In our mythologies, there’s often a singular moment when we became “human.” Eve plucked the fruit of the tree of knowledge and gained awareness of good and evil. Prometheus created men from clay and gave them fire. But in the modern origin story, evolution, there’s no defining moment of creation. Instead, humans emerged gradually, generation by generation, from earlier species.
As with any other complex adaptation—a bird’s wing, a whale’s fluke, our own fingers—our humanity evolved step by step, over millions of years. Mutations appeared in our DNA, spread through the population, our ancestors slowly became something more like us and, finally, we appeared.
Strange Apes, But Still Apes
People are animals, but we’re unlike other animals. We have complex languages that let us articulate and communicate ideas. We’re creative: we make art, music, tools. Our imaginations let us think up worlds that once existed, dream up worlds that might yet exist, and reorder the external world according to those thoughts. Our social lives are complex networks of families, friends, and tribes, linked by a sense of responsibility towards each other. We also have awareness of ourselves and our universe: sentience, sapience, consciousness, whatever you call it.
And yet the distinction between ourselves and other animals is, arguably, artificial. Animals are more like humans than we might think—or like to think. Almost all behavior we once considered unique to ourselves is seen in animals, even if they’re less well developed.
That’s especially true of the great apes. Chimps, for example, have simple gestural and verbal communication. They make crude tools, even weapons, and different groups have different suites of tools—distinct cultures. Chimps also have complex social lives and cooperate with each other.
As Darwin noted in Descent of Man, almost everything odd about Homo sapiens—emotion, cognition, language, tools, society—exists, in some primitive form, in other animals. We’re different, but less different than we think.
And in the past, some species were far more like us than other apes: Ardipithecus, Australopithecus, Homo erectus, and Neanderthals. Homo sapiens is the only survivor of a once diverse group of humans and human-like apes, the hominins, which includes around 20 known species and probably dozens of unknown species.
The extinction of those other hominins wiped out all the species that were intermediate between ourselves and other apes, creating the impression that some vast, unbridgeable gulf separates us from the rest of life on Earth. But the division would be far less clear if those species still existed. What looks like a bright, sharp dividing line is really an artefact of extinction.
The discovery of these extinct species now blurs that line again and shows how the distance between us and other animals was crossed—gradually, over millennia.
The Evolution of Humanity
Our lineage probably split from the chimpanzees around six million years ago. These first hominins, members of the human line, would barely have seemed human, however. For the first few million years, hominin evolution was slow.
The first big change was walking upright, which let hominins move away from forests into more open grassland and bush. But if they walked like us, nothing else suggests the first hominins were any more human than chimps or gorillas. Ardipithecus, the earliest well-known hominin, had a brain that was slightly smaller than a chimp’s, and there’s no evidence they used tools.
In the next million years, Australopithecus appeared. Australopithecus had a slightly larger brain; larger than a chimp’s, still smaller than a gorilla’s. It made slightly more sophisticated tools than chimps, using sharp stones to butcher animals.
Then came Homo habilis. For the first time, hominin brain size exceeded that of other apes. Tools like stone flakes, hammer stones, and “choppers” became much more complex. After that, around two million years ago, human evolu...
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