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Fast-Evolving Brains Helped Humans out of the Stone Age

People were once thought to have ancient psyches ill-suited to modern existence, but they have adapted much more quickly than early theories had predicted
cave paintings stone age mind evolutionary psychology



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Just like our animal skin–clad ancestors, we gather food with zeal, lust over the most capable mates, and have an aversion to scammers. And we do still wear plenty of animal skins. But does more separate us from our Stone Age forebears than cartoonists and popular psychologists might have us believe?

At first blush, parsing the modern human in terms of behaviors apparently hardwired into the brain over eons of evolution seems like a tidy, straightforward exercise. And 30 years ago, when the field of evolutionary psychology was gaining steam, some facile parallels between ancient and modern behaviors lodged themselves in the popular conceptions of human evolution. "It's very easy to slip into a very simplistic view of human nature," says Robert Kurzban, an associate professor of psychology at the University of Pennsylvania, citing the classic Flintstones stereotype.

Advances in neuroscience and genetics now suggest that the human brain has changed more rapidly—and in different ways—than was initially thought, according to a new paper published online July 19 in PLoS Biology.

"There's been a lot of recent evolution—far more than anyone envisioned in the 1980s when this idea came to prominence," says Kevin Laland, a professor at the University of Saint Andrew's School of Biology in Scotland and co-author of the new paper. He and his colleagues argue that today's better understanding of the pace of evolution, human adaptability and the way the mind works all suggest that, contrary to cartoon stereotypes, modern humans are not just primitive savages struggling to make psychological sense of an alien contemporary world.

Brain changes
A few decades ago, when researchers were laying the groundwork for the field of evolutionary psychology, the idea that evolution was primarily a gradual, almost geologically paced force "was a tenable view," Laland says. More recent studies, however, have found evidence of speedy evolutionary change in animals—as well as hundreds of changes in the human genome that appeared within tens of thousands, rather than over hundreds of thousands or even millions of years.

"It seems implausible that all of that change has been going on without changing how the brain works," Laland says. And if the brain has been changing over the millennia, along with the climate, culture and other environmental conditions, then there might be far less so-called "adaptive lag" than early evolutionary psychology researchers—and the broader public—had previously assumed.

Laland acknowledges that rapid evolution of the brain is not "inevitable by any stretch of the imagination." But he and his co-authors noted that relatively recent changes from "culturally facilitated changes in diet, to aspects of modern living that inadvertently promoted the spread of diseases" have left their mark on the human genome. And those changes have included "genes expressed in the human brain," they wrote.

Creating creature comforts
The inner sanctum of the suburban shopping mall might bear little resemblance to the African savanna on which our ancestors are thought to have evolved. But Laland notes that it is unlikely humans, imperfect though we might be, would consistently design environments to which we are ill suited.

A traditional, more passive take on evolutionary psychology "fails to recognize that humans are changing their environment," and not at all randomly or haphazardly, Laland says. "We've built environments that are well suited to our biology, so we don't find ourselves massively maladapted for the contemporary world."

As much as pop psychology has drawn from the notion that because of our tribal past on the savannas of Africa, we humans are best suited to live in small clusters spread thinly across vast spaces, an evolutionary view of population numbers refutes that notion. Although many other developments and technologies have come along to help us reproduce almost like rabbits, Laland argues that "if it were the case that humans were adapted to environments in the Pleistocene [epoch ending more than 10,000 years ago] but not the Holocene [modern era, which followed], you would expect human populations would have shrunk when they moved into urban environments."

Instead, the variety of environments in which humans seem to thrive highlights the "extraordinary level of adaptive plasticity afforded by our capacities for learning and culture," Laland and his co-authors noted in their paper.

To decipher these dizzying potentials, Laland and his colleagues advocate first taking a functional, neurological approach, tracking down activity in the brain via MRI scans and genetic studies. Figuring out how the brain does what it does on a more fine-grained scale will help, in turn, guide future research to track just how quickly and in what ways the Homo sapiens brain has changed since we regularly engaged in the cliched behavior of clubbing animals or communicating via grunts.

Adaptable brain science
Scientific views of the nature of the human mind may be changing rapidly in sync with better understanding of our capabilities. Early evolutionary psychologists have often favored something like a "jukebox" model of the brain, in which it contains any number of evolved, preprogrammed behaviors waiting to be set off by various stimuli, as if at the touch of a button. Laland and his colleagues instead argue for "a very different model of how the mind works," he says, in which the human mind is much more plastic, and perhaps more akin to a collection of musical instruments awaiting a jam session; the tune they will play depends more on developmental and cultural experiences than on engrained compositions. That flexibility may be what helped our ancestors cope with the world changing around them—and to participate in those changes by further remolding their environment to their own ends.

Not unlike the brain, the field of evolutionary psychology might have been evolving more quickly than many have realized. "The discipline has been perceived as simplifying," says Kurzban, who was not involved in the new paper. "Human nature is really complicated, and the brain is the most complicated thing we know of."

As an evolutionary and developmental psychologist who has also studied economics and anthropology, Kurzban says that he finds his field has already become quite multidisciplinary. "One of the things that evolutionary psychology illustrates is the importance and productivity of integrating information across disciplines," he says.

Laland hopes that an ever-widening spiral of scientists will help to create an even more robust understanding of how our behaviors came to be. Future research into developmental psychology, neuroscience and genetics might help to crack the code of what we have long taken for granted as "human nature." Already some researchers are using these disciplines to work out "the anatomy of what we used to call 'instincts,'" Laland says.

"It's still a young field," Kurzban says. And it might stay convoluted for quite some time. But like the brain itself, that might not be a bad thing. "As it grows there will be a larger surface area for collaborative work," he says.

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