What is the “New Thinking” about Human Cognitive Evolution?

In 2011, a conference convened to discuss what they labeled as the “New Thinking” (NT) about human cognitive evolution. The NT challenges many tenets of how evolutionary psychology has been pursued over the last twenty years. The journal Philosophical Transactions of the Royal Society B has recently published a special issue about the NT which challenges virtually all of the assumptions on which evolutionary psychologists have based their research for the last two decades and offers a drastically new way of approaching the evolution of human cognition that they claim is both more theoretically feasible and more empirically approachable. Most of this review is based on the introduction (like most of the articles in the issue, it’s behind a paywall) to the issue written by one of the editors of the issue, Cecilia Heyes of Oxford, who also contributed a review article to the issue.

Since the early 1990s, evolutionary psychology has become an influential yet controversial addition to the study of human cognitive evolution. The most popular brand of evolutionary psychology is that introduced by John Tooby and Leda Cosmides of the University of California, Santa Barbara, often referred to as the Santa Barbara School or simply as Evolutionary Psychology (EP), capitalized. EP developed out of earlier scientific movements like the sociobiology and human behavioral ecology which attempted to apply evolutionary concepts to subjects to which evolution had not traditionally been considered relevant, such as social behavior and family dynamics.

EP has been popular in the media. Reporters tend to enthusiastically report research findings from EP, most likely because the field has the impression of confronting directly the so-called nature vs. nurture dichotomy and allows for spectacular headlines about sex and violence. Psychologists and journalists have produced a number of high profile books about EP such as Steven Pinker’s How the Mind Works and The Blank Slate, Robert Wright’s The Moral Animal, and a persistent march of books about the evolutionary history of X (where X could be art, religion, politics, war, morality, &c., &c.).

EP is based on a few foundational principles. First, the mind is seen as being a set of adaptations to the ecological and social environment in which it was evolved. Second, that time period is generally identified as the Pleistocene, or from about 2.5 million years ago to about 12,000 years ago, coinciding with the end of the last ice age and the earliest development of agriculture. Before then, all humans had subsisted as foragers living in groups of about 20 to 50 people with smaller groups that splintered off during the day to hunt, fish, and gather resources. By studying the rapidly declining number of foraging groups still living that lifestyle today (though virtually none are unaffected by the modern world around them), anthropologists think that we have a fairly good idea of the types of small societies that ancestral hunter-gatherers formed and of the environments in which they lived. EP proposes that our minds are full of adaptations to that mode of life.

And third, EP assumes a model of the mind that makes specific predictions about how those adaptations are structured. Most evolutionary psychologists view the mind as massively modular, or as composed predominantly of small mechanisms that perform some small computational action on a certain kind of informational input for which it is intended (or domain specificity).

Modularity is a concept taken from computer science, and is an appealing way to think about cognition. If the brain’s actions are broken down into smaller components, then it becomes easier to understand how a mass of seemingly unorganized neurons can perform complex operations. Those small functions can also then potentially be studied independently.

Adaptations occur in a massively modular system by either tweaking an existing system to improve its function, by co-opting existing systems to perform a new function, or by evolving a new system. Importantly, however, such adaptations are thought to be brought about by genetic mutations.

EP has been controversial, however. Its critics often cite methodological issues that complicate how scientists can approach the history of human psychology, particularly because most of the phenomena that evolutionary psychologists tend to study (art, religion, politics, morality, language, &c., &c.) are not performed by other animals except in limited ways. With no comparative species available, it is often unclear if a behavior is the product of genetic inheritance or the product of learning. Evolutionary arguments for the origins of human behaviors are often taunted as being “just-so stories,” offering little more than untestable post-hoc stories of only how a phenomenon might have come into existence, often with no reliable way to distinguish it from its alternatives.

The NT challenges not the methodological concerns about EP, but rather those theoretical principles around which it is structured: adaptation to the Pleistocene, massive modularity, and the strong role of genetic inheritance. The NT stresses that the Pleistocene was an important phase in human evolution, but that there is a much longer history leading up to the Pleistocene that cannot be ignored. Such a myopic view of cognitive evolution ignores the long evolutionary past that created the structures which the Pleistocene humans inherited, and it ignores the constraints that that history places on what kind of adaptation is possible. The NT requires a much more comparative methodology (which is convenient since most of the authors of the articles are comparative psychologists).

The NT also challenges the idea that the brain is composed of innate domain-specific evolved modules. They argue instead that the brain is equipped with powerful domain-general mechanisms which, through experience during development, construct the sets of domain-specific mechanisms that are observed in the brain.

