Most primates have a sense of who their mother is. Some have a sense of fatherhood, or at least the-big-guy-who-hangs-around-and-doesn’t-kill-me-hood. Many have a sense of siblinghood, or at least of their half-siblings who haven’t moved away. Some have a sense of “mom’s sister” or other maternal relations, but generally speaking, primate kinship beyond these is subtle at best.

While burning and cutting were certainly crucial technological developments in the ultimate evolutionary success of our lineage, an equally important invention was the family. Unfortunately, social relations are much harder to find in the archaeological record than tools and hearths, so it scarcely gets the attention it merits. Nevertheless, a million and a half years ago, an unusual creature was inhabiting Africa and western Asia. Unlike other apes, it lived on the ground, as its ancestors had been doing with increasing anatomical specialization for a few million years.