CHAPTER 3
IN THE LAST CHAPTER we saw that our ancestors who arrived in Europe around 40,000 years ago met Neanderthals. This turned out badly for the Neanderthals, as we killed them all off. But before we did, like the black widow spider, we had sex with them. Surprisingly, we are all descended from these couplings. Our DNA contains a small portion – around 1.8 per cent – of Neanderthal DNA. This idea that we would mate with hairy, brutish cavemen was derided by many scientists, as it was compared to us having sex with a chimpanzee. However, the evidence that we did is now compelling. What did we find attractive about them? Was it only women who were ovulating who found the cavemen attractive? How do we choose a prospective mate?
If you’re a man, should you spray yourself with Old Spice, put a Mont Blanc pen in your breast pocket with the snowflake logo clearly showing, make sure your waist/hip ratio is 9:10, drink neat whiskey and strut your stuff on the dance floor? The science behind attraction has been a hot topic of late, with some surprising and enlightening findings that get to the very essence of who we are as a species. And when you do choose a mate, what are the odds that you’ll stay faithful and have a happy relationship? Science might even have an answer to that.
The science of attraction is big business. Dating agencies have been around for a long time. In times past, the job of the matchmaker, who helped couples get together, was an important one. In the late 20th century someone invented speed-dating as a way to make the whole process more efficient. In ancient Rome, the god Cupid was thought to bring people together, as the process even then seemed mysterious. Why this person and not another? What dating agencies know is that interests, values and background are important. Although in a recent study, people filled in a detailed questionnaire about themselves and then, based on compatibility, predictions were made as to who might dig whom1. They were then put through a speed-dating process, and guess what? The predictions got it wrong. The authors of the study concluded that ‘compatibility elements of human mating are challenging to predict before two people meet’.
THE GOD OF LOVE SHOOTS AN ARROW AT THE LOVER, IN A 14TH-CENTURY DEPICTION OF THE LOVE POEM ‘ROMAN DE LA ROSE’.
We are, however, inclined to choose people like ourselves. In fact it has been shown that you are attracted to people who look like your own relatives2. First response: ew! Why this is the case isn’t clear, but it could be down to a lower risk of being rejected. If you choose someone very different from you, they might see you as being from another tribe and might worry that you are going to harm them. Or perhaps someone who looks like a relative is more likely to stick around and help you raise the baby. In one study, it was shown that we are attracted to people who look like our parents. People born to older parents are attracted to older people. Maybe they make us feel safe. When it comes to instant physical attraction we are often unable to explain why it happened. One problem is studying it in a scientific way. It’s almost impossible to replicate attraction in a laboratory context. Those bright lights and people in white coats are clearly off-putting. So what do we know about that moment when you see someone across a crowded room and think, hmmm, I like the look of that person?
First, there is our sense of smell. We find how other people smell either attractive or repellent. Welcome to the world of pheromones, the volatile chemicals that we exude mainly in our sweat. A lot of money has been spent on research into pheromones, as they could be the key to making perfumes more effective for attracting a mate. They are well known to play a role in the animal kingdom, so why not in humans? Female dogs in heat will release pheromones and male dogs many miles away can detect them and start howling. Insects mainly attract a mate by releasing pheromones. This type of communication is subconscious – we don’t even know that it’s happening.
One reasonably reputable study (and we must take these studies with a pinch of salt – or sweat) got men to sniff T-shirts from women at different times in their menstrual cycle. There was a statistically significant association with T-shirts being rated as smelling pleasant if the woman was ovulating (meaning that if sex should happen there’s a good chance that she will conceive)3. This makes sense (or scents?). The woman will want to attract a mate when one of her eggs can be fertilised, so her body makes a pheromone which draws the man in (so to speak). The same thing happened when men were asked to evaluate a picture of a woman at two different times: when she was ovulating and when she wasn’t4. Again ovulation drew the men in; they rated the woman as more attractive when she was ovulating. No sense of smell was involved.
One possible difference was pupil dilation. An ovulating woman’s pupils are likelier to be more dilated, and this is rated as more attractive. Pupil dilation is also a sign of sexual arousal. Tiny pinprick (so to speak) pupils are unattractive. Another feature of the ovulating woman is that she tends to expose more skin. The researchers got the women to take pictures of themselves over a number of days and then calculated how much skin was exposed. There was a clear correlation with more skin being exposed during ovulation. This was probably triggered by a slight increase in body temperature, but it could also be due to the woman’s hormonal state, giving her more sexual confidence5.
Again, men found women with more skin exposed more attractive. Men also rate women dressed in red as more attractive than those dressed in other colours6. For the same reason, bright red lipstick or rouge makes a woman’s face more attractive. This is thought to be because a woman’s body tends to become red/pink during sexual arousal and so the red clothing is interpreted by the man as the woman being turned on. It has also been shown that women are more likely to wear red when they are ovulating. Finally, a woman’s voice is rated as more seductive when she is ovulating. Men are therefore pawns in a biological game whose mission it is to get a particular sperm to fertilise an egg, bringing the DNA of both people together to create new life.
