Prehistoric ‘clutter’ on land led to bigger, smarter human brains

The ways our ancestors adapted to live in patchy landscapes cluttered with obstacles “poured jet fuel” on the evolution of the brains of animals and early human ancestors, according to researchers at Northwestern University.

The combination of our enhanced eyesight and higher intelligence to survive in this complex land environment is “why we can go out for seafood, but seafood can’t go out for us,” said Malcolm MacIver, a professor of biomedical and mechanical engineering in Northwestern University’s McCormick School of Engineering.

Maciver and his colleagues use computer simulations to study aspects of evolution. Previously, they determined that 380 million years ago, just before animals moved out of the sea to live on land, their eyes tripled in size, he told CNN.

In water, this increase in eyesight capability doesn’t offer much of an advantage. Instead, survival in open water is a speed game where prey have to outswim their predators.

Their research suggested, however, that these animals were more like crocodiles in that they lived in the water, but let their eyes rise above the surface, “enabling them to see hundreds of times further than is possible in water because water rapidly absorbs and scatters light,” said Maciver, who is also a professor of neurobiology in the Weinberg College of Arts and Sciences at Northwestern.

These animals likely hunted insects that lived on land, lurching out of the water to snack on them. Over time, they evolved to move more on land, and their increased eyesight provided key information about their surroundings.

MacIver and his colleagues were curious. “How could seeing things so much further away modify how we try to get the things we need to live, like food and mates, while avoiding things like predators?”

Simulating ancient life

In their newest simulation, published this week in the journal Nature Communications, the researchers used existing computational models showing how animals interacted with their landscapes. They adapted these models to show whether life on land favored planning or habit-based action.

“We ask the question: how hard does the prey need to think to survive, as we vary the complexity of the environment?” MacIver said.

The model is essentially a 15 by 15 checkerboard with both open and closed squares. The closed squares represent obstacles. Prey has to navigate through these squares to reach a goal. Meanwhile, a predator is moving through this landscape after the prey.

Their simulations showed that in a patchy landscape, a mix of grasslands with trees, bushes, boulders and knolls, the ability to survive was greatly enhanced by planning, which MacIver said is “a distinct brain capacity that seems to have evolved in mammals and birds, and seems particularly well developed in our own species.”

There was no advantage to strategic thinking or planning in a totally open or totally closed environment, like open water or a dense jungle.

But in a patchy landscape, each move could either help hide or reveal the prey’s position to a predator. So it requires contemplating several possible ways of navigating the space.

“You need quite some brain power to work through those tactics,” MacIver said. “Seeing farther away affords you the time and space to ‘think further away’ as well.”

In the case of ancient humans who stood upright on two feet as opposed to their chimpanzee relatives on all fours, they could survey the patchy landscape as a predator and also have to think like prey to avoid anything that was after them, like saber-toothed cats.

“Incidentally, our brains nearly quadrupled in size after we split off from our nearest primate ancestors, the chimpanzees,” MacIver said. “This brain size increase could be related to how much brain power it takes to be strategic in these spaces, but it will take more research to know for sure.”

MacIver and his colleagues turned their simulation into an online game, navigating through different landscapes as prey to see if you can reach your goal before a predator catches you.

Life in water vs. life on land

It’s difficult to imagine what life may have been like had it remained strictly in water, but MacIver was willing to speculate.

“There would be no theory of special relativity. There would be no SpaceX. There would be no such thing as a 747,” MacIver said.

“Although these things are all about humans and their ingenuity, the cognitive power that drives them have neural bases that we can see in other animals that live on land, such as mammals and birds.”

The distribution of cognitive power is entirely uneven between animals living on land versus those living underwater, MacIver said.

Dolphins and whales are the exception because they actually evolved on land and returned to the water. Other exceptions include octopus and cuttlefish, which were subject to predation by land animals as well as dolphins and whales; they could have evolved to evade them.

Next, MacIver and his colleagues want to observe how real animals behave in the lab, as well as using robotic predators and prey.

“My biggest hope is that through work like this, scientists will eventually have a clear enough understanding of how we go about planning to know how to manipulate this ability in our own brains, perhaps by way of some kind of cognitive prosthetic, MacIver said.

“With that, perhaps we can make planning for distant threats or opportunities less difficult than we currently find it to be as a species.”