According to a recent study from the University of Waterloo, monogamy became a social norm because of peer pressure and the spread of sexually transmitted infections.
Researchers Chris Bauch, an applied mathematician at the University of Waterloo, and Richard McElreath, an evolutionary ecologist at the Max Planck Institute for Evolutionary Anthropology in Germany, suggest that early civilizations feared what sexually transmitted infections could do to growing populations and therefore punished behaviour that they believed promoted the spread of STIs.
"This research shows how events in natural systems, such as the spread of contagious diseases, can strongly influence the development of social norms and in particular our group-oriented judgments," Bauch said in a press release.
Bauch and McElreath created a computer simulation that combined various demographic and geographic data along with mating behaviours to compare STI impact across different communities.
Through their research the scientists found that larger populations showed an increased presence of STIs and decreased fertility rates. Alternatively in smaller groups of no more than 30 sexually active adults, STI outbreaks not only remained contained they also appeared to have a smaller impact on population.
Monogamy was thus seen as imperative for nation-building and stability so any deviations from, or threats to it, were punished or ostracized.
"The change in behaviour began with the advent of agriculture, when humans began living in larger residential groups than was typical of hunter-gatherers. In the simulation model, individuals imitated strategies that produced the largest number of offspring," Bauch said to HuffPost Canada via email.
While Bauch and McElreath propose that punishment of individuals is what led to monogamy in prehistoric populations, they also note other factors involved in the shift to monogamy such as female choice and technological advances.