Genetic Equidistance

The Genetic Equidistance phenomenon was first found by evolution biologist E. Margoliash in 1963 and published in PNAS, 50: 672-679. Margoliash wrote: "It appears that the number of residue differences between cytochrome C of any two species is mostly conditioned by the time elapsed since the lines of evolution leading to these two species originally diverged. If this is correct, the cytochromes c of all mammals should be equally different from the cytochromes c of all birds. Since fish diverges from the main stem of vertebrate evolution earlier than ether birds or mammals, the cytochromes c of both mammals and birds should be equally different from the cytochromes c of fish. Similarly, all vertebrate cytochrome c should be equally different from the yeast protein." For example, the difference between the cytochrome C of a carp and a frog, turtle, chicken, rabbit, and horse is a very constant 13% to 14%. Similarly, the difference between the cytochrome C of a bacterium and yeast, wheat, moth, tuna, pigeon, and horse ranges from 64% to 69%. The Genetic Equidistance phenomenon is the most remarkable result of molecular evolution. The molecular clock explains the equidistance phenomenon by assuming a constant mutation rate in different lineages. But the constant mutation rate assumption has been falsified by numerous independent experiments and few evolution biologists now believe a constant clock (see the Wiki page on molecular clock). So, there is at present no scientific explanation for the equidistance phenomenon. The constant clock interpretation of the equidistance phenomenon is merely a restatement of the fact of equidistance and is hence a tautology rather than a real explanation. The question remains unsolved: how can vastly different species with vastly different mutation rates and generation times all end up being equally different from an outgrop? How can yeast and human be equally different from bacteria when the lineages leading to yeast and to human clearly do not have the same mutation rate and generation time? So, the Genetic Equidistance phenomenon is a challenge to the present evolution theory because the theory cannot explain it.

ee also

* Neutral theory of molecular evolution

References

* Ayala, Francisco J. (1999): Molecular clock mirages. "BioEssays" 21(1): 71-75. [http://www3.interscience.wiley.com/cgi-bin/abstract/60000186/ABSTRACT?CRETRY=1&SRETRY=0 HTML abstract]
* Bromham, L., and Penny, D. (2003). The modern molecular clock. Nat Rev Genet 4, 216-224.
* Denton, M. (1986). Evolution: a theory in crisis (Chevy Chase, MD: Adler & Adler).
* Fitch, W. M., and Margoliash, E. (1967). Construction of phylogenetic trees. Science 155, 279-284.
* Hedges, S. B. (2002). The origin and evolution of model organisms. Nat Rev Genet 3, 838-849.
* Kumar, S. (2005). Molecular clocks: four decades of evolution. Nat Rev Genet 6, 654-662.
* Margoliash, E. (1963). Primary Structure And Evolution Of Cytochrome C. Proc Natl Acad Sci U S A 50, 672-679.
* Nei, M., and Kumar, S. (2000). Molecular evolution and phylogenetics (New York: Oxford University Press).
* Zuckerkandl, Emile & Pauling, Linus B. (1962): Molecular disease, evolution, and genetic heterogeneity. "In:" Kasha, M. & Pullman, B. (editors): "Horizons in Biochemistry": 189–225. Academic Press, New York.

External links

* [http://home.wxs.nl/~gkorthof/kortho37.htm The Neutral Theory of Molecular Evolution]
* [http://www.sciencedaily.com/releases/2007/02/070210170623.htm Professor Jeffrey H. Schwartz challenges molecular clock]
* [http://www.rtis.com/nat/user/elsberry/evobio/evc/argresp/sequence.html Explaining the molecular equidistance by the molecular clock]