Definition
Evolution is the change in the heritable characteristics of populations across generations. Charles Darwin's central insight was that this change is driven, in large part, by natural selection: variants that survive and reproduce more successfully in a given environment leave more copies of themselves in the next generation, so the population's makeup shifts over time.
For Harari, evolution is not just the topic of one topic but the precondition of the whole book. Homo sapiens is a species. The body, the brain, the social instincts, and the very capacity for shared fiction are evolved traits with deep histories that long predate any culture.
Why it matters
How it works
Three ingredients are needed: variation (organisms differ), heritability (some of that difference passes to offspring), and differential reproduction (some variants leave more offspring than others). Where all three hold, the population's traits drift over generations toward whatever the environment rewards.
This means evolution has no foresight and no preferred direction. It is responsive to the local moment. A trait that is adaptive in one environment may be neutral or harmful in another. The very same cognition that made Sapiens supremely successful as a forager now drives obesity epidemics in food-saturated societies.