Convergent Evolution
From SkepticWiki
[edit] Definition
[edit] Discussion
We can see evidence for convergent evolution both on the smallest and on the largest scale. At the smallest scale, there is the simple fact that experiments in the laboratory on the evolution of bacteria are highly reproducible, as are computer simulations of evolution: given the same situation, we do indeed get convergence, again and again, on the same sort of solution.
On the larger scale the theory of evolution predicts that when we use tools such as comparative morphology and molecular phylogeny to find the affinities of organisms, we should find that the degree of similarity we find between species should reflect biogeography rather than superficial similarities related to ecological function: and this indeed what we find.
Some brief examples: the marsupial wolf is (or rather was) closely genetically to other Australian marsupials[1] than to wolves, despite some striking if superficial similarities[2]; South American anteaters are closer genetically to sloths[3] than they are to aardvarks, despite sharing with them a number of adaptations for eating colonial insects; the Australian gliders are closer genetically to other Australian marsupials[4] than to the American flying squirrels, although superficially the two are so similar that they are often confused[5]; the Old World vultures are closer genetically to Old world hawks and eagles than to New World vultures[6].
We should usually expect not to find convergence of different lineages to the same solution within the same geographical area, because one would very likely fill the ecological niche first, from which position it could outcompete any upstart competitors. There is, however, one case in which we might expect to find different lineages living in the same place converging on the same superficial appearance: this is in the case of mimicry. A mimic must live in the same place as its model, or mimicry is pointless; as the mimicry is not the result of a functional adaptation to pursue the same lifestyle as the model, the problem of two species trying to occupy the same ecological niche does not arise. As a result, not only can a mimic converge on the appearance of a model, but unrelated mimics can separately converge on the appearance of the same model.
