Claremont, Calif. (March 7, 2017) — New research by Assistant Professor of Biology Lars Schmitz suggests that enlarged eyes and expanded visual range in our ancient aquatic ancestors happened before their evolutionary leap from water to land, about 385 million years ago, and was a critical factor in how our brains developed. Schmitz and Professor Malcolm MacIver of Northwestern University and their team’s study, “Massive Increase in Visual Range Preceded the Origin of Terrestrial Vertebrates,” is published today in Proceedings of the National Academy of Sciences. The publication is accompanied by a three-minute animation that presents their findings with humor and clarity.
This unique interdisciplinary partnership, Schmitz, an evolutionary biologist and paleontologist, and MacIver, an engineer and neuroscientist, spent a year testing the hypothesis that our fish ancestors’ move to land expanded their vision and, in turn, their brains. Their studies also reveal new clues about why fish came onto land in the first place.
The two scientists, from distinctly different disciplines, at first seem an unlikely pair.
MacIver had built the “Buena Vista hypothesis,” which postulates that how far a creature can see influences its thinking—if you can see ahead, then you can plan ahead. “A critical step for testing this hypothesis would be to look at when life comes to land,” said Schmitz.
According to Schmitz, there are little explored fossils that document this transition fairly well. But MacIver’s expertise did not include fossils. So, he Googled “fossils + scleral rings” (the eye bones that sometimes are preserved) and found Schmitz.
Turns out, in 2012 they were going to the same scientific conference in San Francisco and met up in a bar. MacIver laid out his ideas about prospective cognition and said he wanted to look at it in the framework of the fossil record.
“It was like two worlds colliding—different fields with different languages,” said Schmitz. “We learned from each other. What resulted was an integrated approach that goes across disciplines. I found that fascinating.”
Through video conferences, the pair coordinated their efforts. Schmitz analyzed fossil measurements for 59 fossil animals. Also critical to his research was a cast of a “fishopod” on display at the Raymond M. Alf Museum of Paleontology in Claremont. The fishopod, a Tiktaalik skeleton, documents the transition period between fish and four-legged animals; its eyes face up, showing the beginning enlargement of eye sockets.
Since eyes disintegrate over time and normally only the sockets remain in fossils, it was important to verify that eye size correlates to socket size. Student Olivia Carma from the W.M. Keck Science Department, a joint program of Claremont McKenna, Pitzer and Scripps colleges, helped measure eye dimension and socket size on present-day fish, looking at 79 different species. Her research helped support the correlation. “These data were crucial to our analysis,” said Schmitz
The enlargement of eyes is significant, Schmitz explained. Bigger eyes are almost worthless in water because their vision is largely limited to what’s directly in front of them. But larger eye size is very valuable on land. In evolution, “it often comes down to a trade off. Is it worth the metabolic toll to enlarge your eyes and socket? What’s the point? The point may have been to be able to search out prey on land,” he said.
By analyzing the fossil trees, Schmitz and MacIver found that the placement of the eyes from the side to the top of the head and the increase in eye size took place in aquatic creatures long before their fins evolved into limbs. “If you are at the surface and your eyes are up, like a crocodile, you are seeing things on land—a whole smorgasbord of tasty land dwellers. This was a game changer,” Schmitz said.
With their eyes tripled in size and sensory volume increased a million-fold, the creatures had a bigger window into the future—an advantage that may have favored the evolution of limbs from fins—and could plan ahead. “The first animal to figure out how to plan ahead instead of just reacting to a directly imminent threat or opportunity should have had a huge evolutionary advantage,” said Schmitz. Evolution would eventually lead to the ability to imagine lots of future states and think strategically, something called prospective cognition.
Schmitz hopes that his and MacIver’s findings will add to our grasp of evolution. “We can understand a biological structure from an engineering or physical perspective,” he said. “How does it work? How did complex structures evolve and how do they function in the environment? Understanding this helps us know how we were shaped and how our brain is wired.”
The research was funded by a National Science Foundation grant to MacIver and support from the W. M. Keck Science Department and Pitzer College to Schmitz.