top of page
  • Writer's pictureDavid Williams

The Science of Love, by David Williams

When it comes to love, what’s “natural” for we homo sapiens? What makes us feel good? What’s right and what’s wrong? 16th century philosopher, David Hume, brought up the problem known as the Is-Ought Argument, which basically states, how can we know what we ought to do based on what is? Eventually, this argument was used by others to discuss nature itself, with the end result being that just because something occurs in nature, it doesn’t mean that it should be that way. This led to notion that we can derive nothing about morality or ethics from nature. Just because animals eat each other, for example, doesn’t mean we should do the same. But with the rise of Biology and eventually Neuroscience, it has become more and more apparent that altruistic behavior, compassion, kindness, even love, do have a Biological root. They didn’t spring out of nowhere. Our brains are not blank slates shaped by culture alone (as was the belief by most in academia for decades—and still is in many quarters), but the truth is we are wired from evolution to behave, act, and think in certain ways and not others. Love itself derives from a mix of neurochemicals, such as dopamine, oxytocin, vasopressin, serotonin, and others, that shape our feelings, thoughts, and desires. Darwin, himself, saw that the beginnings of love had to have developed from the bonds between mother and their young, which we see in innumerable species, and that the root of human love and affection also came initially out of the mother-child connection.

Affection, kindness, compassion, empathy, and the neurochemicals underlying them are certainly part of the human story, as well as that of all other primates. But why did love in humans become so complicated and multi-dimensional when our closest relatives do not engage in the protracted love behavior and attachment we humans do?

Love is not limited to humans. Very strong bonds of attachment form between mating animals of many species, though monogamy is still a mystery to biologists. From a numbers game, promiscuity offers many more chances for survival and dispersal of one’s genes. In addition, promiscuity leads to greater genetic variety, that has advantages for fighting disease. (Scientists now believe that the reason sex itself developed in nature is for this very reason. By a male and female putting their genes together, much more variation exists in their offspring than would be the case if asexual reproduction—which predates sex and is still seen in numerous plants and animals—were the case.

But the mating strategy of monogamy does allow for two parents to concentrate on their offspring, who are little packages of the parental DNA. And in the case of many bird species, monogamy is a necessity, as eggs have to be incubated; someone must sit on them at all times. But that “someone” also has to eat, so a system of pair-bonding was the easiest solution in nature.

Until recently, scientists believed that many species of birds were monogamous and faithful, but DNA analysis showed that thought to be naïve. It turns out that many avian females “cheat.” The female has a desire for the male with the flashiest feathers, as these are markers for fitness, but these males make terrible “husbands.” They know they are good looking and desirable, and they can mate with as many females as they choose, but they have no desire to sit on eggs. The drab male makes a better, more reliable partner. He will sit on the eggs and attend to the young. The female picks him for his fidelity and ability to provide, but (in some species up to 70%) she will still risk having a fling with the “stud.” But this is dangerous. For if the drab husband discovers infidelity, he is gone. He does not want to sit on eggs invested with another male’s DNA. So the game of Peyton Place is played out continually in bird communities around the world. If the female is not caught, she can have her cake and eat it too, but the stakes are high, for if she is caught having an “affair,” her eggs will die and her DNA will not enter into the gene pool. An evolutionary dead end.

Similar behavior has been found in mammals (including primates) through DNA analysis, where what looks like faithful monogamy is actually not. This finding has required scientists to make a distinction between Social Monogamy (a pair that lives together where there is cheating) and Genetic Monogamy (a pair who lives together where no cheating occurs).

Truth is, only 10 – 15% of primates are monogamous, including Gibbons, Siamangs, Owl monkeys, and humans, with most the 300 or so monkey and ape species being promiscuous. Our closest relatives, Chimpanzees and Bonobos are completely promiscuous, with females mating with as many males as possible. (At the same time, dominant males do get first access and a much better chance of spreading their genes, and vying for dominance is a central obsession for males). The mating act in chimps takes a few seconds, and there is no obvious emotional attachment, for as soon as consummation occurs the mated pair goes on their merry way as if nothing much ever happened. It is the mother who takes care of the eventual infant , and males play no role in raising the young.

In gorillas, the situation is that of a harem: one male has a number of females with whom he alone copulates. When young males reach adolescence must leave the colony and go off on their own so they cannot be in competition. And like hundreds of other animal species, when “kicked out” males bond together in homosexual groups, which ensues until that time some are lucky enough to establish their own harem of females. But there is no “romantic” attachment that develops between the dominant silverback and any of the females in his group.

