If you dropped a dozen human toddlers on a beautiful Polynesian island with shelter and enough to eat, but no computers, no cell phones, and no metal tools, would they grow up to be like humans we recognize or like other primates? Would they invent language? Without the magic sauce of culture and technology, would humans be that different from chimpanzees?
Nobody knows. (Ethics bars the toddler test.) Since the early 1970s, scientists across the biological sciences keep stumbling on the same hint over and over again: we’re different but not nearly as different as we thought. Neuroscientists, geneticists, and anthropologists have all given the question of human uniqueness a go, seeking special brain regions, unique genes, and human-specific behaviors, and, instead, finding more evidence for common threads across species.
In the old days, the main hypotheses were behavioral. “Humans are the only animals to use tools.” “Humans are the only animals to have culture.” “Humans are the only animals to teach their young.” But over time most of those guesses have turned out to be wrong. It’s become even more mysterious because almost everything we have found points in the opposite direction, toward what biologists call conservation—evolution’s tendency to use many of the same genes, neurotransmitters, and brain circuits, over and over again.