And I end with one of the strangest of the consequences of sex: that the choosiness of human beings in picking their mates has driven the human mind … - Matt Ridley

The more competitive nature of men is a consequence of sexual selection. Men have evolved to live dangerously because success in competition or battle used to lead to more or better sexual conquests and more surviving children. Women who live dangerously merely put at risk those children they already have. Likewise, the intimate connection between female beauty and female reproductive potential (beautiful women are almost by definition young and healthy; compared with older women, they are therefore both more fertile and have a longer reproductive life ahead of them) is a consequence of sexual selection acting on both men’s psyches and women’s bodies. Each sex shapes the other. Women have hourglass-shaped bodies because men have preferred them that way. Men have an aggressive nature because women have preferred them that way (or have allowed aggressive men to defeat other men in contests over women—it amounts to the same thing).

It was these Prussian schools that introduced many of the features we now take for granted. There was teaching by year group rather than by ability, which made sense if the aim was to produce military recruits rather than rounded citizens. There was formal pedagogy, in which children sat at rows of desks in front of standing teachers, rather than, say, walking around together in the ancient Greek fashion. There was the set school day, punctuated by the ringing of bells. There was a predetermined syllabus, rather than open-ended learning. There was the habit of doing several subjects in one day, rather than sticking to one subject for more than a day. These features make sense, argues Davies, if you wish to mould people into suitable recruits for a conscript army to fight Napoleon.

The struggle for existence never gets easier. However well a species may adapt to its environment, it can never relax, because its competitors and its enemies are also adapting to their niches. Survival is a zero-sum game.