Love? It’s in the genes

The science of attraction by Sean Duke, editor of Science SPIN Magazine ([email protected]


Picture the scene.

You are at a party, chatting casually to friends. Then, out of the corner of your eye, you become aware of a presence. Your eyes are transfixed. You’re frozen in time. A celestial angel is in the room and begins to walk slowly towards you, moving ever closer and closer. The conversation with friends begins to fade into the background like a gentle murmur. Are you staring? You avert your eyes in a vain attempt to avoid detection. Help. Your heartbeat starts to race, your palms begin to sweat, and your face is flushed red. It must be love. But, what exactly is that? According to scientists it is a bio-chemical response to a range of smells, sights and sounds, which are hitting the senses like a sledgehammer. The scientists believe we are more slaves to our senses, and to subconscious signals when choosing a partner than we would like to admit. Free will, in love, it seems, is vastly overrated.

When morality is stripped away from sex what do we find? Biology can help explain much of our sexual behaviour, but how much are we simply prisoners of our most basic instincts? Is there a thing called love? Or is it just a chemical reaction in the brain that is necessary to allow couples to have sex? Do we pick a partner of free will? Or are we governed by our subtle senses and subconscious mind?
In Oregon, one study found that the male partner of the parental pair did not sire 10 per cent of the children surveyed in the study. It appears that if love exists at all, many people don’t practice it.

A woman makes an enormous physiological investment in producing eggs. She has only a limited number of eggs, and a relatively short number of fertile years. So, for the woman’s genes to survive to the next generation – which biologists such as Charles Darwin would argue is at the root of sexual behaviour – it is vital that she the right man to fertilise her eggs. That man should be of different genetic make-up so that her children will be provided with additional valuable genes. The man also must be able to protect and fed her, and her children. For the woman, the goal is to find “Mr. Right.”

For men, it’s different. They put little physiological investment into individual sperm, and millions of sperm are being produced in the testes all the time. In addition, in biological terms, the best way for the male to ensure that his genes survive into the next generation is to copulate with as many women as possible. For the man, finding the right woman might mean having to suppress his most basic instincts.


We have all heard people saying “they have great chemistry”, or “there is no chemistry between them.” Well, these statements might carry more weight than most of us might have thought. A number of chemicals play a key role in the game of love, in humans, other animals, and plants. One of the most basic impulses in mankind, is that of lust, and the hormones that drive this primeval force of attraction are the female oestrogen hormone, and the male testosterone hormone. Males and females posses both hormones, and the relative levels in each person vary. But, there are lots of other important chemicals that are key to this story. There are a number of so-called ‘neuro-transmitting’ chemicals that trigger responses in the brain. The most important of these in sexual chemistry are dopamine, norepinephrine (more commonly known as adrenaline) and serotonin. Low levels of dopamine and serotonin in the brain can lead to serious depression, and even suicide, while high levels – such as occurs when a person is attracted to another person – leads to feeling of well-being or even elation. Adrenaline, meanwhile, the so-called “flight or fight” hormone, cause the heart to race, and the pores to sweat.

As all couples are aware, the initial surge of attraction that accompanies meeting the person of your dreams, is followed by a settling down period, where couples may decide to move in together, get married, buy a house, or have children. During this phase of their relationship, a couple that are well suited chemically will remain attracted to each other, but other chemicals now come into play, namely, oxytocin, and vasopressin. The oxytocin chemical, or hormone (a chemical produced by the body that performs a job of work), is linked with child birth, and facilitates the production of milk in the mother after the birth. Both partners also release this chemical during sexual intercourse, and, scientists believe that it, thus, plays an important role in ensuring the couple remain bonded. Meanwhile, vasopressin is thought to have a role in ensuring each person protects the other from new suitors.


There evidence now emerging indicates that all of us are drawn to the smells, and body chemistry, of those that resemble our parents. Girls are drawn to men that have similar chemistry to their father, and boys are draw to women that resemble their mother. It appears, in evolutionary terms, that this strategy is to avoid in-breeding, which can produce birth deformities, and also not to stray to far from a safe bet

Unless a person smells pretty awful, or is fabulously fragrant, most of us probably done consciously dwell too long on what a potential partner smells like. However, though our conscious mind might be apathetic when it comes to smell, the unconscious mind is working overtime. The reason for this is that we all transmit chemicals, called pheromones, into our immediate environment. These pheromones provide information about our chemistry, and, thus, our genetic makeup. It had been known for years that pheromones played a role in animal attraction: for example, it was known that rates were able to identify the sex of fellow rats and how resistant they are to disease via pheromones. However, then in 1985 at the University of Colorado it emerged that pheromones were also crucial for human attraction, when a group of pheromone-sensitive organs, called vomeronasal organs, were found in the nostrils. It was also found that these organs were linked to the brain region, which is responsible for the emotions.

