The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

A FISH KNOWS HOW TO SWIM THE INSTANT IT HATCHES, AND OFF it darts to fend for itself. When a duckling hatches, it can follow its mother over land and across the water within moments. Foals, still dripping with amniotic fluid, spend a few minutes bucking around to get the feel of their legs, then join the herd. Not so with humans. We come out limp and squalling and utterly dependent on round-the-clock care and supervision. We mature glacially, and do not approach anything resembling adult competence for many, many years. Obviously we must gain some very large advantage from this costly, not to mention risky up-front investment, and we do: It’s called culture.

In this chapter I explore how a specific class of brain cells, called mirror neurons, may have played a pivotal role in our becoming the one and only species that veritably lives and breathes culture. Culture consists of massive collections of complex skills and knowledge which are transferred from person to person through two core mediums, language and imitation. We would be nothing without our savant-like ability to imitate others. Accurate imitation, in turn, may depend on the uniquely human ability to “adopt another’s point of view”—both visually and metaphorically—and may have required a more sophisticated deployment of these neurons compared with how they are organized in the brains of monkeys. The ability to see the world from another person’s vantage point is also essential for constructing a mental model of another person’s complex thoughts and intentions in order to predict and manipulate his behavior. (“Sam thinks I don’t realize that Martha hurt him.”) This capacity, called theory of mind, is unique to humans. Finally, certain aspects of language itself—that vital medium of cultural transmission—was probably built at least partly on our facility for imitation.

Darwin’s theory of evolution is one of the most important scientific discoveries of all time. Unfortunately, however, the theory makes no provision for an afterlife. Consequently it has provoked more acrimonious debate than any other topic in science—so much so that some school districts in the United States have insisted on giving the “theory” of intelligent design (which is really just a fig leaf for creationism) equal status in textbooks. As has been pointed out repeatedly by the British scientist and social critic Richard Dawkins, this is little different from giving equal status to the idea that the sun goes around Earth. At the time evolutionary theory was proposed—long before the discovery of DNA and the molecular machinery of life, back when paleontology had just barely begun to piece together the fossil record—the gaps in our knowledge were sufficiently large to leave room for honest doubt. That point is long past, but that doesn’t mean we have solved the entire puzzle. It would be arrogant for a scientist to deny that there are still many important questions about the evolution of the human mind and brain that remain unanswered. At the top of my list would be the following:

1. The hominin brain reached nearly its present size, and perhaps even its present intellectual capacity, about 300,000 years ago. Yet many of the attributes we regard as uniquely human—such as toolmaking, fire building, art, music, and perhaps even full-blown language—appeared only much later, around 75,000 years ago. Why? What was the brain doing during that long incubation period? Why did it take so long for all this latent potential to blossom, and then why did it blossom so suddenly? Given that natural selection can only select expressed abilities, not latent ones, how did all this latent potential get built up in the first place? I shall call this “Wallace’s problem” after the Victorian naturalist Alfred Russel Wallace, who first proposed it when discussing the origins of language:

The lowest savages with the least copious vocabularies [have] the capacity of uttering a variety of distinct articulate sounds and of applying them to an almost infinite amount of modulation and inflection [which] is not in any way inferior to that of the higher [European] races. An instrument has been developed in advance of the needs of its possessor.