"Teaching, by which I mean actively setting out to educate another individual, is rare in nature. Nonhuman animals assist one another in alternative ways, such as provisioning with food or collaborating in an alliance, but they mostly aid their offspring or close relatives, who share their genes and hence also possess their tendency to help.

Yet in our species, dedicated teachers devote vast amounts of time and effort with children entirely unrelated to them, helping them to acquire knowledge, in spite of the fact that this does not inherently increase a teacher’s evolutionary fitness.

Pointing out that teachers are paid, which might be regarded as a form of trade (i.e., goods for work), only trivializes this mystery. The pound coin or dollar bill have no intrinsic value, the money in our bank account has a largely virtual existence, and the banking system is an unfathomably complex institution. Explaining how money or financial markets came into existence is no easier than explaining why schoolteachers will coach unrelated pupils."