There have been some remarkable experiments done with smell. For example, one simple study, which was aired on the BBC programme QED some years back, provided an example of the power of smell. A sample of male pheromones, from a sweat gland, was placed on a seat in a doctor’s surgery. All the prospective patients that visited the surgery were women. The researchers found that the woman all sat close, or directly next to the end of the room with the pheromone. In another famous study, conducted at Bern University, a group of women were presented with men’s sweaty T-shirts, and asked to rate them according to intensity of odour, pleasantness, and sexiness. The women picked up pheromone signals from the shirt and were, thus, able to distinguish men that had a different immune system to themselves. The women found the odour of men with different immune systems to be most appealing. The interpretation put on the findings was that women – at the subconscious level at least – are actively seeking out men with different genes, in order to provide, strong diverse genes for their future children.

This tendency for women to seek out genetically different males, was confirmed in another study conducted by researchers at the University of Chicago, into a small, socially isolated religious group, based in South Dakota, called the Hutterites. This tiny, close-knit group of people is descended from a mere 64 immigrants from Europe. They marry among themselves and have large families. So, everyone in the group has a similar genetic make-up. However, it was found – when DNA samples were taken – that there were less genetically similar couples that would have been expected by random choice. So, here again, even in this close-knit community, the women were seeking out genetically different males, and they did this subconsciously by picking up the male pheromone signals from the nostril glands.


We have all heard of the famous “hour glass figure”. It is a shape that men adore, and that women strive to have. But, there is a biological basis behind the reason why men like this shape. Studies have proved that the optimal waist-to-hip ratio, in terms of what men like in women, is 0.7. The hips are, thus, larger than the waste, but not too much larger. This specific ratio indicates fertility, as younger girls would not have it, as their hips haven’t developed, and older women tend to have fat on their waist. Interestingly, the 0.7 ratio remains the same across a range of weights. Another study found that it was also the average ratio of the girls that were taking part in a particular Miss USA beauty pageant.

Other research indicates that we are all narcissistic, in the sense that we are attracted to people that look like ourselves. This can explain why many couples look similar to each other. A study by cognitive psychologist, David Perrett, at the University of St. Andrews, found solid evidence for this assertion. The researcher used a computerised ‘morphing’ programme, to transform the sex of each face, so that the men become women, and women, men. The group were then asked to pick out the face that they liked most. Dr. Perrett discovered that the students were drawn most to their own ‘morphed’ image.


Unlike human societies, there is no pretence of monogamy in the animal kingdom where none exists. There is no hypocrisy to cloud the picture, and no sense of guilt, or peer pressure, which prevents individuals from expressing their own natural sexuality. Animals, are, very rarely, truly monogamous.

The most monogamous animals in the world, biologists have found, are the birds. In many bird species there are breeding pairs: a couple that share the same nest, raise their children together and fight off intruders. It has been found that more than 90 per cent of bird species are monogamous, which compares very favourably with the group that humans are a part of – the mammals – where only three per cent of species are monogamous. The situation is a little better for the primate sub-group, again which humans belong to, and here we find that 15 per cent of species are monogamous. In fact, monogamy is rarer, and develops only where females occupy a small space, and males dominate.

For those that believe in true love the depressing fact is that even the shining example of monogamy in the animal kingdom – the birds – are cheating on the side. The vast majority of birds are socially monogamous, meaning that they live together and raise their children together, but only 10 per cent are genetically monogamous, which means being faithful to one partner sexually. The situation is worse for other species, and among the monkeys, only the marmoset and the tamarin are sexually faithful.

Researchers at Cornell University have found, using genetic techniques, which even the most devoted of partners in the animal kingdom have been found to share the sexual company of complete strangers. However, an additional finding was that females that are socially bonded with what they perceive as high-quality mates do not copulate outside the pair bonds. They are apparently happy with their lot.

A relationship has been found between testes size and body size, which determines whether an animal will be promiscuous, polygynous or monogamous. Promiscuous is when an animal mates with many different mates, as many as possible, while polygynous means an animal mates with a number of females within a controlled ‘harem’ type environment. Chimps are promiscuous and gorillas are polygynous, for example, and this means the chimp has relatively larger testes. Applying the relative testes size to humans, means that they are placed in between monogamous and polygynous. This puts biological sense on the fact that some men play around, while others are happily married and at home.