Co-evolution
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In biology, co-evolution is the mutual evolutionary influence between two species. Each party in a co-evolutionary relationship exerts selective pressures on the other, thereby affecting each others' evolution. Co-evolution includes the evolution of a host species and its parasites, in examples of mutualism evolving through time. Few perfectly isolated examples of evolution can be identified. Evolution in response to abiotic factors, such as climate change, is not coevolution (since climate is not alive and does not undergo biological evolution). Evolution in a one-on-one interaction, such as that between a specialized host-symbiont or host-parasite pair, is coevolution. But many cases are less clearcut: a species may evolve in response to a number of other species, each of which is also evolving in response to a set of species. This situation has been referred to as "diffuse coevolution". And, certainly, for many organisms, the biotic (living) environment is the most prominent selective pressure, resulting in evolutionary change.
Examples of co-evolution include pollination of orchids by hummingbirds. These species co-evolve because the birds are dependent on the flowers for nectar and the flowers are dependent on the birds to spread their pollen so they can reproduce. The evolutionary process has led to long-billed birds and deep flowers.
Co-evolution also occurs between predator and prey species as in the case of the rough-skinned newt, Taricha granulosa, and the common garter snake, Thamnophis sirtalis. In this case, T. granulosa newts produce a potent nerve toxin that concentrates in their skin. T. sirtalis garter snakes have evolved resistance to this toxin through a set of genetic mutations, and prey upon the newts. The relationship between these animals has resulted in an evolutionary arms race that has driven toxin levels in the newt to extreme levels. (see Red Queen).
Co-evolution does not imply mutual dependence. The host of a parasite, or prey of a predator, does not depend on its enemy for persistence.
Co-evolution is also used to refer to evolutionary interactions between and even within molecules in the field of molecular evolution (for example, between hormones and receptors). This usage has existed at least since the term "molecular coevolution" was coined by Gabriel Dover in 1984. Dover claims that there is a third force in evolution, operationally distinct from natural selection and neutral drift, which he termed "molecular drive". According to Dover it explains biological phenomena that natural selection and neutral drift alone cannot explain, such as the 700 copies of a ribosomal RNA gene and the origin of the 173 legs of the centipede [1].
The existence of mitochondria within cells is an example of co-evolution. Scientists for many years thought mitochondria looked like bacteria under the microscope, but only with DNA research was their history more fully understood. Mitochondria have a different DNA sequence than that of the host cell in which they reside, and in fact do have genetic markers of bacteria. In addition, they have striking similarities to the bacteria which cause typhus. These bacteria cause much damage because of their ability to burrow through a cell wall. While mitochondria do not possess (or no longer possess) this ability, it leads to some interesting theories dating back to the 'primeval ocean'. One could envision a co-dependent relationship between primitive cells and bacteria that eventually merged due to mitochondria's ability to burrow into the cell (without killing it) — forming a more permanent mutally beneficial partnership. With its own DNA signature, the mitochondrion still has the ability to follow its own evolutionary path — separate from the host cell's DNA — but the co-dependent nature of co-evolution should restrict its mutations to those not detrimental to the host.
Co-evolutionary algorithms are also a class of algorithms used for generating artificial life as well as for optimization, game learning and machine learning. Pioneering results in the use of co-evolutionary methods were by Daniel Hillis (who co-evolved sorting networks) and Karl Sims (who co-evolved virtual creatures).
In his book The Self-organizing Universe, Erich Jantsch attributed the entire evolution of the cosmos to co-evolution.
In astronomy, an emerging theory states the co-evolution of galaxies and black holes[2].
[edit] Bibliography
- Michael Pollan The Botany of Desire: A Plant's-eye View of the World Bloomsbury ISBN 0-7475-6300-4 Account of the co-evolution of plants and humans
- Dawkins, R. Unweaving the Rainbow and other books.
- Geffeney, Shana L., et. al. “Evolutionary diversification of TTX-resistant sodium channels in a predatorÂ-prey interaction”. Nature 434 (2005): 759–763.