Our ancient ancestors were no doubt chimpanzee-like in their behavior, and promiscuous. So what happened to change this, and when? (According to DNA analysis, we and chimpanzees diverged some 6 million years ago). The size difference between males and females (sexual dimorphism) is one indicator of sexual behavior. Gorillas and Orangutans have the greatest size difference, and they both have harem structures, as well as teeny testicles—their sperm don’t have to compete. Chimps, who are promiscuous—are in between gorillas and humans in overall relative size between males and females, and the males have absolutely enormous testicles. Their sperm must compete. Humans have the least sexual dimorphism of the great apes, males and females are slightly different in size, and humans tend to be pair-bonded. Human males have testicles larger than Gorillas but much smaller than chimps. Based on sexual dimorphism, evidence suggest that this pattern goes back some two million years, beginning with Homo Erectus, and existed in both Neanderthal and Homo Sapiens populations. So, it’s likely that we’ve been pair bonding for a significant amount of time.

If our ancestors began moving from promiscuity to pair bonding, the big question is why? Every society on earth has pair bonding, but then again, while the “norm” for humans, pair bonding (genetic monogamy) is not practiced in all situations, as our species has sexual mating patterns across the board: harems (one male with many females with whom he exclusively mates), polygamy (one man with multiple wives—two or more), polyandry (one woman with multiple husbands--extremely rare), and various types of promiscuity that include extra-marital affairs while within a pair bond (social monogamy), casual sexual partners (such as paid prostitutes, which were allowed in many societies, but only for men), and homosexual partners that may be exclusive or not.

Directly related to sex in the animal kingdom is the question of paternity. Male gorillas, lions, and many other males animals, are known to kill younger offspring not their own when they take over a colony, thereby guaranteeing that the next pregnancies will be of their DNA and not that of other males. For humans, we have countless cultural artifacts for guaranteeing fidelity, and it is for this reason that the obsession with virginity occurs in virtually every culture on earth. Whether it be the Virgin Mary, or the White Buffalo Calf Maiden, the cult of the virgin is universal. In addition, cultural practices, such as marriage, religion, chastity belts, and symbols like the wedding ring, are there to ensure that paternity is known and accurate. Interestingly enough, the main difference between the great apes and human beings is that males in our species take an active part in raising their children, nearly two decades, and fatherhood demands a tremendous cost from males (as well as females). There is much more at stake in paternity for human males than for male gorillas and chimps.

There are various theories to account for this shift toward pair bonding, the most prominent being the raising of children. Human beings are especially long-lived, and our offspring require years of education to prepare them for the complex social networks of human life and complications of culture. While other animals have some culture (learned behavior that is passed down to succeeding generations), nothing compares to the culture of homo sapiens—from language to technology— requiring the memorization of history, mythology, hunting and food gathering techniques, maps of landscapes, knowledge of plants and animals, seasons, agriculture, religion, law and codes of conduct, medicine, clothing and adornments, mating customs, as well as all the arts—music, ritual, painting, architecture, and writing. To exist as a human is not easy. Thankfully, the unconscious parts of the brain handle much of the learning we need (for instance, no one has to teach us language, which should be the most difficult task of all to learn).

So, it was advantageous for children to have two parents instead of one. Those with two prospered more than those with one parent, and it was the two-parent genes that began to appear more and more frequently in the genome of our species, which gave rise to more and more pair-bonding. But the the earlier promiscuous tendency of our ancestors was not wiped out—rather a new layer of behavioral disposition was added on top of the old. When it comes to evolution, the old is never erased; the new is just added on. We also still carry many genes from the ancient past that are there, just turned off—such as having dense body hair—like our ape relatives. (One of the most surprising things scientists found when uncoding the human genome is that we share 50% of our genes with bananas, a very ancient relative. For almost all life on earth is related at the genetic level. Go back far enough and you find a blade of grass and a blue whale share a common ancestor).

Not only having two parents instead of one was beneficial, but having a grandmother was as well. The Grandmother Theory states that the reason we are so long-lived is because it was especially advantageous for early humans who had a grandmother to help with the children. A Grandmother freed a mother from having to watch a young child 24/7, allowing her to do other essential things, like gather food. Once again, those with living grandmothers tended to survive more than those without, and genes for longer life began to proliferate in our genome. You can’t have a grandmother without humans living longer, and this is what pushed us in an evolutionary direction to get older than our primate cousins. (The oldest known chimp lived to be 74 in captivity, while in the wild 40-50 is the typical life expectancy).

