Zebrafish are a popular model animal, for example, but their eye-brain wiring is very different from that of a human. Modern fish do not have this type of eye-brain connection. This has allowed us to discover something that we did not know until now.
The going theory had been that this connection first developed in terrestrial creatures and, from there, moved to humans, where scientists believe it helps with our depth perception and 3D vision. But it seems that this is not what happened.
Previous connection to land animals
According to this new study, published in Science, this type of eye-brain connection predates animals that live on land. To carry out the study, Researchers used an innovative technique to view the nerves that connect the eyes to the brain in several different fish species.
In a zebrafish, each eye has a nerve that connects it to the opposite side of the fish's brain. That is, one nerve connects your left eye to the right hemisphere of your brain and another nerve connects your right eye to the left side of your brain. The other, more "older" fish do things differently. They have what are called ipsilateral or bilateral visual projections. Here, each eye has two nerve connections, one on each side of the brain, which is also what humans have.
Then the brain gar fish. In this microscope image, the left hemisphere of the brain lights up in green and the right hemisphere in magenta. However, at the bottom of the image, you can see nerves of both colors connecting to both hemispheres. This shows that both of the gar's eyes are connected to both sides of its brain, just like a human's eyes are.
According to the authors:
We are increasingly finding that many things that we think evolved relatively late are actually very old. We learn something about ourselves when we look at these strange fish and understand how old our own body parts are.
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The news
The sophisticated network of nerves that connect the eyes to the brain evolved 100 million years earlier than thought
was originally published in
Xataka Science
by
Sergio Parra
.