Some scientists have argued that human beings evolved to be monogamous, while others claim that we evolved to be non-monogamous. So which view is correct? According to recent research on the subject, the answer isn’t one or the other because it’s a bit more complicated than that.
Rather than all of us having the same relationship orientation, research increasingly suggests that some people are predisposed to different styles of mating. One of the most provocative pieces of evidence supporting this idea comes from a neuroscience study recently published in the Archives of Sexual Behavior, which suggests that monogamous and non-monogamous orientations just might be "wired" into our brains.
In this study, researchers put 20 heterosexual men (aged 34 on average) in fMRI scanners and looked at what went on in their brains while they viewed different kinds of images. These men were carefully selected to ensure that half were "highly monogamous," whereas the other half were “highly non-monogamous.”
To qualify as "highly monogamous," guys had to say that they’d never been in an open relationship, had never cheated (and had no desire to do so), rarely fantasized about women other than their current partner, and reported fewer sex partners than the average person—specifically, fewer than five. For comparison purposes, data from the General Social Survey reveals that Americans today report an average of about 11 sex partners.
By contrast, to qualify as "highly non-monogamous," guys had to report experience with both open relationships and infidelity, express a preference for having multiple sexual partners at the same time, and be more sexually experienced than average. These men reported an average of 30 previous sex partners.
While inside the fMRI machine, participants were briefly shown blocks of images that varied in content. Some image blocks were sexual, featuring nude men and women engaged in vaginal intercourse. Others were romantic, featuring clothed men and women doing things like hugging or holding hands. And yet others were neutral. Some of the neutral images featured pairs of people doing everyday things that weren’t romantic or sexual in nature (like barbecuing), while others were nature scenes that didn’t include any people at all.
Researchers then compared the patterns of brain activation they observed. What they found was that men, regardless of whether they were monogamous or non-monogamous, demonstrated significant activation of the brain’s reward pathways when viewing sexual images. In other words—and perhaps unsurprisingly—both groups of guys found the sexual images to be about equally pleasing.