How can we live without a condom?

Anthropology: Without a Condom to Monogamy: Why Do We Live in Couples?

In most small cultures, men live with several women. But seen globally, polygamy is rather rare, in large societies we have made monogamy the norm. But why actually?

Because gonorrhea, syphilis and co. Otherwise deprive our large societies of their children's blessings. In short, this is the essence of a study that Chris Bauch and Richard McElreath are now presenting in Nature Communications. They simulated on the computer how sexually transmitted diseases spread. They want to provide a new explanation for why monogamy was able to prevail among our ancestors.

They found that when people live together in small groups of a few dozen individuals, spontaneously occurring sexually transmitted diseases disappear sooner or later from the community - even if the people live polygamously. From a group size of 300 people, venereal diseases become a permanent problem, which means that a certain proportion of the group always has an illness.

Normally, it would be evolutionarily more favorable if a man lived with several women. However, diseases such as gonorrhea or chlamydiosis can clog the fallopian tubes, making women sterile. Syphilis destroys the central nervous system in the late stages and can be fatal as a result. If a man now lives monogamous and enforces this also with other group members, these diseases can no longer spread as strongly.

Up until now, anthropologists believed that it was more advantageous, especially for women, to live monogamous because the man could thus better support them in raising children. Or that men are in competition with one another and therefore shield their partner from rivals.

Imposing norms costs

With the latter strategy, however, the group pays with a lower birth rate, especially when the men impose their own approach on their peers (research speaks of "costly punishment"). For this reason, the evolutionary benefit of monogamy was rather unclear to anthropologists, and it was already suspected that sexually transmitted diseases could play a role in it.