Divergent evolution
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Divergent evolution occurs when two or more biological characteristics have a common evolutionary origin but have diverged over evolutionary time. This is also known as adaptation or adaptive evolution. These characters can be observable structures from different species or they can be molecular entities, such as genes or pathways. This is a kind of relationship observed in evolutionary biology.
Divergent evolution can be seen in some higher-level characters of structure and function that are readily observable in organisms. For example, the vertebrate limb is one example of divergent evolution. The limb in many different species has a common origin, but has diverged somewhat in overall structure and function.
Alternatively, "divergent evolution" can be applied to molecular biology characteristics. This could apply to a pathway in two or more organisms or cell types, for example. This can apply to genes and proteins, such as nucleotide sequences or protein sequences that derive from two or more homologous genes. Both orthologous genes (resulting from a speciation event) and paralogous genes (resulting from gene duplication within a population) can be said to display divergent evolution. Because of the latter, it is possible for divergent evolution to occur between two genes within a species.
Divergent evolution and convergent evolution are distinct. In the case of divergent evolution, similarity is due to the common origin, such as divergence from a common ancestral structure or function has not yet completely obscured the underlying similarity. In contrast, convergent evolution arises when there are some sort of ecological or physical drivers toward a similar solution, even though the structure or function has arisen independently, such as the different characters converge on a common, similar solution from different points of origin.
[edit] Usage
The usage of this term and other related terms can vary slightly from one researcher to the next. Furthermore, the actual relationships might be more complex than the simple definitions of these terms allow. "Divergent evolution" is most commonly meant when someone invokes evolutionary relationships and "convergent evolution" is applied when similarity is created by evolution independently creating similar structures and functions. The term parallel evolution is also sometimes used to describe the appearance of a similar structure in closely related species, whereas convergent evolution is used primarily to refer to similar structures in much more distantly related clades. For example, some might call the modification of the vertebrate limb to become a wing in bats and birds to be an example of parallel evolution. Vertebrate forelimbs have a common origin and thus, in general, show divergent evolution. However, the modification to the specific structure and function of a wing evolved independently and in parallel within several different vertebrate clades. Also, it has much to do with humans and the way they function from day to day.
In complex structures, there may be other cases where some aspects of the structures are due to divergence and some aspects that might be due to convergence or parallelism. In the case of the eye, it was initially thought that different clades had different origins of the eye, but this is no longer thought by some researchers. It is possible that induction of the light-sensing eye during development might be diverging from a common ancestor across many clades, but the details of how the eye is constructed--and in particular the structures that focus light in cephalapods and vertebrates, for example--might have some convergent or parallel aspects to it, as well. (See Gehring reference below and other researchers cited in that research field).
A good example of divergent evolution is the Darwin's finches, which has now over 80 varieties which all diverged from one original species of finch. (John Barnes)
[edit] References
- Schneider RA. Developmental mechanisms facilitating the evolution of bills and quills. J Anat. 2005 Nov;207(5):563-73.
- Murphy WJ, Pevzner PA, O'Brien SJ. Mammalian phylogenomics comes of age. Trends Genet. 2004 Dec;20(12):631-9.
- Good JM, Hayden CA, Wheeler TJ. Adaptive Protein Evolution and Regulatory Divergence in Drosophila. Mol Biol Evol. 2006 Mar 14
- Yoshikuni Y, Ferrin TE, Keasling JD. Designed divergent evolution of enzyme function. Nature. 2006 Feb 22
- Rosenblum EB. Convergent evolution and divergent selection: lizards at the white sands ecotone. Am Nat. 2006 Jan;167(1):1-15.
- De Grassi A, Lanave C, Saccone C. Evolution of ATP synthase subunit c and cytochrome c gene families in selected Metazoan classes. Gene. 2006 Feb 3;
- Gehring WJ. Historical perspective on the development and evolution of eyes and photoreceptors. Int J Dev Biol. 2004;48(8-9):707-17.
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