Homologous organs are same origin but different function

The definition of homologous organs is that they are organs from different species that have a common evolutionary origin and a similar basic structure although they may or may not subsequently have different functions and an equally different appearance (at the end of the article there is a summary table). This phenomenon is called homology and is the subject of study in evolutionary biology.

IndexExample of homologous organsHomologous organs in plantsAnalogous organsSummary of homologous organs and difference with analogous organs

That said, throughout the article we are going to illustrate it to make it clearer.

It is worth clarifying that homology not only refers to homologous organs but this concept also applies to homologous structures and even to homologous genes that will not be the subject of this article.

Example of homologous organs

What do the arm of a human being and the wing of a bird have in common? What if we add the paw of a dog and the fins of a whale?

In all these cases, the base is built on the same pattern, on a structure of similar bones. And, after an evolutionary analysis, it has been observed that they derive from a common ancestor that had five fingers. Currently, they have them (the fingers) at some point in their life cycle, in a similar position although with a different appearance to develop a different function.

In the case of the human being to grab objects, in the case of the dog to support and walk, in the case of the bird to fly and in the case of the whale to swim; They are different functions of a homologous organ, the hand and its fingers.

In some they have been lengthened, others have been shortened, or they are articulated differently or they are fused or elongated as in the case of birds, and therefore show the different appearance that the homologous organs have .

Homologous organs. From Волков Владислав Petrovich (Vladlen666); translation by Angelito7 – file:Homology vertebrates.svg, CC0, https://commons.wikimedia.org/w/index.php?curid=30073361

In the previous example, we observed that the chosen species continued to maintain the five fingers, but we also commented that in the adult stage they did not have to maintain them.

For example, this is the case of the following image where the human hand (I) is compared with the forelimbs of the dog (II), the pig (III), the cow (IV), the tapir (V) and the horse. (SAW). In all these cases, we can observe a similar adult base structure, with a different function, a different appearance (different number of fingers) and a common origin (during embryonic development they have five fingers, it does not appear in the image).

Homology of the hand to the forelimbs (1870). I Man. II Dog. III Pig. IV Cow. V Tapir. VI Horse.r Radio. u Ulna. a scaphoid b Lunar. c Cuneiform. d Trapeze. e Trapezoid. f Magnum. g Uncinate. p Pisiform


Homologous organs derive from a specific organ of a common ancestor, although they may later have led to very different functions and appearance thanks to a so-called divergent evolution due to the evolutionary pressure of the environment in which they live.

Another example of homologous organs is found in insects. The same common structure has given rise to the flying wings of dragonflies, the pair of hard wing covers (elytra) of beetles, and in flies a second pair of wings that serve to maintain balance.

Homologous organs in plants

Homology is not something that is present only in animals. In plants we also find homologous organs that have a common origin, with a similar basic structure but different appearance and function.

A fairly clear and easy to see example happens in succulent plants. The leaves have evolved into water storage structures such as Aloe vera or into defensive structures such as spines.

In the ocotillo in the image, the spines come from the modified petiole of the leaves. An example of an analogous organ (same origin, same structure, different appearance and different function) Miskatonic assumed (based on copyright claims). – CC BY 2.5

In other species such as carrots the root has become a thickened root or in potatoes where tubers appear that are also modified roots.

Analogous organs

The opposite of homologous organs are analogous organs, which are those that are similar to each other with a very similar or the same function but have a different structure and evolutionary origin. We will see them in more depth in another article.

Summary of homologous organs and difference with analogous organs


Homologous organs

Analogous organs







Basic structure



Evolutionary origin

Common with divergent evolution

Different with convergent evolution

Explanatory table of the differences between homologous and analogous organs.

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