What about the other way around? What attracts a woman to a man? Again, smell seems to play a crucial role. In one study, women were asked to smell men’s sweaty vests, and there was a correlation with the smell being rated as pleasant and how symmetrical the man was7. Appropriately, the lead scientist on that particular study was called Randy Thornhill. Attempts have been made to identify the chemicals involved, and products of testosterone called androstenone, androstadioenone and androstenol are good candidates, although the evidence that if a man sprays this stuff on himself it makes him attractive is patchy at best. The mix of chemicals involved is important, as is the context in which they are being smelled by the woman. Perhaps they work best in a candlelit restaurant with Barry White playing in the background.
VITRUVIAN MAN, A DRAWING FROM C. 1490 BY LEONARDO DA VINCI, BASED ON THE IDEAL HUMAN PROPORTIONS AS DESCRIBED BY THE ANCIENT ROMAN ARCHITECT VITRUVIUS.
Several studies have shown that we find symmetry attractive. A beautiful face is one that is symmetrical. This sends a signal that the person has good genes – they didn’t develop in an asymmetrical fashion, and therefore have robust bodies. This is good for attracting a mate who will have the best genes to pass on to your offspring. A lot of work has been done on symmetry. Women partnered to men with symmetrical bodies tend to have more orgasms8, and women with symmetrical breasts are more fertile9. This may reflect normal and balanced oestrogen levels, which also promotes ovary function.
Apart from symmetry, another physical trait that was found to be linked to attractiveness in men was the length of the ring finger10. Women notice its length, probably subconsciously. Men, pay attention. A woman may not be looking at your ring finger to see if you’re married. The length of the ring finger gives a strong indication of how much testosterone the man was exposed to in the womb. The longer it is relative to the index finger, the more testosterone was present. High levels of testosterone are linked to sperm count and increased fertility. However, women be warned. Men with long ring fingers are inclined to be more unfaithful, again most likely because of testosterone promoting an increase in libido.
The level of testosterone turns out to be a key difference between men and women, obvious as it may seem. It might give rise to slightly different brain structures, although that is controversial11. Whether a man’s brain is hard-wired to be physically different from a woman’s is a matter for debate. A large brain-imaging study recently carried out on this question found some differences, although there were more similarities than differences. There were 2,750 women and 2,466 men studied, and 68 regions within the brain were examined. A part of the brain called the cortex was thicker in women. A thicker cortex has been linked to higher scores in general intelligence tests. Men, however, on average had a larger hippocampus (the part of the brain involved in memory and spatial awareness), striatum (learning and reward processing) and thalamus (relaying sensory information to other parts of the brain). Men had a greater range of cortex sizes, which is consistent with men showing more variation in IQ tests than women. The study, although intriguing, doesn’t resolve the controversy as to whether these differences mean anything in terms of the behaviour or intelligence of men compared to women.
We do know that men and women behave differently; throughout the animal kingdom males are more aggressive and men are inclined on average to have better spatial reasoning. Women tend on average to be more empathic and caring. This could be due to testosterone levels. The environmental influence on the development of men and women, however, can’t be underestimated. One fascinating study showed that male babies elicit richer milk from a mother than female babies12. This could have all kinds of consequences for development, leading to male and female differences because of differences in nutrition.
Testosterone levels can vary widely in women, however, and this has become a bone of contention in sport. Some sportswomen have very high levels of testosterone naturally, and have better muscle mass and endurance as a result. The International Association of Athletics Federations is considering banning such women, but this is controversial. A well-known example is Caster Semenya, who won gold in the 800 metres in the 2012 and 2016 Olympics. She was subjected to gender tests that showed she had testosterone levels three times higher than average, and was ordered to take hormone-lowering drugs. But did we ban Usain Bolt because of his unnaturally springy legs? The problem is that there will always be athletes who have physiologies that place them in the top range, be it oxygen uptake or ability to tolerate high levels of lactic acid in their muscles.
Many studies have shown that women are attracted to more testosterone-driven, masculine-looking men, with above-average height, broad shoulders and a strong jaw all being rated highly. Women aren’t necessarily choosing virile men, however. Not all women prefer masculine men, and it again seems to depend on where she is in her cycle13. One study found that when a woman is ovulating, she is more drawn to masculine men, but interestingly only if her partner is not masculine-looking. One interpretation of this study is that she will want her egg fertilised by a masculine man, but then wants a less masculine man (who will possibly be more caring) the rest of the time, as he might be a better father to the child and less inclined to stray. This, however, is pure speculation.
