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Hunting in savanna-like landscapes may have helped create planning circuits in the brain. Abundant obstacles and occlusions, terrestrial environments gave prey room to hide and predators cover for sneak attacks.

There is a pivotal scene in the 2012 movie The Hobbit: An Unexpected Journey when Gandalf, Bilbo Baggins and a party of dwarves are chased by orcs through a classic New Zealand landscape. For neuroscientist and engineer Malcolm MacIver of Northwestern University, the scene is a prime example of the kind of patchy landscape – dotted with trees, shrubs, boxers and rolling hills – that may have shaped the evolution of higher intelligence in humans, compared to their aquatic ancestors. . In particular, it falls within a “Goldilocks zone” — not too sparse and not too dense — that promotes strategic thinking and forward planning, leading to the development of “planning” circuits in the human brain, according to MacIver’s most recent paper. , published in Nature Communications.

This latest article builds on previous research. In 2017, MacIver and several colleagues published a paper in which they put forward an unusual hypothesis: Those ancient creatures that first crawled out of the water onto land may have done so because they found there was an “informative advantage” by looking through the air, as opposed to watering. Eyes can see much further into the sky, and that greater visual range could lead them to food sources near the coast. MacIver and his lead co-author, paleontologist Lars Schmitz of the Claremont Colleges, argued that this, in turn, drove the evolutionary selection of vestigial limbs, allowing the first animals to move from water to land.

That hypothesis arose from his research on South America’s black ghost knifefish, a nocturnal hunter that generates electrical currents in the water to sense its surroundings. After building a robotic version of the knifefish, with its own electrosensory system, he found that the volume of space in which it could detect prey (water fleas in this case) was about the same as for a fish that relies on vision to hunt water fleas. . The critical factor turned out to be that water absorbs and scatters light, limiting the distance that light can travel: typically 10 centimeters to 2 meters, compared to the 25 to 100 kilometers that light can travel in the air.

Our Myopic Inner Fish: Vision Helps Explain Why Our Fish Ancestors Came Ashore.

Increasing eye size would have the effect of turning on high beams in foggy conditions so creatures can see further, but eyes also require a lot of energy to maintain, making such development evolutionarily costly for ancient aquatic animals. But bigger eyes would provide a huge evolutionary advantage in the air, making the cost an acceptable trade-off in a terrestrial environment, MacIver reasoned.

So MacIver and Schmitz scanned the fossil record for evidence of an increase in eye size during the critical transition from water to land. They found that for about 12 million years, there had been a threefold increase in eye size during that transition period, from 13 millimeters before to 36 millimeters after. Even more intriguingly, that increase started before the full transition from water to land was complete. This suggested that those aquatic creatures that learned to raise their eyes, like a crocodile, to find new food sources on the nearby coast had encountered “the gateway drug to terrestry,” MacIver told Quanta Magazine in 2017.

The Goldilocks Zone

Now MacIver is back with an even more provocative hypothesis: The geometry of particular habitats determines evolutionary selection pressure in predator-prey contexts. “The basic idea is that open spaces — open grasslands, flat plains — are just speed games, favoring the predator, because they’re bigger,” MacIver told Ars. “Closed spaces – dense forests or jungles – prefer simple strategies for taking cover. Using a complexity measure, we show that both habitats have low complexity.” That measure of complexity is lacunarity, a geometric term to describe how patterns fill the space.

The sweet spot of complexity, according to MacIver, is a landscape like that in the hobbit chase scene, or like Botswana’a Okavango Delta, both of which have open grassland and mossy zones dotted with clumps of trees and similar foliage. “In this zone, neither speed games nor running for cover maximizes survivability,” MacIver said. “But planning—by which I mean thinking up future paths and choosing the best one based on what you think your opponent will do—gives you a significant advantage.” And that planning requires the kind of sophisticated neural circuitry typical of the human brain.

