It’s because other people have a major influence over our brain’s (and therefore our) well-being, and seldom is this more true than in romantic relationships.
Much of human culture seems dedicated to ending up in a long-term relationship, or acknowledging that you’re in one (see: Valentine’s Day, weddings, rom-coms, love ballads, the jewelry industry, a decent percentage of all poetry, country music, anniversary cards, the game “Mr. & Mrs.” and so on). Monogamy is not the norm among other primates14 and seems odd when you consider we live much longer than the average ape so could feasibly dabble with many more partners in the available time. If it’s all about “survival of the fittest,” making sure our genes propagate ahead of others, surely it would make more sense to reproduce with as many partners as possible, not stick to one person for our entire lives? But no, that’s exactly what we humans tend to do.
There are numerous theories as to why humans are seemingly compelled to form monogamous romantic relationships, involving biology, culture, environment and evolution. Some argue that monogamous relationships result in two parents caring for offspring rather than one, so said offspring have greater chance of survival.15 Others say it’s due to more cultural influences, such as religion and class systems wanting to keep wealth and influence within the same narrow familial range (you can’t make sure your family inherits your advantages if you can’t keep track of it).16 Another interesting new theory pins it on the influence of grandmothers acting as child carers, thus favoring the survival of long-term couples (even the most doting grandmother would probably balk at caring for the unfamiliar offspring of her own child’s ex).17
Whatever the initial cause, humans seem primed to seek out and form monogamous romantic relationships, and this is reflected in a number of weird things the brain does when we end up falling for someone.
Attraction is governed by many factors. Many species end up developing secondary sex characteristics, which are features that occur during sexual maturity but that aren’t directly involved in the reproductive process, for instance, a moose’s antlers or a peacock’s tail. They’re impressive and show how fit and healthy the individual creature is, but they don’t do much beyond that. Humans are no different. As adults we develop many features that are apparently largely for physically attracting others: the deep voice, enlarged frames and facial hair of men, or the protruding breasts and pronounced curves of women. None of these things are “essential,” but in the distant past some of our ancestors decided that’s what they wanted in a partner, and evolution took over from there. But then we end up with something of a chicken-and-egg scenario with regards to the brain, in that the human brain inherently finds certain features attractive because it has evolved to do so. Which came first, the attraction or the primitive brain’s recognition of it? Hard to say.
Everyone has his or her own preferences and types, as we all know, but there are general patterns. Some of the things we humans find attractive are predictable, like the physical features alluded to above. Others are attracted to a more cerebral quality, with a person’s wit or personality being the sexiest thing about them. A lot of variation is cultural, with what’s deemed attractive being heavily influenced by things such as the media or what’s considered “different.” Contrast the popularity of false tans in more Western cultures with the huge market for body whitening lotions in many Asian countries. Some things are just bizarre, such as research that suggests people are more attracted to individuals who resemble them,18 which harks back to the brain’s ego bias.
It’s important, however, to differentiate between a desire for sex, aka lust, and the deeper, more personal romantic attraction and bonding we associate with romance and love, things more often sought and found with long-term relationships. People can (and frequently do) enjoy purely physical sexual interactions with others that they have no real “fondness” for apart from an appreciation for their appearance, and even that’s not essential. Sex is a tricky thing to pin down with the brain as it underlies much of our adult thinking and behavior. But this section isn’t really about lust; we’re talking more about love, in the romantic sense, for one specific individual.
There’s a lot of evidence to suggest the brain does process these things differently. Studies by Bartels and Zeki suggest that when individuals who describe themselves as in love are shown images of their romantic partners, there is raised activity (not seen in lust or more platonic relationships) in a network of brain regions including the medial insula, anterior cingulate cortex, caudate nucleus and putamen. There was also lower activity in the posterior cingulate gyrus and in the amygdala. The posterior cingulate gyrus is often associated with painful emotion perception, so it makes sense that your loved one’s presence would shut this down a bit. The amygdala processes emotions and memory, but often for negative things such as fear and anger, so again it makes sense that it’s not so active now; people in committed relationships can often seem more relaxed and less bothered about day-to-day annoyances, regularly coming across as “smug” to the independent observer. There’s also diminished activity in regions including the prefrontal cortex, which is responsible for logic and rational decision-making.
Certain chemicals and transmitters are associated too.? Being in love seems to elevate dopamine activity in the reward pathway,20 meaning we experience pleasure in our partner’s presence, almost like a drug (see Chapter 8). And oxytocin is often referred to as “the love hormone” or similar, which is a ridiculous oversimplification of a complex substance, but it does seem to be elevated in people in relationships, and it has been linked to feelings of trust and connection in humans.21
This just the raw biological stuff that happens in our brains when we fall in love. There are many other things to consider, like the expanded sense of self and achievement that comes from being in a relationship. There’s the immense satisfaction and achievement that comes from having a whole other person value you so highly and want to be in your company in all manner of contexts. Given that most cultures invariably see being in a relationship as a universal goal or achievement (as any happily single person will tell you, usually through gritted teeth), there’s also advanced social standing from being in a couple.