A new study from Northwestern University and the Colleges of Claremont McKenna, Scripps, and Pitzer suggests that not the limbs were those that drove fish out of the sea and onto land. It was improved vision.
Researchers suggest that, due to this improved vision, they were able to see the abundance of prey on land which prompted them to evolve limbs so that they could get out of the water. Also, this improved vision might be the source of prospective cognition in humans, namely the ability to weigh out all options and make decisions for the future.
For the research, the scientists studied 59 fossils which originated both before and after the water-to-land transition, as well as some that were alive during the transition. They took measurements of the eye sockets and of their heads.
Dr. Malcolm MacIver, neuroscientist and engineer, and Dr. Lars Schmitz, evolutionary biologist and paleontologist, were the ones who discovered that eyes tripled in size during the period when transition started.
Afterwards, they designed computer simulations of several visual environments, such as clear water, murky water, or air. They noticed that an increase in eye size was beneficial for vision through air and not water.
Before the transition, the average size of the orbit was 13 millimeters. Then, it increased to 36 millimeters on average. Also, the eyes changed their location, from the sides of the head to the top of the head.
An expansion of the field of vision might have been the thing that prompted the development of larger brains in land vertebrates. This allowed them to plan their actions beforehand, instead of only reacting.
Thus, 385 million years ago, just before the transition of vertebrates from an aquatic environment to land, researchers discovered an increase in the visual capabilities of these animals. The researchers hypothesized that it was the amount of easy meals that they saw on land which drove them to get out of the sea.
Also, they said that eyes of a bigger size were not needed in water, since fish only need to see what is directly in front of them. Instead, larger eyes are much better when the animal sees through air. Thus, they first evolved the eyes, and then evolved the limbs to leave the waters and go on land.
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