What all this means is that the human mating system is a mess—complicated, contradictory, a base of promiscuity going back 30 million years with a two-million old propensity for pair bonding built on top if it, and all of this influenced by culture, which is changing at the speed of light, compared to biology. Nature and Nurture. Truth is, we come by sexual confusion naturally. So, what is natural? What is right? And what is wrong?


Dr. Helen Fisher, one of the most respected researchers on the science of love, has come to the conclusion that there are 3 stages of love that are universal in the human species. She defines these as LUST, ATTRACTION, & ATTACHMENT.

The evolutionary dice are constantly at play, but there is never an end result in mind. What matters is each moment of survival and the survival of one’s genes into the future. Eons of time have gone into programming plants and animals for this way of being, and survival is the primary drive for all living things. Everything else we do is secondary--playing tennis, or guitar, getting a job, going on a vacation, reading a book. Whether any of us want to have genetic legacy or not, we are programmed for sex and reproduction. We don’t have to be conscious of it, for it’s automatic, like breathing air. Once ignited in a species, desire can take many twists and turns. For example, animals can, and do at times, become homosexual, but the underlying drive for all sex drive is still reproduction, the same as a heterosexual couple using birth control who are enjoying sex without any thought of conceiving a child. Nature made sex wondrous as a way of perpetuating life. If sex wasn’t the most “fun” thing in the universe everything would go extinct.

It is very important to understand the root motivations behind our behavior, which are hidden from consciousness but drive the whole show. Our genes are pushing us to be successful, to make money, to be attractive, vigorous, athletic, talented, because all of these are at work to make us desirable, to have greater sexual access, and to ensure our genetic legacy. Regardless of age, we still want to appear youthful, fertile, with our mojo intact.


Incredibly powerful chemicals evolved in our brains to ignite the process of Love, and that brain chemistry activates hormones in our bodies to make us feel. Throughout species, Testosterone and Estrogen are produced to make males and females fall in lust. This has nothing to do with long-term bonding, but it creates a frenzy of sexual desire. It is the basic engine of reproduction, revving everything in the body toward one act—that of copulation. Once the ball is rolling the ball has to go somewhere, but we humans are complicated, and lust alone does not necessarily lead to consummation. We have layer upon layer of culture, education, religious training, moral codes, conceived to keep our most base instincts at bay. The courtship process, that will ensue, is wired in us (and in other species) to put the brakes on—to prevent automatic intercourse. And first, the female must decide if a tryst is worth her time and energy or if it will be a dangerous trap leaving her with no one to sit on the eggs. Lust is the beginning of madness—Romeo, having just broken up with his previous girlfriend, now sees Juliet, and soon after initially lusting for her, he is hooked—

Arise, fair sun, and kill the envious moon, Who is already sick and pale with grief That thou, her maid, art far more fair than she. . . . The brightness of her cheek would shame those stars As daylight doth a lamp; her eye in heaven Would through the airy region stream so bright That birds would sing and think it were not night. (II. ii. 2-6, 19-23)


The second stage of love consists of both euphoria and agony as new brain chemicals emerge that make us crave our beloved and pine when he or she is gone.

People become extremely energized, mad, obsessive, without sleeping or eating (and indeed, there are many traits in this phase that actually mirror insanity).

Testosterone and Estrogen

These are the underlying engines that motivate sexual desire. The hypothalamus of the brain stimulates the sex hormones, with both playing a part in men and women (testosterone increases sexual desire in males and females). Men produce 10 times more testosterone than women.


Known as noradrenalin, this hormone (along with its close relative, Dopamine) brings on giddy, euphoric behavior, an increase in energy, alertness, and also leads to decreased appetite and insomnia. This hormone makes the heart race—brings on feelings invincibility as the hormone circulates throughout the body, making all systems ready for consummation.


This chemical fuels pursuit, reward, chase, makes us perceive a target—wanting the bull’s eye. More powerful than cocaine, it makes the object of one’s desire seem the most rare, the fairest in the land, without flaws. And at this point the brain actually shuts down critical thinking that would sow any doubt regarding one’s love—nature’s way of moving the reproductive process along to its natural conclusion—pregnancy. Dopamine creates the bliss of the Honeymoon Phase, with cooing, pet name calling, cuddling, and an intimacy that excludes others, but eventually dopamine levels decrease to normal levels, sinking to the lowest point at about 4 years, which leads to a decline in attraction.

