There is no greater mystery in human evolution than the origins of our sexuality. Following the trail of clues available researchers have independently concluded that humans evolved through systems of monogamy, polygamy, as well as polyamory. However, only one can be the culprit. Like a detective interrogating multiple suspects, the solution ultimately depends on which account you’re willing to believe.
In 2009 Owen Lovejoy made the case for monogamy based on the fossil remains of the early human ancestor Ardipithecus ramidus. Meanwhile, Christopher Ryan and Cacilda Jethá have argued that polyamory (or, more precisely, a multimale-multifemale mating system) is the most likely scenario from an analysis that emphasized anthropology, behavioral biology, and physiology. To further complicate matters the third suspect in this mystery, polygamy, has been the conclusion from scientists conducting DNA analyses. These conflicting accounts therefore require careful detective work in order to determine which story is the most convincing.
Polygyny (the single male-multifemale version of polygamy) is most well known among primates such as baboons or gorillas. These are the species that have been (incorrectly) described as living in “harems,” and are often easy to identify since the males can be up to twice the size of females. Many anthropological accounts, most famously George Murdock’s Ethnographic Atlas, have suggested that the human species is “moderately polygynous” since the majority of studied societies practice polygynous marriage (982 out of 1157 according to Murdock’s account).