The most convincing evidence for this argument is the neuroscience of reading. Written language was only developed around six thousand years ago, and until relatively recently, essentially every human on earth was illiterate. No one would argue that the brain systems that support reading are products of natural selection; it is a novel function that our brains acquire. Reading shows all of the signs of being another domain-specific modular construction, the kind that would have been assumed to be genetically based if we didn’t already know that it wasn’t. There is even a part of the brain—a posterior patch of the left midfusiform gyrus—that reliably activates when it is presented with written letters and nothing else. Some researchers have named it the “visual word form area” (though others have challenged how specific it is). Nevertheless, reading activates a recurring network in the same way as other actions which are argued to have deep evolutionary roots.

EP does allow for some plasticity in brain function. Their account would be that the brain learns to read by reusing relevant brain structures which are already present—perceptual mechanisms like recognizing line arrangements and language mechanisms like mapping semantic meaning to stimuli—and building a new network that performs the new function. However, those original mechanisms are still thought to be evolved adaptations. The NT, on the other hand, argues that there are domain-general “cognitive-developmental mechanisms” that, through experience, build the cognitive mechanisms that are typically seen as evolved adaptations such as theory of mind and socio-cultural learning as well as learned abilities like reading.

The last challenge to EP is about how these mechanisms develop given a domain-general cognitive-developmental mechanism. Genetics are central for cognitive adaptation in EP. The NT proposes a much more rich and varied account of how adaptive cognitive functions can be constructed. Most importantly, they emphasize the importance co-evolution and cultural evolution.

They identify two different types of co-evolution: techno-social and gene-cultural evolution. Techno-social evolution occurs when selection pressures for two different abilities create a feedback loop that ends up developing each either beyond what would have been possible on its own or at a faster rate. The example that Heyes offers is a potential co-evolutionary link between tool making and cooperation. As tools increase in complexity, a new pressure is created to increase cooperation, since more people could be necessary to maintain a division of labor or to provide the necessary education to those learning the new technology. That increase in cooperation then might give extra value to new technological innovations. And that cycle could continue until there is some reason for it to decelerate. Heyes argues that this process might either provide benefits to both the techno-cognitive or socio-cognitive systems, or else a shared domain-general cognitive system that supports them both.

The second type of co-evolution is gene-cultural co-evolution. This occurs when a culturally evolved practice introduces a pressure on genetic evolution. The canonical example is the evolution of lactose tolerance in adults by many pastoralist groups. When livestock were domesticated, their milk became an abundant new exploitable resource. Most people stop producing lactase—the enzyme that breaks down the lactose protein—during early childhood. Pastoralists with a mutated version of the gene that ends lactase production, however, were able to keep drinking cattle milk, which can be a rich food source. Those who continued to produce lactase were then able to survive at higher rates and pass on more copies of that mutated gene until it became dominant within the population. Thus, a cultural trait—drinking the milk of domesticated cattle—created a pressure that affected genetic evolution.

The NT also places a greater emphasis on cultural evolution in cognitive and behavioral development. In his article in the special issue, Peter Godfrey-Smith of the City University of New York, specifies three levels at which cultural evolution occurs. At the lowest level, the micro level, culture evolves by a differential imitation of different cultural variants. If there are two different methods for thatching a roof in a society, then the different rates at which each method used is a form of cultural evolution, just as different rates of reproduction between two versions of a trait in a species is genetic evolution.

Humans are distinct—as far as we can tell—by our culture being cumulative, meaning that we innovate upon existing ideas to develop better ones, rather than invent new ideas each time. Cumulative culture, then, is cultural evolution at the meso level. The archaeological record shows the development of increasingly complex stone tools, each being improvements upon older styles of stone tools rather than entirely new inventions.

As cumulative culture carries on in different environments and in different groups, then cultural evolution occurs at the macro level. At this level, different cultures are created, or different collections of learned cultural ideas and behaviors that have been culturally evolved after a history of differential imitation and cumulative cultural development. This is what we might think of as the “phylogenetic level” (as Godfrey-Smith calls it) in that it is a process similar to speciation in genetic evolution. We might study cultural evolution at the macro level by tracing the history that led up to its present state, just as we might study the evolutionary history of the hand or vocal tract.

If cognitive development involves the domain-general cognitive-developmental mechanisms proposed by the NT, then cultural evolution can have a much deeper and more profound effect than possible in the EP framework.

The NT is still what it claims to be, the new thinking, and is thus not nearly well enough tested to be taken as the new paradigm in the study of human cognitive evolution. However, the evidence provided in the special issue is promising. Science advances by taking whats good about the old, and throwing the rest off to accumulate more of the good—one of the best examples of cultural evolution at work. If the ideas pan out, then we may have an entirely different framework, one much more complex and dynamic, to frame our study of how the human mind came to be the powerful device that it is.

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6 comments

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