teeth, less than other eupantotheres and close to the 7 of the first placental mammals. Also has a large talonid on its "tribosphenic" molars, almost as large as that of the first placentals -- the first development of grinding capability.
• Endotherium (very latest Jurassic, 147 Ma) -- An advanced eupantothere. Fully tribosphenic molars with a well- developed talonid. Known only from one specimen. From Asia; recent fossil finds in Asia suggest that the tribosphenic molar evolved there.
• Kielantherium and Aegialodon (early Cretaceous) -- More advanced eupantotheres known only from teeth. Kielantherium is from Asia and is known from slightly older strata than the European Aegialodon. Both have the talonid on the lower molars. The wear on it indicates that a major new cusp, the protocone, had evolved on the upper molars. By the Middle Cretaceous, animals with the new tribosphenic molar had spread into North America too (North America was still connected to Europe.)
• Steropodon galmani (early Cretaceous) -- The first known definite monotreme, discovered in 1985.
• Vincelestes neuquenianus (early Cretaceous, 135 Ma) -- A probably-placental mammal with some marsupial traits, known from some nice skulls. Placental-type braincase and coiled cochlea. Its intracranial arteries & veins ran in a composite monotreme/placental pattern derived from homologous extracranial vessels in the cynodonts. (Rougier et al., 1992)
• Pariadens kirklandi (late Cretaceous, about 95 Ma) -- The first definite marsupial. Known only from teeth.
• Kennalestes and Asioryctes (late Cretaceous, Mongolia) -- Small, slender animals; eyesocket open behind; simple ring to support eardrum; primitive placental-type brain with large olfactory bulbs; basic primitive tribosphenic tooth pattern. Canine now double rooted. Still just a trace of a non-dentary bone, the coronoid, on the otherwise all-dentary jaw. "Could have given rise to nearly all subsequent placentals." says Carroll (1988).
• Cimolestes, Procerberus, Gypsonictops (very late Cretaceous) -- Primitive North American placentals with same basic tooth pattern.

So, by the late Cretaceous the three groups of modern mammals were in place: monotremes, marsupials, and placentals. Placentals appear to have arisen in East Asia and spread to the Americas by the end of the Cretaceous. In the latest Cretaceous, placentals and marsupials had started to diversify a bit, and after the dinosaurs died out, in the Paleocene, this diversification accelerated. For instance, in the mid- Paleocene the placental fossils include a very primitive primate-like animal (Purgatorius - known only from a tooth, though, and may actually be an early ungulate), a herbivore-like jaw with molars that have flatter tops for better grinding (Protungulatum, probably an early ungulate), and an insectivore (Paranyctoides).

The decision as to which was the first mammal is somewhat subjective. We are placing an inflexible classification system on a gradational series. What happened was that an intermediate group evolved from the 'true' reptiles, which gradually acquired mammalian characters until a point was reached where we have artificially drawn a line between reptiles and mammals. For instance, Pachygenulus and Kayentatherium are both far more mammal-like than reptile-like, but they are both called "reptiles".

[edit] Creationism

• Creationists claim that mainstream scientists systematically fail to address their ideas and critiques on the merits, but merely prove by assertion and authority, particularly the phrase, "the majority of mainstream scientists believe ..." (Bandwagon fallacy).
• Creationists claim that evolutionists often argue against creationism in the manner of "your theory doesn't work under my theory, so your theory is wrong". An example is arguing that rapid plate tectonics would result in ocean floors of essentially the same age, and seeking to refute that by quoting "ages" derived from uniformitarian principles.
• Creationists believe that this enclave of scientific "consensus" supporting evolution is maintained in large part by systematically excluding creationism from scientific discourse.
• Creationists claim that they are excluded from scientific discourse in the following ways:
  • There is discrimination against those with creationist beliefs, including name-calling, denial of tenure and promotion even while qualified. This is likely related to 92% of the scientific community doubting or disbelieving God.
  • Scientific philosophy has been redefined in such a way as to exclude theistic causes for phenomenon, leaving no alternative but evolution, despite the possibility of theistic causes which creationists believe to be more reasonable.
  • Academic coursework is so steeped in evolutionary ideology as to make a creationist trying to get through evolutionary biology coursework feel much the same as an atheist trying to get through seminary.
  • Creationary organizations require belief in creation for membership, because they are excluded from secular scientific discourse, and therefore must conserve their efforts.
  • Evolutionists often quote them out of context and represent them as believing things that they don't (straw man fallacy), or not believing things that they do, such as plate tectonics.
  • Evolutionists often engage in dubious tactics in debate.
  • Scientific Journals generally will not publish papers that support creation. This is an example of academic bias.

[edit] Mainstream science

• Mainstream scientists assert that the various creationist theories proposed are unscientific because either:
  • The theory does not make testable predictions.
  • The theory is not falsifiable
  • The theory is far more complex than existing theories (without explaining more data) and so falls foul of Occam's razor.
  • The predictions that the theory is said to make cannot be agreed upon.
• Many "creationist" organisations purporting to be scientific have a criterion of membership which involves a statement of belief in a creator. This is an example of academic bias.
• This amicus brief was filed on August 18, 1986 for the Edwards v. Aguillard supreme court case (in the USA). The amicus was signed by 72 Nobel laureates, 17 state academies of science, and 7 other scientific organizations. This amicus brief argues that "creation-science" is actually religious dogma.
• Stephen J Gould repeatedly complained that he was misquoted by creationists. Many examples of alleged creationist misquotes can be viewed at [7].
• Mainstream scientists assert that many attempts have in the past been made by creationists to pass leglislation for the following aims:
  • Establish teaching of creationism in US schools.
  • Ban the teaching of evolution in US schools.
• Some of these attempts have been successful in the past. (see the Scopes trial)
• Creationists often link evolution with perceived moral failings in society. For an example see this article published online by creationists.
• Mainstream scientists assert that creationists often engage in dubious tactics in debate. They give many examples, some of which are:
  • Trying to shift the burden of proof away from the creationist side.
  • Argument from ignorance.
  • Redefining the rules of science, thus allowing themselves to use argument from ignorance.
  • Groundless accusations - for example calling evidence "fake" when they don't want to accept it.
• Explaining something by reference to a deity is not scientific. This is not to say that such explanations are not valid. They may be appropriate in some circumstances; but such an explanation would not count as science but as theology.
• Creationism contains a number of contradictions which cannot be explained.
  • If God created all creatures and loved them, why did many millions become extinct? How do creationists explain the creation and subsequent extinction of the dinosaurs? Early man? Hominids? Australopithicus?
  • Lewis Leakey has found evidence that several species of hominids were contemporaries, yet the Bible only describes the creation of one human. These theories are mutually exclusive. To accept the creation of a sole human is to deny the existence of fossilized evidence of tens of hominids.