Science of Love and Sex

So Valentine’s Day came and went. Did you snuggle up to your other half and celebrate?
Many have tried to define what love is through song, poetry or even philosophical musings, but what of the science of it? There is a lot to say about what happens once we partner off in two just like the animals for Noah’s Ark. If you are wondering what goes on, then here is your handy guide!

Towards monogamy
One aspect of human sexuality has evolved according to different levels of investment in offspring and the energy in producing sex cells. As Jared Diamond explains in his book Why is sex fun? as men produce large amounts of their sex cells with less energy than women the inclination is towards promiscuity to impregnate as many women as possible. Women however invest a lot of energy into only one egg at a time, so to make it worthwhile they seek a partner that will provide and share in child-rearing. The so-called “battle of the sexes” within the lineage that led to humans describes the evolutionary response between males and females to retain their promiscuity and monogamy respectively. For instance, as humans, we females have developed concealed ovulation, not revealing when we are at our most fertile. This means that if a man wants to ensure that a woman gives birth to his children, he has to remain by her side thus reinforcing the idea of pairing up and staying that way.

Did your eyes meet across a room? Or were you introduced to each other through friends? Either way, the question remains: is the feeling of attraction a mutual one?
It is the signals of health and genetic fitness that we find ourselves attracted to. For women, the hourglass figure indicates good fertility and increased likelihood of infant survivability. Wearing red has been shown to increase male attention. It appears it may be an evolutionary hangover from when females display their red genitalia to indicate ovulation, which occurs in non-human primate species. For men, they need to indicate they have good parenting skills. It is probably a good idea to have an intermediate level of beardedness, as it has been found that women find men with beards much more attractive and better skilled at parenting. For both genders, it has been found that symmetry plays a significant role in being attractive- just make sure you see their whole face.

Now it is time to get up and close as testosterone courses through the veins of both men and women increasing the lust factor, even though women have considerably less. If you are feeling nervous that is the adrenaline making you a little sweaty and your heart race. It is probably a good idea to get a good sniff of the other person if you want children with them. Particular genes of the immune system known as the major histocompability complex affect an individual’s scent. If someone smells good to you, then that means your genes and theirs will provide your children with strong immunity.

Dating and Infatuation
By now you are seeing each other quite frequently and have had a saucy (but safe) night in. However even in your time apart you can’t help but think about them constantly, maybe even a little obsessively. Perhaps as a result of it you have texted them proclaiming how much you want to see them immediately. That is the result of dopamine and serotonin released into your brain. Dopamine plays a role in motivation and addiction as part of the reward system. As more is released to create a “kick”, the more it is sought. Low serotonin is linked to increased sexual desire and compulsiveness. Combined, these hormones ensure that you want to get together with your beau.

Bonds are strengthened by the oxytocin and the vasopressin as the infatuation hormones calm down. Oxytocin, known as the love-hormone, is released during intimacy, cuddling, sex, kissing and provides the happy feeling when you know you are in love. The more it is released, the deeper the bond with your partner. Moreover in men it has been shown to decrease the likelihood of him straying from his partner thereby reinforcing monogamy. With vasopressin, both hormones have been shown to indicate a high quality relationship and as an added benefit reduces stress and aids in wound healing. Apart from providing some physical benefits, a study has also revealed that idealising your partner to only see their positives actually serves as a feedback loop to ensure that we change to better ourselves. So as it turns out, we improve along the way.

It seems that there may be a biological basis for the 7 year itch, or rather as Helen Fisher writes in the Scientific American, the 4 year itch. 7 years is the median duration of a marriage, but 4 is the mode. It turns out amongst humans divorce occurs mostly during the reproductive years. In an attempt to understand this, Fisher conducted a study looking at birds and mammals. It appears that in birds pair bonding occurs only long enough to rear the young to toddlerhood. Fisher suggests that we may have inherited an aspect of this, that 4 years is long enough to raise a child with our partner until other support systems can step in and help out. In the New Scientist, she explains what happens when we are rejected by loved ones, and it is down to dopamine. As we expect the reward from dopamine to occur after being dumped, it does not and strangely enough it actually increases the love we feel for the one who has rejected us. As the stress system kicks in, adrenaline and serotonin can then lead to depression. But it appears this depression is the down-time that is needed, as one theory posits it allows someone to collate social support which ultimately allows us to bounce back.

We are not reduced to our biology!
Despite the scientific evolutionary studies conducted, it turns out that social and economic factors have a much bigger role than we realise, as is outlined by the New Scientist: For one thing, women’s independence has meant that looking for a man to provide is not necessarily the case. Not all women place high earning potential as a top-priority in seeking a partner. Women’s independence has also increased their desire for promiscuity and conversely, some men may have done a cost/benefit calculation in their heads and realised that casual sex is no longer for them. Additionally, where food scarce, it is more attractive for a woman to have a larger waist rather than an hourglass figure.

It appears the general picture of love and sex has been formed by evolution but coloured by social and economic factors that can vary geographically, by culture and by generation. Nevertheless, love no matter how it is defined is crucial to the continuation of our species. Without it we would not be here, which I liken to what Oscar Wilde (1854-1900) once said:
“Keep love in your heart. A life without it is like a sunless garden when the flowers are dead.”

Danae Dodge

I received my PhD in Scientific Archaeology from the University of Sheffield in 2011 which specialised in ancient DNA and anthropology. For my profile, see my websites: I started getting involved in Science Brainwaves as a volunteer in 2010. I have volunteered at presentations, events (such as the British Science Festival in 2011) and even participated in the Science is Vital protest march in October 2010. My first blog for Science Brainwaves was "Ancient Humans: Who were they? And who got it on?" which was the written version of a talk I gave for the Natural History Society at the University of Sheffield on 5 December 2011. I also have a public engagement page dedicated to ancient DNA, which I encourage both the public and specialists to join: