Specimens at the California Academy of Sciences
Not a land-dwelling fish, by the way. Just a cool picture.

Ed Yong in The Atlantic writes about new research on the relationship between the evolution of vision and the movement of fish from water to land. Scientists have long known that some species of fish started hanging out near the shore, then venturing on land, and eventually living on land full-time, starting about 385 million years ago. During this process, Yong writes, “their flattened fins gradually transformed into sturdy legs, ending in feet and digits. Rather than paddling through water, they started striding over solid ground.”

Naturally the evolution of legs has gotten lots of attention among paleontologists, but in a new article, a team led by Northwestern University professor Malcolm MacIver argues that changes in vision played a very significant role in the transition, too.

It turns out that the first tetrapods (fish who moved onto land) had much larger eyes than other fish– and those eyes had gotten a lot bigger before they became permanent land-dwelling creatures. For the previous several million years the eyes grew larger, and moved from the sides of the head to the top, like crocodiles.

The change in vision was connected to an increasing interest in goings-on on land, and particularly the search for terrestrial edibles. The biggest evidence for this is that bigger eyes actually didn’t provide much of an advantage in water:

By simulating the kinds of shallow freshwater environments where their fossil species lived—day to night, clear to murky—they showed that bigger eyes make precious little difference underwater. But once those animals started peeking out above the waterline, everything changed. In the air, a bigger eye can see 10 times further than it could underwater, and scan an area that’s 5 million times bigger.

In the air, it’s also easier for a big eye to pay for itself. A predator with short-range vision has to constantly move about to search the zone immediately in front of its face. But bigger-eyes species could spot prey at a distance, and recoup the energy they would otherwise have spent on foraging. “Long-range vision gives you a free lunch,” says MacIver. “You can just look around, instead of moving to inspect somewhere else.”

So basically the tetrapods evolved to spot food on land, then eventually relocated permanently to be closer to their food sources. As Yong writes, “eventually, their limbs changed too, allowing them to make longer forays into this new world—a world of not only solid ground, but also large distances.”

Tiger at the Museum of Natural History
Vision and legs = hunting ability

Years ago I read Andrew Parker’s In the Blink of an Eye, about the evolution of vision and the Cambrian explosion. I was very impressed with his argument that the acquisition of sight was one of the factors that drove the development of new species in that period, the growth of coloration and camouflage, etc. So perhaps I’m more likely to believe in the “vision drives evolution” story.

This way to the Visions of the Future Conference

Finally, there’s this:

In a way, bigger eyes let you see further into time as well as space. Now, there are more benefits to abilities like planning, strategic thinking, and complex decision-making. Animals become less reactive, and more proactive…. “Maybe having this expanded sensing volume allowed us to break the knee-jerk connection between sensing and moving, and decouple thoughts from action,” he [MacIver] speculates. “Now you’re choosing the best thought for your environment, which looks like a kind of proto-consciousness.”

Futures is full of vision metaphors: we talk all the time about scanning the horizon, seeing the unexpected, etc. This suggests that the connection between vision, thinking about the future, and action is more robust than we think.