Sapiens: A Brief History of Humankind

by Yuval Noah Harari

It’s a common fallacy to envision these species as arranged in a straight line of descent, with Ergaster begetting Erectus, Erectus begetting the Neanderthals, and the Neanderthals evolving into us. This linear model gives the mistaken impression that at any particular moment only one type of human inhabited the earth, and that all earlier species were merely older models of ourselves. The truth is that from about 2 million years ago until around 10,000 years ago, the world was home, at one and the same time, to several human species. And why not? Today there are many species of bears: brown bears, black bears, grizzly bears, polar bears. The earth of a hundred millennia ago was walked by at least six different species of man.

In Homo sapiens, the brain accounts for about 2–3 per cent of total body weight, but it consumes 25 per cent of the body’s energy when the body is at rest.