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In nature, animals look like one another for different reasons. Two beetles of the same species might look alike because they inherited their yellow and black spots from their parents. On the other hand, two flying animals, such as a bird and a bat, also appear similar to each other. The similarity between the beetles is inherited but the similarity between the bird and the bat is not. The similarity between the bird and the bat is due to evolution.
In birds, the Little Auk of the north Atlantic and the diving petrels of the southern oceans are remarkably similar in appearance and habits. Both Old World vultures and New World vultures have featherless necks and heads [link widoczny dla zalogowanych], search f
The skeletons of humans, whales, lizards, and birds are strikingly similar [link widoczny dla zalogowanych], despite the different lifestyles of these animals and the different environments they inhabit. Bone by bone, the similarity of these animals can be observed in every part of the body, including the limbs, yet a person throws a ball, a whale swims, an alligator shuffles, and a bird flies. Each of these animals is framed of bones that are different in detail but similar in general structure and relation to each other.
At first glance, many traits and structures that seem dissimilar are actually homologous but some that seem homologous are not. The wings of a bird and those of a bat might appear to be homologous but are, in fact, analogous. Analogous traits or structures are those that evolve independently in organisms that are not closely related as a result of having adapted to similar environments or niches through a process known as convergent evolution.
Consider the teeth of the beaver and the elephant. The gnawing front teeth of the beaver and the tusks of the elephants are both basically incisor teeth. While inherited in a basic form from an ancestor common to the beaver and the elephant, these teeth have been greatly modified by evolutionary mechanisms into the seemingly dissimilar teeth we see today in the beaver and the elephant.
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The Molecular Record of Evolution
The Fossil Record of Evolution
Charles Darwin and His Theory of Evolution
Convergent Evolution in Action
Similarities Derived From a Common Ancestor
Examples of convergent evolution abound in the animal kingdom. Several mammal groups have independently evolved prickly protrusions of the skin or spines. These include echidnas (monotremes), hedgehogs (insectivores), and porcupines (rodents). Claws and long, sticky tongues that allow them to open the nests of ants and termites are the analogous structures that mark mammals loosely grouped as anteaters. The anteater group encompasses four species of true anteaters, eight species of pangolin, four species of echidna [link widoczny dla zalogowanych], the African aardvark, and the Australian numbat.
Different animals wind up with the same sort of limb inherited from a common ancestor, just as cousins might inherit their hair color from their grandfather.Over time, a trait or structure inherited from a common ancestor may be changed and adapted taking on a different structure and function.
Convergent Evolution Produces Analogous Traits
Evolutionary biologists regard such similar traits and structures as being homologous and have concluded that such similarities are best explained by descent from a common ancestor. Comparative anatomists investigate such homologies, working out relationships from degrees of similarity. Their conclusions provide valuable inferences into the details of evolutionary history, inferences that can be tested by comparison with the sequence of ancestral forms in the fossil record and through cladistic analysis.
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