MacIver and his Northwestern colleague and co-author, Ugurcan Mugan, ran numerous supercomputer simulations, which showed that while looking further (MacIver’s original theory) is necessary for advance planning to evolve evolutionarily, this alone is not enough. Rather, it requires a combination of long-range vision and complex landscapes. This, in turn, may have led to the development of one of the most difficult cognitive operations: visualizing the future.

MacIver and his team then built new predator/prey simulations to test prey survivability under two different strategies. The first was habit-based, similar to entering a remembered password when prompted; the second was plan-based and included the ability to imagine different scenarios and select the one with the best chance of survival. They used a simple landscape with no visual barriers to simulate a water environment and added different objects, with different density distributions, to simulate land.

The results: In the simple water and land simulations, the prey showed low survival rates regardless of which strategy it used, demonstrating that there was no evolutionary advantage to being able to plan in environments that are very open or too densely packed. In the first case, the best bet is to try to outrun the predator; in the latter case, there are too few clearly available paths, and the densely packed environment hinders how far the prey can see.

But a patchy landscape in the Goldilocks zone of complexity showed a huge increase in survival rates for prey dependent on planning strategy, compared to the habit-based approach. The team at MacIver has developed an online game to illustrate how different landscapes (coral reef, jungle, savanna and open water) affect our ability to plan and evade a predator. (You can play it here.)

Screenshot from MacIver's online game showing how different landscapes affect the ability to plan and evade a predator.
enlarge Screenshot from MacIver’s online game showing how different landscapes affect the ability to plan and evade a predator.

YouTube/Northwest

Now MacIver sees evidence of the Goldilocks zone everywhere, including movies like the hobbit† “Using Space” [in the chase scene] was just fascinating in terms of this interplay between opaque and open spaces,” MacIver said. While he hasn’t figured out how to measure the exact landscape gap in that range, his conjecture is that it’s very close to his Goldilocks zone.

It was probably not a conscious choice on the part of the filmmakers; MacIver sees it as an intuitive understanding of what makes for an exciting chase scene. “It’s about anticipating something so powerful,” he said. “Seeing a scene unfold from a distance and anticipating something bad, or good, is about to happen is what drives the drama.” A dense rainforest or similarly messy landscape would obscure the action, while a flat, arid plane would be too predictable. But the scenery seen in the film (and in the savanna) is spot on. In those circumstances, “any move basically becomes like a chess move,” MacIver said — and so much more fun to watch.

Not bulletproof yet

MacIver is the first to admit that more work is needed to make his hypothesis “completely bulletproof,” especially regarding the nearly fourfold increase in brain size that occurred in humanoids after they diverged from chimpanzees. But his simulations “send a strong signal as to why terrestrial animals became ‘smart’ and aquatic animals did not,” he said. (A possible exception is cephalopods, which show signs of higher intelligence, perhaps because they were attacked by land animals, according to MacIver.)

He is currently working with Northwestern’s Dan Dombeck on a follow-up study, testing his computational predictions through experiments in robotic environments. “We’ve created this complex space with repositionable obstacles and controllable entropy, where there are two robots,” MacIver said. “One is a predatory robot powered by the same super-simple algorithm given in our paper. For example, when it sees the prey, it runs towards it. The other robot is the prey.” The prey must reach the target because the predator is in pursuit, just like in the online game.

More speculatively, MacIver thinks this may be relevant to why people struggle so much to ponder impending existential threats, particularly those in the distant future — climate change, for example, or antibiotic-resistant bacteria (or a global pandemic). “To the extent that you believe that the ability to think about the future was driven by a need to plan, and that our ability to think about the past is a derivative of this need, a lot of who we are depends on why we developed the circuits in the first place,” he said. “The reason we’re so bad at planning for the distant future could lead to limitations in this circuit that we haven’t yet developed the cultural technology to get around.”

DOI: Nature Communications, 2020. 10.1038/s41467-020-16102-1 (About DOIs).

Listing image by YouTube/Northwestern University

By akfire1

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