Our ancestors didn’t choose monogamy out of anything so high-minded as love or religion, according to a new study published Tuesday.
Published in the journal Nature Communications, the new study found that the spread of sexually-transmitted diseases and peer pressure may have led to monogamy being the norm in almost all modern societies.
Study scientists used computer modeling solutions to replicate the development of several social mating habits in human populations derived from demographic and disease propagation variables.
“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,” study author Chris Bauch, a professor of applied mathematics at the University of Waterloo, said in a news release. “Our research illustrates how mathematical models are not only used to predict the future, but also to understand the past.”
Study scientists discovered that when populations become large, the existence of STDs lowers fertility rates more among males with numerous partners, therefore shifting which mating behavior turns out to be most helpful to individuals and groups.
In early hunter-gatherer populations, it was standard for a few males to monopolize mating with numerous females to be able to raise their amount of offspring. In these small communities where there is a maximum of 30 sexually-mature individuals, STD outbreaks were likely short-lived and tended to not have as noteworthy an impact on the population.
Yet, as societies developed around agriculture and population sizes grew, the study found the prevalence of STDs was higher amongst polygamist systems that overlapped. With the lack of modern medicines, infertility from these infections would probably have been high, the study found. This made it more beneficial for males to mate monogamously, and therefore, to penalize other males who did not. Communities that enforced monogamy could therefore outcompeted communities lacking this value.
“Our social norms did not develop in complete isolation from what was happening in our natural environment. On the contrary, we can’t understand social norms without understanding their origins in our natural environment,” Bauch said. “Our social norms were shaped by our natural environment. In turn, the environment is shaped by our social norms, as we are increasingly recognizing.”