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Homologous organisms are everywhere. This lesson defines homology and offers different examples of homology. Take the quiz that follows to demonstrate your understanding of this topic.

Homology

Have you ever thought about how similar or different living organisms are to each other? For instance, maybe you thought that the wings of birds and bat or the fins on sharks and dolphins really look similar to one another. This thought process falls under the umbrella of homology. Homology is the study of similarities between organisms to determine common ancestors based on genes, physiology or development. The structures or genes that fall under homology are referred to as being homologous.

Examples of Homology

Let’s look at the wings that I just mentioned along with the front limbs of some other animals with which you may not have associated those wings. The front limbs on bats, birds, humans and lizards are all homologous because they are composed of the same types of bones. The basic structure of these limbs are made up of the radius, ulna and humerus.

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This provides some proof to the possibility that we and the other animals mentioned all came from a common ancestor years ago. I bet you are thinking that it is hard to believe that you and the bat that you never want to encounter could have a common ancestor, but homology says otherwise. Homology is not just found in physical structures or just in animals, so let’s look at some other examples.

The humerus, ulna and radius
Picture showing the bones of the forelimbs

An example of homology that has really been interesting to discover has to do with the genes that control the development of the eyes. Almost all animals – whether we are talking about dogs, humans, flies or birds – have the same type of gene that codes for the creation of our eyes. Relatively recently, geneticists even took a version of the gene that codes for eyes in humans and inserted it into flies, and it resulted in the development of eyes in the flies.

This has been repeated between many other animals as well now. The fact that this is even possible means that the gene had to have come from an ancestor that is shared by any animal in which the gene works.

The eyes of animals are an example of homology
Clipart of eyes

Plants provide another example of homology.

Plant lovers usually describe their favorite plant based on the flowers and/or leaves. While we decide which ones we like based on the differences that we see, there is a lot of similarity between the leaves of plants. The structure of the leaves may look a little different, but these are modifications that they adapted from leaves of the same ancestor. In the case of a cactus plant, the leaves are shaped like needles to hold in moisture which it needs to help produce food.

A Venus fly-trap has leaves that act as jaws to catch the food it needs. Even the pine tree that you may be thinking about for the holidays has thin, pointy leaves that help them carryout photosynthesis to produce food.

Venus flytrap uses its leaves to catch insects
Picture of Venus flytrap with insect

Lesson Summary

Homology looks at the similarities that exists in living organisms in order to determine common ancestry. The similarities can be in the genes, physical appearance or function of structures.

Examples of this include the front limbs of birds, bats, humans and lizards since they have the same structure. Another example that we discussed is the gene that controls the development of eyes in almost all animals including insects. The gene is so homologous that it can be interchanged between species and still cause development of an eye.

The last example we looked at is the leaf of a plant. While plants may differ in many ways, the leaves are homologous since they have the same purpose but just a different way of going about serving that purpose.

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