Co-evolution
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In Biology, co-evolution is the mutual evolutionary influence between two species that become dependent on each other. Each party in a co-evolutionary relationship exerts selective pressures on the other, thereby affecting each others' evolution. Coevolution 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: essentially all evolution is co-evolution.
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 (see Red Queen).
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].
Bibliography
- Michael Pollan The Botany of Desire: A Plant's-eye View of the World Bloomsbury ISBN 0747563004 Account of the co-evolution of plants and humans
- Dawkins, R. Unweaving the Rainbow and other books.