Thursday, March 25, 2010
Convergent and Parallel Evolution
Divergent evolution is the most well known form of evolution - the evolution of one species into two distinctively different species. However, on page 91 Coyne mentions a wholly different form of evolution that caused the formation of similar body plans and physiological traits between succulents in North America and succulents in Old World deserts. This convergence to similar physical structures came as the result of similar environmental conditions and niches. Two modes of evolution that work in such a manner are Parallel Evolution and Convergent Evolution. What is the difference between these two forms of evolution? Provide examples of each.
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Parallel Evolution is the evolution of geographically separated groups in such a way that they show morphological resemblances (britannica). For example the marsupial mammals in Australia compared to the placental mammals found in places other than Australia. They are geographically separated but they have remarkably similar forms, some of the marsupials are even named for their placental counterparts. Parallel evolution occurs due to similar environmental pressures in different places acting on plants and animals to evolve in similar ways even though they are not related. The appearance of xylem vessels in the vascular tissue of unrelated plants such as Ephedra in gymnospermous division Gnetophyta and flowering plants in angiospermous division Anthophyta. Also Ephedra have double fertilization which was once thought to only be an angiosperm characteristic. These similarities are examples of parallel evolution because they do not have a known common ancestor, if they did it would not be parallel evolution (palomar.edu). Parallel evolution is about the adaptations that occur due to environmental pressures on two unrelated species that are in different types of environments, it is not about appearance but convergent evolution is when two distinct species with differing ancestors have very similar physical features due to having the same environmental circumstances. For example, the wings of all flying animals are very similar because that is the wing design that the laws of aerodynamics require for successful flight. Birds, bats and pterosaurs all developed wings separately yet they all ended up with similar wings even though they were at different times due to environmental pressures (science.jrank.org). Another example of convergent evolution is that fish that have the same environment of frigid waters have adapted a kind of antifreeze composed of glycoproteins to allow them to live in the cole water. Fish in Antartica and in the Arctic have the same kind of antifreeze genes and proteins, convergent evolution because they are not related yet they have adapted in the same way because they are in the same type of environment (pbs.org).
ReplyDeletehttp://www.pbs.org/wgbh/evolution/library/01/4/l_014_01.html
http://www.britannica.com/EBchecked/topic/442817/parallel-evolution
http://waynesword.palomar.edu/convevol.htm
http://science.jrank.org/pages/2608/Evolution-Convergent.html