TESTOSTERONE, THE PRIMARY MALE SEX HORMONE. IT PLAYS A KEY ROLE IN THE DEVELOPMENT OF MALE REPRODUCTIVE TISSUES AND PROMOTES SECONDARY SEXUAL CHARACTERISTICS SUCH AS INCREASED MUSCLE MASS AND BODY HAIR.
One fascinating aspect is that a man’s smell tells a woman something about his major histocompatibility (MHC) genes14. His what? Well, these genes play a key role in your immune system. Women prefer a man whose MHC genes are different from hers because the children will have a more varied MHC, which means they will be better able to fight infection. It’s like the MHC is a set of weapons. Variety is the spice of life. The more you have the more likely it is that you will kill an invader. However, it has also been shown that when a woman is using the contraceptive pill things change radically15. She prefers a less masculine man, and also a man whose MHC is more similar to her own.
This is because the contraceptive pill makes her body think that she’s pregnant, and so she is more drawn to a caring partner, which in the case of the MHC means a relative who is more likely to look after her off spring, as they will be related by blood. Another interesting finding with regard to the pill concerned sexual satisfaction. If a woman chose her mate while on the pill, she reports greater satisfaction with her partner as long as she stays on the pill. It’s as if the pill has changed her perception of her partner in some way, perhaps by enhancing her sense of smell for the pheromones he exudes. If she comes off the pill, perhaps that smell is no longer attractive.
One other trait that comes up as attractive, at least for some women, and perhaps only when she is ovulating, is risk-taking behaviour16. Activities such as smoking were seen as sexually attractive, as they signalled strength. If my body can stand this, I must have good genes. Death-defying activities like skydiving or Formula One racing are attractive because they appear to advertise strength and bravery. So does confidence in either sex – but not overconfidence. Musicians are deemed attractive because they show bravery and confidence in standing up to play music. So are sportsmen and women. Part of this involves being admired by others, which indicates alpha status and possibly good genes. To be overconfident, however, suggests perhaps that you’re hiding something, or that you’re a narcissist.
The good news is we are not just crude machines programmed to scan someone’s body, smell them and then go for it. Personality (as every Rose of Tralee knows) counts too. Certain personality traits play a role. Kindness has been shown to make someone more attractive17. People were asked to rate the attractiveness of photographs of faces. Two weeks later they were asked to evaluate them again, but this time some were labelled as ‘kind’ or ‘honest’. And guess what? Those so labelled were more likely to be rated as attractive than they were the first time around.
What makes all these studies so difficult is that each of us seems to have individual preferences. Some prefer small feet, some prefer a business suit, some prefer bald men. There are some universal qualities that the majority of us rate highly, though: a clear complexion, shiny hair, cleanliness, as well as a female waist/hip ratio of 7:10 and a male waist/hip ratio of 9:1018. These seem to be universal across all cultures, and are seen as signs of health, youth and good genes. But again, personality traits can dominate. There really does seem to be someone for everyone.
So once you’ve chosen your partner, what happens next? Again, multiple studies have shown clear chemical involvement, in this case hormones19. The early phase is characterised by testosterone and oestrogen. These trigger sexual desire. Testosterone is also made in women, and, as in men, will stimulate sexual desire. Oestrogen can have a similar effect, although it’s weaker. Women report increased desire when they are ovulating, which is likely to be due to oestrogen.
THE CHEMISTRY OF LOVE. IT STARTS WITH PHEROMONES WHICH DRIVE ATTRACTION. IN YOUR BRAIN, DIFFERENT NEUROTRANSMITTERS THEN KICK IN, CAUSING DESIRE, MAKING US FALL IN LOVE AND KEEPING US TOGETHER.
Once attraction kicks in, neurotransmitters in the brain play a role, with dopamine, noradrenalin and serotonin all getting involved. They provoke reward sensations. They also make us lose our appetite and cause insomnia. A famous song from the 1980s – ‘Addicted to Love’ – had it right: ‘You can’t eat. You can’t sleep. There’s no doubt, you’re in deep … Might as well face it, you’re addicted to love.’ We effectively become addicted to the person. This is why we spend hours looking at their Facebook page or hang around in the rain to see them, or wait desperately for a text message, or are compelled to go home via their street. They are like heroin, and in fact addictive drugs like heroin mimic the effect of falling in love. They share that same intensity and behavioural change, where all we want is that other person, just as all a heroin addict wants is more heroin. Imaging studies of the brain of people in love have shown that the reward centre in the brain (the caudate nucleus) lights up like a beacon in people who are shown a photo of the one they are in love with. The exact same region lights up when a heroin addict is shown heroin20. Lou Reed got it right when he sang ‘It’s such a perfect day, I’m glad I spent it with you’, which was actually about heroin and being in love with someone.