(Helen Fisher has found, through studying tribal societies around the world, that this is a corresponding sharp increase in divorce at 4 years, which also coincides with the child being old enough to no longer need parents keeping a 24/7 watch. At this point, the child can join the gang of other kids in the village during the day, playing with them, which takes some of the burden away from the parents).


Oddly enough, serotonin levels drop during the phase of Attraction. People with OCD also have low serotonin, and the brain in now in a similar state of obsession over the beloved. The presence of the beloved is the only the cure for this particular disease. Helen Fisher has warned that Prozac and other anti-depressants that boost serotonin levels actually hinder the process of Love by blunting the obsession necessary to bring a relationship to fruition. The artificial drug chemically takes the place of one’s lover and the brain no longer senses the need for the real thing.



This chemical, instrumental to the bonding of mother and child is also the brain neurochemical that facilitates us bonding with anyone, essential to love. As Darwin pointed out, the mother/child connection is the beginning of love across species, and evolution has used this neurochemical throughout the animal kingdom to fortify relationships. It is released in mammals through breast-feeding, orgasm, and through touch. It is the essential glue holding people and social animals

together. But this powerful neurochemical can also lead to extreme jealousy, over-attachment, exclusion of others, clinging behavior, and it can work to undermine the pair-bond if not controlled. Nature is never a perfect system, never designed, but only an ongoing experiment built upon those who survive, for whatever reason. It is their genes who enter into the future. As we have seen, we come by our conflicts naturally.


Vasopressin is the hormone that helps to determine monogamous or promiscuous relationships. While both males and females have vasopressin, it is more prominent in males due to the way it interacts with testosterone. Studies in voles showed that variations in in receptors between highly related species (meadow voles and prairie voles) lead to promiscuous or monogamous behavior (prairie being strictly monogamous). Variations in gene coding for vasopressin in humans also help determine if a man will tend toward faithfulness or not. (Variations in gene RS3 334 affect how men bond with their partners).


When things fall apart, the brain goes into physical pain that’s the same as getting off an addictive drug or behavior. This is real. At the same time, those regions of the brain that activate attachment, craving, longing, and romantic love, are all still alive, so this is a complete breakdown and descent into madness. It’s not all in your head. Your brain and body are under assault, but the pain will decrease over time. There are strategies one can employ to help in the recovery.

Nature has programmed us for love as part of the mating game, and everyone naturally has the disposition for falling into love addiction. Love evolved in order for a couple to stay together to raise a child, and there are few things more powerful. This is why a breakup can seem unbearable and become one of the most painful things that humans endure. Almost all the Blues songs are about love gone wrong, and poets/songwriters from every culture have dealt with the agony of love through the arts.


While evolution and biology have programmed we humans to go through specific sequences when it comes to love, culture is also a constant that tempers innate impulses. Still, in societies that deny romantic love and freedom to choose, with arranged marriages and stultifying proscriptions for how women and men must behave, the ancient biological patterns still exist, and they will find a way. A remarkable collection (Songs of Love and War) of contemporary songs from Afghan women who are forced into arranged marriages, whose husbands and sons beat them, and who are made to work in the most incomprehensible conditions where no love exists, shows that even in such a deadening culture where women are never exposed to models of romantic love there is still an incredible longing for it. In this culture, where women see their only way out as suicide, they still write wrench- ing love songs that almost always describe illicit affairs, defying all the powers that be and putting themselves in jeopardy:

You were hiding behind the door,

I was stroking my naked breasts

and you caught sight of me.

I will gladly give you my mouth,

But why stir my pitcher?

Here I am now, all wet.

First take me into your arms and hold me close,

Only then will you be

able to join my velvet thighs.

Current science shows that our desire for and reasons for selecting mates involves much more than “rational” choices consciously made by family members or even the lovers themselves. These songs attest to the more powerful and ancient set of biological impulses that are set in motion during puberty. As mentioned previously, longing for romantic love is a universal human phenomenon. While love is built upon the brain-wiring foundations for attachment we see in other animals, in humans that neural wiring has been altered over thousands of generations to become unique. It is nature’s way of flooding the brain with chemicals for both mating and attachment, leading to a kind of intimacy that goes far beyond anything else in the animal world. But it’s a game of high stakes, constant assessment and reassessment, a psychological thriller full of paranoia, all-consuming lust, jealousy, and madness. As Shakespeare said, “If thou remember’st not the slightest folly/That ever love did make thee run into/ Thou hast not loved.” Shakespeare constantly parodied the insanity of love in his plays, from Romeo and Juliet to Twelfth Night, showing us in dramatic form what fools we can become.

