Explain what is meant by the terms analogy and homology with specific examples.

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Payal Khullar | College Teacher | (Level 2) Associate Educator

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It is quite common to see certain traits or characters that are strikingly similar in totally different species of organisms (in case of both plants and animals), like two eyes, four limbs, etc.

When these similar traits or features occur in different species because they supposedly evolved from a common ancestor, the condition is called as homology and such features are called as homologous features. For example, the four limbs of different species like humans, dogs, crocodiles, bats, mice etc. have similar structures. It is a possibility, then, that all these tetrapods were actually the progeny of a common ancestor who also had four limbs. In the course of evolution, these developed slight variations.

In case of an analogy, similar traits occur not because of common ancestry, but instead because of convergent evolution. Now if we consider the wings of a bat and a bird, we will observe remarkable differences in their anatomical structures, which is how one can conclude that though wings of both bats and birds perform a common function (i.e. flight), they are not derived from a common ancestor. It is a possibility that both faced similar environmental stress that needed them to have a flight mechanism. And so they underwent a similar but independent lineage “pattern” or convergent evolution.

Both Homology and Analogy are significant to the study of Evolutionary Biology. As we know, Charles Darwin supported his theory of Natural Selection and Common Ancestry taking into account homologous traits in different species.