Human EvolutionThere is an interesting principle in biology, named Haeckel’s Recapitulation Theory: ontogeny recapitulates phylogeny. In simple terms, that means that you can read the whole evolutionary tree leading to a species just by looking at successive development stages of the fetus. We start looking like single-cell individuals, “evolve” into bunches of cells, eventually “turn” into fish, then lizards, then monkeys, etc.

It’s not as simple as that, and the principle/theory has been refuted/rejected. But the idea has wider applications than just in evolutionary biology. In general, I’d say, the notion is that the behavior of the (averaged) individual allows reconstruction of the group’s creation/formation/development.

Humans are a weird bunch. We have all sorts of odd characteristics that make us stand out even with respect to our closest relatives, The size of our brains is what we are most proud of, but there is hairlessness, too; upright walking and long-distance running; our opportunistic digestive tract, not specialized for anything, and unable to digest anything that requires complexity; and more.

The picture that emerges is fairly clear: we evolved in a temperate climate with little seasonal variation, with a diverse food supply, none of whose components could be counted on in the long term. The ability to run indicates that we were group hunters, since we are not fast enough to outrun prey or hunters.

One of the things that is strangest about humans, though, is our sexuality. You see, life usually has two strategies: continual mating, where offspring is generated indiscriminately throughout the year; and seasonal mating, where sex happens at a specific time of the year.

Typically, the strategy picked indicates the environment in which the life form lives. If there is strong seasonal change, it is advisable to time pregnancy and birth so that it matches availability of food and environmental protection. If there isn’t, then it is smarter to have any sexual encounter be a chance for reproduction, since you don’t know whether there is going to be another day.

Humans, though, have the strangest method: our females are fertile for a few days every month, and infertile otherwise. That seems to be the stupidest combination possible: it limits the chance to reproduce without giving any obvious advantage in timing of offspring.