In the Scottish National Gallery of Modern Art, there is a work that is no more than a list of names: anyone who can remember the artist, Douglas Gordon, meeting him in his lifetime. The frame flows on in endless columns, down a corridor and over walls several stories high. It’s dizzying, but far from complete, considering Gordon is only 52 years old.
The frame is an abstract idea about people, made concrete in black paint: we are an intensely, bewilderingly social species. Our brains somehow have a huge vault for storing details about other people, even if those details are little more than facial or name recognition.
It’s possible that this huge vault, along with a myriad of other cognitive abilities of our brains, is there precisely because of the intense sociality of our species. One of the most prominent explanations for cerebrum evolution is that large social groups lead to problem-solving challenges, which in turn create evolutionary pressures for smart cerebrums capable of navigating social situations.
Proponents of the social brain hypothesis point to piles of evidence to support it, but a series of recent publications raise questions about whether it should dominate thinking in its field. It’s true that in primates, large brains generally coexist with large social groups, but that correlation has started to look shaky when researchers poke at it.
Definitive answers are hard to come by because when it comes to primate brains and behavior, what we don’t know narrows down to what we’re doing. The precise combination of factors that caused evolutionary changes has been lost to history. That has left the field struggling to test this hypothesis with data that is far less complete than it would like — a challenge shared with many other fields of science.
But even in this gray zone, progress can be made — a gradual dilution of darkness as researchers focus on answering one small question at a time. Even when the most much-needed information is out of reach, science as a whole can move forward.
How do you solve a problem like cognition?
Big brains may not seem like such a big mystery. You have a bigger brain, you are smarter, you take care of your survival needs more easily and you can start to spend time painting beautiful antelopes on cave walls. Boom, solved, it’s only a matter of millennia before we get to the moon.
The mystery lies in the fact that big brains are hungry. They are the organ equivalent of a muscle car engine, guzzling obscene amounts of fuel, while for many animals a Prius seems to do just fine. To justify its existence, the intellectual horsepower produced by the larger brain would be better worth its weight in calories. And it’s not just humans who have big brains: All of our primate relatives seem to be on the smart side, including our closer ape cousins, such as chimpanzees and gorillas. More distant relatives such as monkeys and lemurs are also quite intelligent.
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Primates generally have brains that are insanely large enough to demand an explanation — what makes it worth it in a lemur’s world to drive around a low-calorie black hole?
Larger social groups make it worthwhile, according to the social brain hypothesis. Large groups are thought to have evolutionary advantages, such as protection from predators. But living in close social relationships with other individuals presents a host of cognitive challenges. Those animals that can handle the cognitive challenges survive and thrive; across generations, that means a species with bigger brains.
And that’s what the evidence points to: Primates with larger social groups also have larger brains. As the evidence has grown, the idea has become well established among scientists in the field. Similar results have been found in other mammalian families, such as ungulates (deer, camels, and the like) and cetaceans (whales and dolphins). Researchers have reported that individual magpies who are more sociable are also better at solving puzzles. “It’s definitely been the consensus,” Rob Barton, a researcher who studies brain evolution, said in a phone call with Ars.
Review the data
Barton has long been a proponent of the social brain, even co-authoring work on the hypothesis with its main proponent, Robin Dunbar. But he was concerned about problems with the data and wanted to take another look. “It occurred to me that this hadn’t really been fully done since before,” he explained. He started with a cursory glance, and when the results were unexpected, he passed the project on to a doctoral student, Lauren Powell, to delve deeper into the work.
“I honestly had no agenda on this,” Barton told Ars. “I expected to find a correlation with social group size.” But that’s not what they found. Instead, they found that brain size was more closely related to factors in a primate species’ environment, such as how big their territories were and what kind of food they ate. Unsurprisingly, higher-calorie diets went hand in hand with bigger brains.
Meanwhile, another group of researchers, led by primatologist Alex DeCasien, published a paper with a similar finding: Fruit-eating primates had larger brains than leaf-eating primates. This pattern matched the brain size data better than the primates’ social lives.
Should we switch from the social brain hypothesis to the ecological brain? Not so fast. Powell, Barton and their colleague Karin Isler compared different data sets and found that the results looked different depending on how they split the data.
Small, noisy data sets make a clear answer impossible. But all the datasets currently available to the field are, well, small and noisy — the data the researchers would love to get their hands on is still way out of reach.
Dream the impossible data dream
Researcher Susanne Shultz, a proponent of the social brain hypothesis, was impressed by Powell’s analysis. “It is very good. They have tested things thoroughly and their conclusions are very justified,” she said in a telephone conversation with Ars. But, she emphasizes, there should be two different correlations in the conversation: there is the correlation between group size and brain size and a correlation between group size and a brain region called the neocortex.
The neocortex receives and integrates information from the outside world, organizes it and works together with other brain regions to convert that information into behavior. In large-brained animals, such as primates, the neocortex makes up a disproportionate portion of the total brain. Scientists are constantly improving their understanding of the neocortex, including figuring out how it communicates with other areas, but “the idea still sticks that the neocortex is the ‘intelligent’ part of the brain,” Barton says.
Powell and her colleagues looked at the whole brain and found no support for the social brain hypothesis. The jury is still out on the neocortex correlation, but Barton points out that the neocortex is such a large part of the total brain that if the neocortex correlates with some other factor (such as social group size), we would expect that total brain size correlates , te. So if we don’t find the correlation for total brain size, it seems less likely that the correlation would be there for the neocortex.
To get the verdict, autopsies are required – many of them. And opportunities for primate autopsies are, unsurprisingly, not an everyday occurrence. “We can’t all start dissecting the brains of every animal we work with,” Shultz said.
It’s hard to pin down exactly how many primate species there are, but it’s safe to say there are currently over 200; the dataset of decent brain regions, published by Heinz Stephan and his colleagues in 1981, only includes about 40 species. Those are the data that support the neocortex findings.
Barton is actually a cheerleader for the idea that looking at specific brain regions is a better idea than looking at the brain as if it were a large lump – he points to nocturnal animals with enlarged olfactory areas associated with smell and diurnal species that have greater visual cortex. If you just looked at the whole brain of those groups, you wouldn’t get the full picture of how it is specialized. But because of the limited primate data, Powell, Isler, and Barton were able to get full-brain data on 114 species, so that’s what they used.
When they limited their analysis to just the species used in the Stephan dataset, the social brain seemed to be back in the running. The problem is, the dataset is skewed in some very important ways — it focuses more on African and Asian “Old World” monkeys, Shultz says, and less on America’s “New World” monkeys. Among those Old World species, the emphasis is heavily on the fruit eaters. Powell also points to a lack of good data on great apes, such as gorillas and orangutans, in the dataset.
It is possible for the neocortex correlation to show up because the skew in the data is coughing up a false positive. It is also possible that it is real. If a primatologist ever won the lottery and funded the dream data set, we’d find out.