Not all species similarities are due to common ancestry. Species from different evolutionary branches may come to have similar characteristics due to sharing similar ecological roles. Natural selection results in similar evolution or at least similar features. This is known as convergent evolution and resultant similarities are called analogy rather than homology. (Taylor, 1999).
An example is the whale; it has a streamlined appearance similar to a fish as they evolved in the same environment. The whale is not a fish as its bone structure shows that it has ancestry common to mammals.(AP Biology, 2nd Ed. (Book Only), n.d.)
Another example of convergent evolution is the African crested rat and the hedgehog species Aterlerix pruneri and Hemiechinus. They are completely different species but have similar ways of protecting themselves involving toxin tolerance. The African crested rat coats its fur with saliva containg the toxin Ouabain obtained by chewing the bark of certain plants. They have evolved highly specialised hair shafts which soak up the saliva to increase the time it stays poisonous.…show more content… Convergent evolution can be distinguished from homologous evolution by examining the complexity of similar structures; the more complex, the less likely it is that they evolved independently. For example human and chimpanzee skulls consist of a fusion of many bones and are almost identical. It is therefore very unlikely that this similarity resulted from convergent evolution(Taylor,