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What Is Convergent Evolution?

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  • 0:01 Uncommon Ancestors
  • 1:30 Body Stuctures
  • 4:11 Deciphering the Code
  • 5:20 Lesson Summary
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Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

It can be difficult to tell whether species are related just by looking at them. Organisms look and act the way they do because of ancestry, but similarities also arise because of similar environmental roles, as is the case with convergent evolution.

Uncommon Ancestors

Many species exhibit traits similar to each other because they're descendants of a single common ancestor. For example, apes and humans both have opposable thumbs because our ancestors from long ago also had this trait. Dogs are descended from wolves, so they also have very similar features, such as their ears, faces, and paws. These features are similar because they were passed down through many generations over thousands or millions of years.

Some species, however, have traits that look very similar, but the species are not related at all. Most often this occurs because these species live in similar environments and fill similar ecological roles. This natural selection that favors the same type of structure in different ancestors is called convergent evolution. To converge is to come together, so this term describes how the different species 'came together' with similar traits even though they are not evolutionarily related.

Body Structures

When organisms have similar traits because they come from a common ancestor, we call these homologous structures. 'Homo' means 'same,' and these traits come from the same ancestor even though the now present species may be different in other ways.

When species have similar traits because of convergent evolution, we call these analogous structures. An analogy is a likeness or comparison between two different things, so this is an appropriate term for similar structures that come from different ancestors.

Convergent evolution is actually a fairly common process. For example, many animals that are completely unrelated have wings and can fly. Bats, birds, insects, and even some fish have wings, and even though this structure serves the same function, the bones, wing coverings (such as feathers, scales, or hair), shapes, sizes, and location on the body are all quite different. In fact, a bat's wing is actually more closely related to a human arm than it is to even a bird's wing! These homologous structures (the bat wing and human arm) evolved from the same structure in a long-ago mammalian ancestor, and you can clearly see this when you compare the bones of each.

Another good example of an analogous trait derived through convergent evolution is the flipper. Animals such as seals and penguins both have flippers to help them navigate through their aquatic environments. However, seals are mammals, and penguins are birds, which are actually very closely related to reptiles. We can see how since these animals are not related at all, and that the flipper most likely evolved in both not from a common ancestor but because it was the best functional feature for the environment they inhabit.

While analogous traits may be most easily seen in animals, all organisms can exhibit convergent evolution. Many species of plants, fungi, and bacteria have analogous traits based on their environmental demands. For example, spines and thorns are similar structures on plants that often serve the same purpose - to inflict pain and protect the plant from predation. However, spines are modified leaves, while thorns are modified stems - again, two structures that are environmentally similar but evolutionarily quite different.

Analogous traits are also not limited to visual structures. Things like behavioral traits can also become similar through convergent evolution. For example, bird songs come in a wide variety of sounds, not just between different species but also between different flocks. However, some bird species that are quite unrelated can develop analogous song characteristics if they're held together in similar conditions for long periods of time, say in a lab setting. This indicates that even something like vocalizations may sometimes be more environmentally related than evolutionarily.

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