The involvement of serotonin is also no surprise. This is the neurotransmitter that causes obsessive-compulsive disorder, so again we see the link to total infatuation. All of these responses eventually wax and wane, the infatuation phase usually lasting from one to six months. They have to. Otherwise we would go nuts, and not do anything else all day other than gaze into the other person’s eyes, or make decisions that will prove to be harmful in the long run. Evolution had to make sure this would stop, as otherwise we would be eaten by a sabre-toothed tiger.
The last phase is attachment, and that is driven by two more hormones: oxytocin and vasopressin. Oxytocin is especially important21. It is sometimes called the ‘cuddle’ or love hormone. Our bodies make it when we’re forming attachments, meaning we bond to the person who is triggering it. We also produce it after orgasm, and nursing mothers make it in abundance to bond them to their babies. When a baby sucks on its mother’s breast, the stimulation triggers oxytocin’s production, in a marvellous example of a feed-forward loop. The suckling infant gets the mother’s body to make a hormone that bonds the mother to the baby, so that the baby can get more milk. You can buy oxytocin spray which the manufacturers claim will make the person you are beside bond with you. Or develop a sudden thirst for milk.
VOLES HAVE BEEN STUDIED TO HELP US UNDERSTAND THE BASIS OF MONOGAMY AND POLYGAMY IN MAMMALS. HUMANS ARE CLASSIFIED AS MILDLY POLYGAMOUS.
Oxytocin also brings us to the topic of fidelity. What makes us stay with the person we’ve chosen? Psychologists classify humans as being ‘mildly polygamous’. Most stay faithful but some stray, and there can be many reasons for this. The best scientific study carried out on polygamy and monogamy in animals involves the vole. These small furry creatures have been studied for decades for their behaviour, after it was noticed that two very closely related species (so related in fact that you can’t tell them apart by sight) had wildly different behaviours. The prairie vole, which, as the name suggests, lives on the open prairie, is monogamous, choosing a life partner and apparently never straying. The meadow vole, on the other hand, which lives in more lush grasslands, is a love rat. Meadow voles are polygamous. Scientists examined their DNA and found a striking difference. The genes that make the proteins that sense oxytocin and vasopressin (which is similar to oxytocin) are slightly different. In the monogamous prairie vole the genes become modified after sex, such that the level of the protein they make rises. The monogamous vole is therefore more strongly activated by vasopressin and oxytocin, because there are more of the sensor proteins in their brains.
OXYTOCIN: THE LOVE HORMONE.
So the theory goes that the prairie vole will keep seeking out the mate that triggered this pathway for the first time, as they will want the same ‘bang for their buck’, so to speak. It’s like they have heard one particular song during sex and then want to hear it again and again to produce the same feeling. Strikingly, the researchers were able to boost the levels of these sensors promoting monogamy22. This would suggest that you can dial monogamy up and down by regulating the levels of proteins in your brain. The higher their levels, the more likely you will stay true.
Some scientists are of the view that alcohol suppresses this pathway. This may in part explain why people who are drunk might cheat – it’s their vasopressin/oxytocin receptor protein being modified by alcohol that made them do it. Try telling your boyfriend that if he finds out. It also turns out that ‘beer goggles’ are real, especially for women drinkers23. We find people more attractive when we are drunk. We also find ourselves more attractive, which is the ultimate vanity. This can of course backfire badly, as we tell a prospective partner how great we are and think we are doing a great job of chatting them up.
Perhaps one way to test whether your relationship might survive is to test for the type of vasopressin or oxytocin receptor in your prospective partner. Another gene to test for is the serotonin transporter gene. Remember, serotonin is the happy neurotransmitter. It also makes us obsessively in love. It’s made in the brain where it regulates mood, anxiety and happiness. Illicit mood-altering drugs such as ecstasy cause a significant rise in serotonin in the brain. Serotonin is multifunctional, though, as it is also made in the gastrointestinal tract, where it regulates bowel movements; it also promotes such things as blood clotting and bone density. The serotonin transporter (which removes serotonin from fluids in your body) comes in two flavours: a long and a short form. If you have the short form, you are more likely to report marital dissatisfaction over time than if you have the long form24. The researchers had more than 150 adults in the study and assessed them over a 13-year period. In the lab they watched how they spoke to each other, examined facial expressions, topics of discussion and tone of voice. From these assessments they could tell if the marriage was a satisfying one or not. The things scientists get up to …
What might the future hold? Well perhaps one day lots of traits and genetic markers will be put into an algorithm and the program will find your perfect partner. There will be a more elaborate form of online matchmaking. And you will be helped in your goal if you spray yourself with Love Potion No. 9. Surely it’s more fun to find a mate in the wild, though? Do you believe in love at first sight? Yes, I’m certain it depends on testosterone, the serotonin transporter gene, ovulation and a 7:10 waist/hip ratio.