Looking through squid shaped lenses

Posted 1 July 2013 by M. Wilson Sayres

Many times we utilize and study the products of evolution that result from species sharing a common history. For example, the reason we can use mice for studies of human diseases and medical treatments is that, because of shared ancestry, a mouse body and the set of mouse genes is similar enough to a human body and the set of human genes that both will develop similar diseases, and respond similarly to treatments.

There are other products of evolution that occurred independently, and are not the product of common ancestry. This is more likely to happen if a feature is useful in certain environments, but wasn't present in the common ancestor. For example, although a shark is a fish, and a dolphin is a mammal, both evolved sleek fins for gliding through the water (one of the many clues that they do not share a common ancestor is that the shark skeleton, like other fish, is structured so that a shark tail swims left to right, but a dolphin's skeleton is structured like that of other mammals, and as a result the dolphin tail swims up and down).

Left:Right - Great White Shark by Pterantula (Terry Goss)

Up:Down - Dolphin (Turisops truncatus) by Arnaud 25

This is what we call convergent evolution.

Convergent evolution:
The independent evolution of similar features in species of different lineages
- Reece et al., Campbell Biology (9th Edition)

Just as we can take advantage of shared evolutionary history to learn more about ourselves, we can also study cases of convergent evolution to learn more about, well, ourselves!

For example, eyes evolved multiple times throughout the evolutionary tree. Specifically, the eyes of squids evolved independently of ours, but function in very similar ways. Because of the similar function, squid eyes can be affected by disorders, like myopia (being near-sighted/short-sighted), that affect human eyes. By studying how the squid eye evolved, and how it develops now, scientists hope to make advances in understanding and treating eye disorders in humans. Emma Goodman put together a wonderful summary of this, "Eyevolution":

'Eyevolution' NESCent 2013 from Emma Goodman on Vimeo.

Evolution is awesome.

6 Comments

DS · 1 July 2013

This brings up a good point. Convergent evolution is more common in characters that are strongly selected on. For characters that are not selected on, convergence is due to chance alone. This may still occur in a few characters, but it is unlikely to obscure the phylogenetic signal in many different characters. This is why some characters, such as SINE insertions display such low levels of convergence and why they are ideal characters for phylogenetic inference. There are a large number of insertion sites, most of which are under no selective constraint. And of course there is virtually no character state reversal, since there is no know mechanism for removal of insertions. Therefore, the low level of homoplasy observed for these characters makes them ideal. Why can't creationists understand this?

Henry J · 1 July 2013

Why can’t creationists understand this?

Because they judge arguments primarily by how they feel about the conclusion? Other factors are considered only when no strong feelings are present regarding the conclusion.

Richiyaado · 1 July 2013

Maybe they just don't see it because their eyes are bad.

Robert Byers · 2 July 2013

This comment has been moved to The Bathroom Wall.

Henry J · 2 July 2013

One starts by reading a textbook.

M. Wilson Sayres · 2 July 2013

This:

Henry J said: One starts by reading a textbook.