In today’s technological stew, with the related necessity of people needing to develop careers that take many years to foster, culture is shaping how the biology of love will be played out. For many women and men the demands of college and career mean that childbearing is put off to a later and later date. The exception is with those involved in fundamental religious communities where sex before marriage is still frowned upon and early marriage is promoted. But the greater societal shift in dating practices seems to mimic those of the Playboy era of the 50s and the Free Sex era of the 60s, with some alterations. People in their teens and twenties tend to hang out in mixed groups where boys and girls are friends and equals (this is certainly a change from the earlier sexual revolutions, where women were still looked upon as second class citizens), and hookups are the name of the game. For many, a sexual encounter is seen as a thing of the moment, and the default expectation is that there isn’t any. The hookup culture attempts to keep emotional involvement to a minimum, lasting just the night. But, of course, neurochemicals will be released during sex that still have a powerful affect toward attachment and must be kept at bay through conscious attempts to override them. When asked, most young women in their 20s involved in hookups still dream of an eventual marriage in the future, with a cake, gown, and a faithful husband. So the dream of monogamy is not dead. While another factor in today’s non-attached love culture, as mentioned previously, is the widespread use of serotonin-uptake-inhibitors, such as Prozac and Zoloft, where the neurochemical takes the place of flesh and blood interactions.

The prevalence of divorce has also changed the way people in Western culture deal with love. With religion greatly diminished, there is freedom to break up a relationship, even one with kids, that did not exist a generation or two ago. The definition of family has also changed, now including “blended” families and familial relationship patterns such as polygamy, serial monogamy, gay and lesbian marriage, and more. Humans have always been experimental, but now our varieties of entanglement are relatively out in the open. One informant from Dallas, said that in upper class circles of that notoriously conservative city the trend today is for people to stay married while still having multiple sexual partners on the side. These are still somewhat covert, yet they seem to be commonplace and generally accepted. Ironically, as different types of pairing are allowed, at the same time, across the United States more people are living alone than ever have before, and more people are having less sex than every before. At the same time, an odd exception is the elderly in senior communitiies, where venereal diseases has skyrocketed as the bounds of traditional relationships, through either death or divorce, have left many seniors free to pursue numerous sexual partners.

But probably nothing has changed the culture of love and courtship in the last 15 years as much as Online dating, with 40 million American now participating in online dating sites, with nearly early 19% of today’s relationships being formed initially online, compared to friends (17%), college acquaintances (15%), and people met at work (12%). Many online daters are people who have raised families, gotten divorced, and are now finding themselves in unknown territory, where rules and expectations are not clear. As digital media has changed the way we read (our eyes quickly scanning the screen, picking up keywords without reading closely), we also scan online dating sites, glancing at photos (mostly of poor quality), while trying to assess if this person would be a good date, a one-night stand, or a permanent partner. It’s put millions of human beings in a quandary. For, are our intuitions sound or mere fantasy? Is there any correlation between a face shot and what we believe that face to represent? Studies have shown that (of course) when we see a very good-looking individual the neurochemical dopamine is released into the brain. (By now, most people are aware of the fact that “beauty” (symmetry, the golden triangle, youth, clear skin, attractive body proportions often signal health and fertility, which is why nature made us find these traits attractive in the first place). There is a visceral effect in the brain and body when we see a pretty person. But of course that does not predict that a successful relationship will ensue. Beyond the lust stage there has to be more—an intellectual and emotional connection built upon numerous components and interests.

Still, looks matter. Anyone who has embarked upon online dating has experienced the scan—the half second evaluations that trigger a yes or no. We think that we are making logical judgements based upon reliable intuitions, that someone looks intelligent or not, for instance. But studies have found that women’s intuitions in correlating facial traits with intelligence in men tend to be accurate, the opposite is not true for men. A possible explanation for this has to do with the different mating strategies men and women employ, due to biology and evolution.

Women prefer dominant men as extra-pair sexual partners while at the same time they seek men who are more willing to invest in their offspring as long-term or social partners [52]. It is known that while in the fertile phase of cycle and probably in search of good genes, women prefer creative intelligence to wealth especially in short-term mating [18]. On the other hand, a woman seeking a long term relationship could prefer a less intelligent but honest man, who compensates by long term provisioning, protection and a greater investment in childrearing. (

Overall, studies of online dating show that men judge more on looks, while women judge more on income. ) And this follows a pattern seen in all dating throughout the world. As a woman finds herself closer to commitment, financial security trumps looks and intelligence, while men remain constant on looks as their number one criteria.


bottom of page