The Social Roots of Human Evolution

The most obvious way to distinguish us humans from the millions of other species on Earth is by looking at the things we make. Even from thousands of miles away, our creations would be obvious to an alien naturalist passing by on an interstellar Beagle: the swarm of satellites, space stations, and bits of space junk orbiting the planet; the signs we leave on Earth’s face, from the Great Wall of China to the constellation of city lights glowing at night; the stream of transmissions–phone calls, cartoon shows, and the rest of our great telecommunication babble–beaming out into space.

Technology may be an obvious hallmark of humanity, but it’s not the only one. Compared to other animals, we are a supremely social species. We live in a global network of nations, alliances, tribes, clubs, friendships, corporations, leagues, unions, and secret societies. Our social nature would be much harder for our passing alien naturalist to detect, and yet the invisible links that bind us together are no less important to human nature than the highways or cities we may build for ourselves.

When we look back through time at the evolution of our own species, we are in the same plight as the alien naturalist. We can see vestiges of the technology of our ancestors; we can even touch them. As early as 2.5 million years ago, our ancestors were chipping away at stones to create blades for cutting the flesh from carcasses. By 1.5 million years ago, they were making powerful stone hand axes that they may have used not just for flesh‑cuffing, but for crafting other tools, like digging sticks. By 400,000 years ago, the oldest spears appear, and the technological record becomes more and more dense as it approaches the present day. No other animal has left behind signs of technology in the 4 billion years of life’s history on Earth. But while you can wrap your fingers around a million‑year‑old hand axe, you cannot touch the society of the person who crafted it or the experiences he or she had living in it.

Yet as difficult as it is to glimpse the social evolution of humans, scientists suspect that it was a crucial factor in the rise of our species–perhaps the crucial factor. Our chimplike ancestors had chimplike social lives, but 5 million years ago they branched away from other apes and began to explore a new ecological niche on the savannas of East Africa where their social lives became far more complex. Much of what makes humans special–our big brains, our intelligence, even our gift of language and our ability to use tools–may have evolved as a result. At the same time, the competition for mates and the struggle for reproductive success among these hominid ancestors of ours may have left their mark on our psychology, shaping our capacity for love, jealousy, and all our other emotions.