Why are we humans so smart?

Philosophers like to pose “big” questions, ones that tickle the mind, make us think and make sure that when we do think we do it honestly. In the philosophy of science, an area I have more than a passing interest in, they also have great fun probing issues that scientists are pursuing. The best of these have been ones like “How did life begin?” or “How do brains ‘make’ consciousness?” or “What was there before the Big Bang?”

Note, these questions are ones that, in principle, have answers. I’m not including what others might call biggies like “Is God real?” or “Is there an afterlife?” Those are questions for theologians to ponder. Unlike the others, there are no verifiable answers to be had.

Throughout my fifty or so years as a cognitive scientist with an interest in the philosophy of mind, I’ve been intrigued by the one about consciousness. I think I’ve got a novel answer to it which I’ll get to some other day. Here, I’d like to ask that “biggie” that’s in the title and ask it in a way that makes it easy to talk about:

“Why are we so much smarter than we need to be?”

I think that’s a good way to phrase it. We evolved as a cognitively sophisticated species capable of thriving as hunter-gatherers living in relatively small groups for mutual aid, security and companionship. We hung around in this state for tens of thousands of years. In fact, in some isolated and remote regions, particularly in the Amazon, we still live in much this manner. Clearly, we’re smart enough to operate in this kind of ecological niche and do it with success.

But if a child born into one of these isolated tribes were, shortly after birth, relocated to Paris or Tokyo or Boston and grew up in a complex modern society they would be just fine. He or she would grow up to be a lawyer or a bank teller, maybe a cab driver or a philosopher because they are us and we are them. Whatever smarts we needed to function in these environments were housed in the same neuro-cognitive core we have today. When they evolved they allowed us to hunt cooperatively, develop complex kinship systems, acquire language, a sense of humor, rituals and religions. How is it that these rather mundane functions held within them the reserve capacity to develop string theory, program computers or ask questions like the one I’m asking here which requires nested representations (brains asking questions about brains)?

This disconnect is astonishingly difficult to explain. What is it about the human brain that it houses such remarkable residual cognitive capacity? What’s the point, from an evolutionary point of view, of having an organ that has this potential when it wasn’t “needed” for thousands of years? No other species has anything approaching this gulf between what is done compared with what can be done. Even the cleverest like bonobos, cetaceans or corvids have a terrible time trying to elevate cognitive functions beyond the upper bounds imposed by evolution. Corvids can be taught to solve some puzzles and chimpanzees can learn to deal with numbers, maybe as high as 9. Cetaceans may still have some of our kind of cognitive reserve but it’s awfully hard to do the research to find out and living in water without fingers is going to impose restrictions.

And there’s another wrinkle here. Being smart isn’t cheap. There are lots of tricky elements involved in calculating how much energy our brains use but the general consensus is that it’s around 15 to 20 percent of the body’s total expenditures – a lot for an organ that makes up only 1 to 3 percent of total body mass.

One possibility is that the energy needed for “serious thinking” isn’t that much compared with the brain’s total needs. Estimates vary but a common finding is that when engaged in careful thought, problem solving or complex executive functions the structures involved are only using some 1 or 2 percent of total metabolic expenditures. It could be, I guess, that whatever fluky mutations produced our extraordinary cognitive reserve weren’t very costly in any Darwinian way. So they just hung around in case we had a little leisure time one day and wanted to try working out symbolic logic or figuring out how to move the world with a fulcrum and a place to stand.

Another possibility is that there are common cognitive components to things that seem so sophisticated like solving some of the arcane mathematics of quantum mechanics and ordinary processes like those that give rise to a sense of humor. This, if true, would make our opportunistic, analytic brain a classic Gould-Lewontin “spandrel,” a system whose non-essential but ultimately wonderfully adaptive functions piggybacked on other critical forms.

Who knows? Not me. That’s the conundrum du jour.