Steven Pinker, in a recent paper in the Proceedings of the National Academy of Sciences, proposes an explanation of how human intelligence evolved. He begins by noting that Charles Darwin had no problem believing that intelligence could be explained by evolutionary theory. However, Alfred Russel Wallace, who arrived at the idea of natural selection around the same time as Darwin, thought that because abstract reasoning would have been of no use to prehistoric humans, intelligence must have been the work of a superior being rather than solely the result of natural processes. Scientists have sided with Darwin, but Wallace’s point about the dubious adaptive value of higher cognitive functions to earlier humans is worth examining. Pinker offers an explanation of how we gained our unique profile of cognitive capabilities.
The explanation rests on two things: the idea that we evolved to fit a cognitive niche, and our capacity for metaphorical abstraction. The concept of a cognitive niche originated with John Tooby and Irven DeVore; the basic idea is that we brought to the evolutionary arms race the rudiments of several characteristics that allowed us to exploit other organisms by reasoning and information-sharing rather than by sheerly physical or chemical means (running faster, producing toxins as plants do, etc.). Once we began to move into this niche, new possibilities opened up, and a host of peculiarly human traits likely co-evolved. Pinker emphasizes three traits: the smarts needed to develop and use tools, the capacity for cooperation with those to whom we are not related, and the capacity for the uniquely human combinatorial system of grammatical language.
He discusses briefly how various quirks of the human organism (for example, our relatively long childhoods and long lives, our cultural differences) could have arisen as a result of the development of these capabilities, and also some of the factors that might have predisposed us toward moving into the cognitive niche (prehensile hands, the inclusion of meat in the diet, living in groups).
This is interesting for several reasons. For one, it’s intuitively appealing (to me, at least) to think of a multitude of interwoven causes for something as complex as human intelligence rather than a single development on which everything else hinged. Also, this theory might explain very nicely why we seem to share some capabilities with other animals, things that were once thought to be uniquely human (compassion for conspecifics, tool use, etc.), but we are the only ones to have such well-developed versions of them and to have them all in combination. Pinker also mentions that we test and fine-tune our strategies on the fly within our own lifetimes rather than relying on the much slower pace of evolutionary change to develop responses to environmental challenges or changes in the organisms we eat or otherwise exploit:
Because humans develop offenses in real time that other organ-
isms can defend themselves against only in evolutionary time,
humans have a tremendous advantage in evolutionary arms races.
This seems to explain why we are uniquely destructive as well, and it gives us (although we should already know this) an extraordinary responsibility.
I was also struck by the following:
The selection pressures that the theory invokes are straight-
forward and do not depend on some highly specific behavior (e.g.,
using projectile weapons, keeping track of wandering children) or
environment (e.g., a particular change in climate), none of which
were likely to be in place over the millions of years in which modern
humans evolved their large brains and complex tools. Instead it
invokes the intrinsic advantages of know-how, cooperation, and
communication that we recognize uncontroversially in the con-
temporary world.
This seems to sidestep my objections to the way evolutionary psychologists sometimes seek to explain our behavior and the way they assume there was a single environment that definitively shaped everything about us.
You still have to wonder how we developed the ability to understand and use things that our ancestors had no pressing need for (differential equations, the concept of the state). That’s where the idea of metaphorical abstraction comes in. Basically, this means that we are able to take relationships that apply to space and force and then abstract them out to apply to other things. Our language is full of such metaphorical uses; when the Dow goes up, it doesn’t really ascend skyward, for example (although when it falls we do sometimes seem to hear a certain sickening thud). These metaphors reveal that we have pressed various physical concepts into use in novel ways. The power of this is that it allows us to mentally combine and manipulate abstractions. He gives lots of interesting references to the literature on this capability.
The article also offers some insight into how the theory of the cognitive niche could be tested, which I find exciting:
The theory can be tested more rigorously, moreover, using the family of relatively new techniques that detect “footprints of selection” in the human genome (by, for example, comparing rates of nonsynonymous and synonymous base pair substitutions or the amounts of variation in a gene within and across species). The theory predicts that there are many genes that were selected in the lineage leading to modern humans whose effects are concentrated in intelligence, language, or sociality. Working backward, it predicts that any genes discovered in modern humans to have
disproportionate effects in intelligence, language, or sociality (that is, that do not merely affect overall growth or health) will be found to have been a target of selection. This would differentiate the theory from those that invoke a single macromutation, or genetic changes that affected only global properties of the brain like overall size, or those that attribute all of the complexity and differentiation of
human social, cognitive, or linguistic behavior to cultural evolution.
However, Jerry Coyne, in his blog Why Evolution is True discusses this paper and goes into some very interesting details on why such testing would be difficult.
In short, Pinker’s paper is full of meaty food for thought and discussion, and it also offers a way to look for evidence, problematic though that may be. Fascinating stuff! The full citation is:
Steven Pinker, The cognitive niche: Coevolution of intelligence, sociality, and language. Proceedings of the National Academy of Sciences, May 11, 2010; 107 (Supplement 2): 8993–8999. DOI: 10.1073/pnas.0914630107
