The time has come again for the annual celebration of love, Valentine’s Day – a day of romance on which many choose to express their affections to their loved ones. Many consider love as a complex network of emotions, expressing it in songs and poetry, but the question remains: What is the science behind falling in love?

Fortunately, scientists have a few explanations to define the feeling of love, and just as the English poet, Elizabeth Barrett Browning once said: “How do I love thee? Let me count the ways.”

The chemistry behind Cupid’s magic


Many say that chemistry is a key component of love – and the statement is not actually untrue. According to Helen Fisher, a Biological Anthropologist from Rutgers University in New Jersey, mammals exhibit emotions of love for the purpose of mating and reproduction, and is divided into three stages – namely lust, attraction, and attachment – each of which are mediated by hormones and chemicals in the brain.

The first stage, lust, is driven by testosterone and oestrogen, which lead to the craving for sexual consummation and is distinct from attraction or attachment.

“Women with higher levels of circulating testosterone have more sexual thoughts, greater desire for sex, and higher mean levels of sexual activity,” Fisher wrote, citing previous studies, adding that many women also report increased sexual desire just before ovulation – when oestrogen levels are at its peak.

Attraction, however, is mediated by monoamine neurotransmitters, such as dopamine, which is a likely agent for sleeplessness and reduced appetite observed in humans who are love-struck, as well as norepinephrine, which leads to heightened energy and exhilaration – properties of romantic attraction.

The third stage, attachment, unites individuals in a relationship and is distinct from that of sexual drive and attention, and is described as “the affection we feel for those with whom our lives are deeply entwined”. The hypothesis that attachment is distinct from sexual attraction, according to Fisher, explains why some spouses in arranged marriages maintain attachment to their partners and shared parental duties, without display of sexual desire for one another.

Attachment behaviours such as mother-infant bonding as well as feelings of security, peace and comfort are mediated by oxytocin, which is released by the hypothalamus when breast-feeding, holding hands or hugging, and contributes to stronger social bonds between mammals.

Love may lie within the gut

Hormones may sound like the most reasonable explanations to the science of love, but researchers have also found another factor that influences the complex emotion – gut microbes.

According to Susan Erdman, a microbiologist at the Massachusetts Institute of Technology, microbes that are found in the digestive tract may contribute to what she calls the “glow of health.”

After feeding mice with probiotic microbe that was isolated from human breast milk, it was observed that mammals grew more lustrous fur, inadvertently making them more physically attractive. The male rodents also had elevated testosterone levels while the females had higher levels of interleukin 10 and oxytocin – the same hormones that mediate feelings of love.

But microbes in the gut are not the only important microorganisms according to evolutionary biologists, who have long posited that the constant shuffle and exchange in virus helps maintain diversity in mankind and keeps us all alive.

“People tend to think of diseases, like the flu virus, spreading through social networks,” said Elizabeth Archie, a biologist at Notre Dame. “But a lot of the microbes you have are potentially useful. So maybe good things as well as bad things are spreading through the same modes.”

Kissing, for example, causes individuals to exchange viruses, which may, in some instances, lead to transmission of infections. However, this also allows women to acquire immunity against potentially dangerous infections before pregnancy – somewhat like a form of vaccination. Newborns are also exposed to microbes from mothers during birth, and carbohydrates from breast milk are important in maintaining the healthy microbial environment in the digestive tract.

The composition of other individual’s microbes can also influence one’s choices in partners, such as the attraction to body odour – a result of fermentation by microbes.

From neurotransmitter and hormones, to microorganisms – love truly is a complex emotion that is difficult to comprehend. But with scientists working hard to unravel the science behind love, we may soon demystify its mystery once and for all. MIMS

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