How Did General Intelligence Evolve?

If the contents of the human brain are domain-specific, as evolutionary psychologists contend, how can evolutionary psychology explain general intelligence, which is seemingly domain-general?

General intelligence refers to the ability to reason deductively or inductively, think abstractly, use analogies, synthesize information, and apply it to new domains. It is a measure of how (and how well) you think, not of what you know, although what you know is influenced by your intelligence.

The concept of general intelligence poses a problem for evolutionary psychology. Evolutionary psychologists contend that the human brain consists of domain-specific evolved psychological mechanisms, which evolved to solve specific adaptive problems (problems of survival and reproduction) in specific domains. So, for example, we have the cheater detection mechanism for the domain of social exchange, and the language acquisition device for the domain of native language acquisition. Evolved psychological mechanisms work only in their designated domain. You cannot use the cheater detection mechanism to learn your native language or use the language acquisition device to detect who may be violating an implicit social contract. But if the contents of the human brain are domain-specific, how can evolutionary psychology explain general intelligence, which appears to be domain-general, applicable to and useful in many domains?

I believe that what is now known as general intelligence may have originally evolved as a domain-specific adaptation to deal with evolutionarily novel, nonrecurrent problems. The human brain consists of a large number of domain-specific evolved psychological mechanisms to solve recurrent adaptive problems, such as problems of food procurement and mate selection. In this sense, our ancestors did not really have to think in order to solve such recurrent problems. Evolution has already done all the thinking, so to speak, and equipped the human brain with the appropriate psychological mechanisms, which produce in us the appropriate preferences, desired, cognitions, and emotions, and motivate adaptive behavior in the context of the ancestral environment.

All our ancestors had to do to solve their everyday adaptive problems was to follow the dictates of such evolved psychological mechanisms and behave according to how they felt, following their emotions and feelings. Conscious and deliberate reasoning was seldom necessary for our ancestors because most of their adaptive problems were recurrent and familiar, and they had innate solutions in their brains.

Even in the extreme continuity and constancy of the ancestral environment, however, there were likely occasional problems that were evolutionarily novel and nonrecurrent, which required our ancestors to think and reason in order to solve. Such evolutionarily novel problems may have included, for example:

1. Lightning has struck a tree near the camp and set it on fire. The fire is now spreading to the dry underbrush. What should I do? How could I stop the spread of the fire? How could I and my family escape it? (Since lightning never strikes the same place twice, this is guaranteed to be a nonrecurrent problem.)

2. We are in the middle of the severest drought in a hundred years. Nuts and berries at our normal places of gathering, which are usually plentiful, are not growing at all, and animals are scarce as well. We are running out of food because none of our normal sources of food are working. What else can we eat? What else is safe to eat? How else can we procure food?

3. A flash flood has caused the river to swell to several times its normal width, and I am trapped on one side of it while my entire band is on the other side. It is imperative that I rejoin them soon. How could I cross the river? Should I walk across it? Or should I construct some sort of buoyant vehicle to use to get across it? If so, what kind of material should I use? Wood? Stones?

To the extent that these evolutionarily novel, nonrecurrent problems happened frequently enough in the ancestral environment (a different problem each time) and had serious enough consequences for survival and reproduction, then any genetic mutation that allowed its carriers to think and reason would have been selected for, and what we now call “general intelligence” could have evolved as a domain-specific adaptation for the domain of evolutionarily novel, nonrecurrent problems. Because such problems were not recurrent features of the ancestral environment, there are no innate solutions provided by existing psychological adaptations.

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From this perspective, general intelligence may not have been very important – no more important than any other domain-specific psychological adaptation – in its evolutionary origin but it became universally important in modern life, only because our current environment is almost entirely evolutionarily novel. The new theory suggests, and empirical data confirm, that more intelligent individuals are better than less intelligent individuals at solving problems only if they are evolutionarily novel. More intelligent individuals are not better than less intelligent individuals at solving evolutionarily familiar problems, such as those in the domains of mating, parenting, interpersonal relationships, and wayfinding (finding your way home in a forest), unless the solution involves evolutionarily novel entities. For example, more intelligent individuals are no better than less intelligent individuals at finding and keeping mates, but they may be better at using computer dating devices. More intelligent individuals are no better at finding their way home in a forest, but they may be better at using a map or a satellite navigation device.

I believe scientists and civilians alike may have grossly exaggerated the importance of general intelligence in everyday life. Intelligence does not help you with really important problems in your life, such as maintaining a successful relationship, being a good friend, and raising children. It merely helps you with solving unimportant, evolutionarily novel problems like getting formal education, making money in a capitalist economy, and flying an airplane.