The Long Way Back to Ourselves

1.1

Why Us of All Species? Human Kinds and a Brain Too Expensive

This chapter corrects the assumption that only one kind of human was biologically possible, showing that four to six species overlapped on Earth as recently as 100,000 years ago, including the Denisovans, known almost entirely from a finger bone and teeth. You learn that the straight-line image of evolution is replaced by the idea of the genus Homo as a branching bush. It corrects, too, the assumption that a bigger brain made Homo sapiens the survivor: Neanderthals had larger brains, and a 2011 study failed to confirm that a shrinking gut financed our brain's growth. It ends with five competing, unresolved explanations for why sapiens alone survived, mostly concerning group size rather than raw intelligence.