They were evolved for a world in which people lived in very small groups, rarely met anybody who was terribly different from themselves, had rather short lives in which there were few choices and the highest priority was to eat and mate today.
Van evolucionar per a un món en el qual la gent vivia en grups molt petits, rarament es trobaven amb algú que fos terriblement diferent d'ells mateixos, tenien vides relativament curtes en les quals hi havia poques ocasions per escollir i on la més alta prioritat era menjar i aparellar-se avui.