Misunderstandings about evolution

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Although the modern synthesis of biological evolution is a major achievement of modern science and has spawned the development of the field of evolutionary biology, some aspects of it are often misunderstood. These misunderstandings about evolution have hindered the public's acceptance of the modern synthesis,^[1][2] most notably in the United States.^[3] Some of the most common misunderstandings are outlined in this article.

Contents 1 Evolution as theory and fact 2 Evolution, complexity, and devolution 3 Survival of the fittest 4 See also 5 References 6 External links

[edit] Evolution as theory and fact

Main article: Evolution as theory and fact

Further information: Scientific Theory

See also: Theory vs. Fact

While evolution is a successful scientific theory, there are those that misunderstand this point to mean that evolution is unproven, incomplete, or liable to be proven wrong.^{[citation needed]} This misunderstanding has been succinctly put as "evolution is a theory and not a fact" with the tacit assumption that theories are less established than facts (and less well supported than other beliefs).^{[citation needed]} This is primarily due to confusion arising from using the word "theory" to signify "conjecture", "speculation", or "opinion". In science however, a theory is a model of the world (or some portion of it) that makes predictions that can be tested through controlled experiments.^{[citation needed]}

A second linguistic confusion has arisen around the word "fact". Fact is often used by scientists to refer to empirical data, objective verifiable observations. But fact is also used in a wider sense to include any hypothesis for which there is overwhelming evidence. In this usage "the sun is at the center of the solar system" and "objects fall due to gravity" are considered to be facts.^{[citation needed]}

Moreover the word evolution may refer to the observed fact, or it may refer to a theory which explains it. When "evolution" is used to describe a fact, it refers to the observations that populations of one species of organism do, over time, change into new, or several new, species. In this sense, evolution occurs whenever a new strain of bacterium evolves that is resistant to antibodies that had been lethal to prior strains. Another clear case of evolution as fact involves the hawthorn fly.

When "evolution" is used to describe a theory, it refers to an explanation for why and a model of how evolution occurs. An example of evolution as theory is the modern synthesis of Darwin and Wallace's theory of natural selection and Mendel's principles of genetics. As with any scientific theory, the modern synthesis is constantly debated, tested, and refined by scientists. There is an overwhelming consensus in the scientific community that it remains the only robust model that accounts for the known facts concerning evolution.^{[citation needed]}

[edit] Evolution, complexity, and devolution

One of the most common misunderstandings about evolution is that one species can be "more highly evolved" than another; that evolution is necessarily progressive and/or leads to greater "complexity", or that its converse is "devolution".^[4] Evolution is a non-directional process in the sense that it does not proceed toward any ultimate goal. Rather, evolution acts to optimize organisms to the conditions of their environment, whatever they might be, through the process of natural selection. Thus, evolution provides no assurance that later generations will be more complex than earlier generations, a fact that applies equally to human complexity and intelligence as it does to all other organisms on Earth today and in the past. The claim that evolution results in directional progress is not part of modern evolutionary theory; it derives from earlier belief systems which were held around the time when Darwin formulated his ideas.^{[citation needed]}

In many cases evolution does proceed in the direction of increasing complexity. The earliest organisms were maximally simple life forms. Evolution caused life to become more complex, since becoming simpler wasn't advantageous; indeed it was likely impossible since organisms of any lower complexity would be too simple to carry out basic life functions. Virtually the only avenues open for evolution in the earliest epoch of life’s history was toward more complex and specialized forms. Since then, evolved complexity is a pattern that has occurred again and again in numerous lineages since it produces more specialized forms that are capable of exploiting environmental niches more effectively than competitors. Indeed, specialization through increased complexity allows an organism to define its own niche and evolve to it, thus also increasing biodiversity.^{[citation needed]}

But complexity is not an ultimate goal of evolutionary processes, and the evidence supporting this abounds.^{[citation needed]} Bacterial forms have remained comparatively simple over 3.8 billion years of evolution even though numerous forms have evolved and specialized to a variety of environments using diverse metabolic pathways. In these cases, complexity was not selected for even though substantial evolutionary change occurred. Simple organisms that rapidly metabolize energy rich nutrients available in the environment are optimal forms that dominate the biosphere and the cycling of elements in it. Among eukarya much greater levels of complexity have evolved, but these organisms represent the smaller portion of the biomass on earth. Thus, evolution toward complexity is the exception and not the norm.^{[citation needed]}

There are numerous examples of organisms evolving towards simpler forms. Vestigial structures constitute one line of evidence of lessening complexity evolving among eukarya.^{[citation needed]} Pythons have a vestigial pelvis that is detached from the vertebra and essentially floats in the abdominal cavity. This structure is functionless and degenerate from a functioning pelvis, with legs, in a previous ancestor.^{[citation needed]} The Mexican tetra (Astyanax mexicanus) has evolved from a previous sighted ancestor into a blind form. While the animal retains a rudimentary eye, the nerves and retina are degenerate and functionless.^[5] The human appendix is a degenerate form of the caecum found in a wide variety of herbivorous vertebrates. In these animals, the caecum is a significant organ that functions to digest cellulosic plant material. In humans and hominoid apes, changes in diet have favored its degeneration. In each instance, natural selection has acted to produce decreasing complexity over time because the maintenance of useless organs represents a drain on the organism’s energy resources and is thus subject to negative selective pressure.^[6]

Similarly, horses evolved from morphologically more complex ancestors with five toes on their feet. Over time, the fossil record shows a progression to reduced complexity that has produced the single toe (hoof) observed today. In the case of this animal, a simpler design is superior for the conditions under which it must survive.^{[citation needed]} Many parasitic and symbiotic species have evolved simpler forms from more complex to the point that they are incapable of existing outside the bodies of their hosts or symbionts. In these cases, reduced complexity offers a selective advantage but comes with the cost of surrendering independence.^{[citation needed]}

There is no guarantee that any particular organism existing today will become more complex in the future. In fact, natural selection will only favor increasing complexity if it increases an organism’s chance of survival and ability to produce viable offspring that live long enough to themselves reach sexual maturity. The same mechanism will also favor lower complexity in traits if that confers a selective advantage in the organism's environment.^[7]

[edit] Survival of the fittest

It is often misreported that natural selection is a case of survival of the fittest. While sometimes mistakenly attributed to Charles Darwin, this phraseology was coined by Herbert Spencer in reference to his philosophical extensions of evolution as a guiding principle and mechanism of society and culture (see Social Darwinism). However, biological evolution relies not on objective "fitness" but adaptation to biological niches that develop within the broader context of an ecosystem.^{[citation needed]} A "highly-evolved" species is one that is uniquely adapted to a particular context and even small changes in such cause dramatic changes in the evolutionary history of such species.^{[citation needed]} As such, the species that exhibit the most longevity are not necessarily those that are the "victors" of evolution. Indeed, it is single-celled organisms that have been in existence as organisms for the longest and are likely to be around long after the crown eukaryotes are extinct.^{[citation needed]} This misunderstanding of "evolutionary progress" may be in part due to a teleological imposition on evolutionary theory, one that is most clearly illustrated by considering the fallacy of devolution.^{[citation needed]}

[edit] See also

• Objections to evolution

[edit] References

[edit] External links

• TalkOrigins.org – Five Major Misconceptions about Evolution