According to evolutionary biologist Sergey Gavrilets, the modern family might look very different had some scrawny male hominids not found a clever workaround to having to physically compete against strong alpha males for mates. In his latest study published in the Proceedings of the National Academy of Sciences, Gavrilets suggests that weaker males, in lieu of being promiscuous, fawned over a single female. By providing her food, a male would earn that female’s trust and sexual fidelity. In this scenario, the pair’s offspring naturally benefited, as they were more likely to survive under the watchful gaze of two parents.
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So, let’s start by going back in time. Before monogamy and the nuclear family, how did hominids live?
Judging from the fact that our closest relatives are chimpanzees, I think we can expect that our social life was pretty similar to what they have now, which is basically small groups. As far as mating relationships are concerned, there is a very strong dominance hierarchy in chimpanzees, where alpha males completely dominate the group and get the majority of mating. It is a very despotic society, and I think that is what our ancestors had as well.
When do you start to see a transition from promiscuity to pair bonding?
We know that humans separated from chimps somewhere around 6 or 7 million years ago. In hunter-gatherer societies, typically, each man has a single wife. So it happened somewhere during this interval that is several million years long.
There was a series of papers in the journal Science three years ago that described a fossil, known as Ardipithecus ramidis, for the first time in detail. This fossil is 4.4 million years old, so about one million years older than [the famous hominid specimen named] Lucy. People claim that this new species already shows signs of significantly reduced competition between males. Both the sexual size dimorphism [or difference in size between males and females] and the size of the canine teeth are dramatically decreased. They are much smaller than you would typically see in species with very strong between-male competition. The claim that researchers made is that this pair bonding in our lineage is something that is more than 4 million years old.
As you say, it was a “social dilemma” for males to shift their focus from competing for mates to caring and providing for one mate and their collective offspring.
From an evolutionary point of view, everybody is interested in creating a number of surviving offspring. How can males do it? Well, one strategy for males is to mate with as many females as possible. We can have a lot of offspring, but we are going to completely neglect them.
On the other hand, there is an alternative strategy. Instead of maximizing the number of matings, you can maximize the investment in the offspring. This way, even if you have a small number of offspring, most of them survive, and you can be better off. That is basically the situation that I model in my paper.
One is beneficial for the male—to increase the number of matings. But, in this case, a lot of energy and effort is wasted on the competition. Then, there is this other strategy—investment in the offspring or in the females. This strategy will definitely be beneficial for the group as a whole, but because of this existing logic of competition in the group, males are forced to invest in a low fitness solution. They are forced to compete rather than to invest.