Climate variation drove the evolution of our four basic temperaments.
While humans were evolving in Africa, the climate cycled from wet to dry and back again, over and over. In evolutionary terms, it did so quickly, every 20,000 years.
This meant that we had to switch back and forth between living in forests where food was abundant, and living on savannah plains where food was scarce. How did we adapt? Humans developed two mating strategies, one suited to the forest, the other to the savannah:
- Promiscuity was adaptive in the forest. Promiscuous mating leads to more children, who can populate a rainy forest ecosystem where food is abundant.
- Exclusivity worked better on the savannah. Exclusive mating produces fewer children, who won’t overpopulate a dry savannah ecosystem where food is scarce.
These two mating strategies are genetically “hard-wired” within us, and can be seen among hunter gatherer peoples today. Forest-dwelling hunter-gatherer peoples favor mating with several people, while savannah dwellers emphasize pairing off with one.
Because our mating genes evolved in response to environmental changes, they probably have environmental triggers. That is, a pregnant woman’s body “tells” a fetus: The climate is wet and there’s plenty of food. If you have Nymph/Satyr genes, it’s okay to turn them on. Because they had to persist through many generations, these genes probably work through dominant and recessive pairs, like the ones that make us left- or right-handed.
However our mating genes work, they involve Feminine and Masculine hormones. Higher oxytocin levels increase men’s sexual desire, while higher testosterone levels increase women’s promiscuity. That’s why moderate-testosterone Nymphs are attracted to moderate-oxytocin Satyrs, and minimal-testosterone Muses are drawn to minimal-oxytocin Centaurs.