Homology vs. Homoplasy

Homology and Homoplasy of Bat and Bird Wings
Gray's Anatomy Book/Getty Images

While the evolution terms homology andhomoplasy may sound similar, they are different in their meanings.

What Is Homology?

The term homology refers to structures on two or more different species that are similar or the same that came from a common ancestor of the species.

What Is Homoplasy?

Homoplasy, on the other hand, describes a characteristic that two or more different species have in common that was not inherited from their recent ancestor.

Instead, a homoplasy would have evolved independently usually due to natural selection in similar environments or filling the same type of niche as the other species with that trait.

Divergent and Convergent Evolution

Homology is a product of divergent evolution. The two species were once the same species at the point where they have a most recent common ancestor. Over time, individuals in the population evolved through either some type of selection or isolation from the rest of the population. The species, even though they diverged at that point, still retain some of the characteristics of the common ancestor. These are the homologies.

Convergent evolution is the origin of a homoplasy. These similar traits evolved independently of each other and are not found in the common ancestor of the two species being examined. Instead, each species evolved the trait after diverging and becoming separate species.

Some causes of homoplasies are species living in similar environments, filling the same types of niches, or through natural selection.

Examples of Homology and Homoplasy

The wings of birds and bats are an example of both homology and homoplasy. The bones within the wings are homologous structures. They have the same bone structure with a type of breast bone, large upper arm bone, two forearm bones, and what would be hand bones.

In fact, these structures are also homologous in humans as birds, bats, and humans all share the same common ancestor.

The wings themselves are the homoplasies. Obviously, humans do not have wings. This means wings was not a characteristic of the common ancestor and cannot be homologous. Instead, through natural selection, bats and birds evolved wings to fill a niche and survive in their respective environments. Since the characteristic was derived after they diverged, they are considered homoplasies.

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Scoville, Heather. "Homology vs. Homoplasy." ThoughtCo, Apr. 13, 2017, thoughtco.com/homology-vs-homoplasy-1224821. Scoville, Heather. (2017, April 13). Homology vs. Homoplasy. Retrieved from https://www.thoughtco.com/homology-vs-homoplasy-1224821 Scoville, Heather. "Homology vs. Homoplasy." ThoughtCo. https://www.thoughtco.com/homology-vs-homoplasy-1224821 (accessed March 22, 2018).