Turning heads with a kiss
In this season of love and romance, you might find yourself wondering with whom you should spend Valentine’s Day. How will you celebrate the festive, yet ever so slightly commercialized holiday? And how and where do you execute the perfect kiss?
In the case of the latter, one burning question remains: Which way do you turn your head as you reach in for a kiss?
In 2003, psychologist Onur Güntürkün of Ruhr-Universität-Bochum observed 124 couples kissing in public areas such as airports, parks, and train stations in the United States, Turkey, and Germany. Twice as many couples tilted their heads to the right as opposed to the left.
A University of Amsterdam study, published by John van der Kamp and Rouwen Canal-Bruland last year, focuses on a more socially awkward possibility. What if one person prefers to lean to the right, while the other tilts their head to the left before their lips meet?
In particular, one issue with Güntürkün’s result was that an individual’s bias is not necessarily reflected in the direction of head-turning in a couple. Thus, the more recent study questioned whether right-turners were just as likely to adapt to a partner’s left-turning preferences, or vice versa.
Some 57 study participants were asked to kiss a life-sized doll’s head, with adjustable orientations to the left or right. The participant’s individual head-turning preference was found by orienting the head at zero degrees. This was followed up with another 35 kisses, in which the doll was rotated at different angles.
Participants tended to switch their direction when faced with an incompatible orientation. However, right-turners were found to be more persistent in maintaining their head-turning direction, even when the doll was made to kiss to the left. In other words, right-turners were more hesitant to adapt to the doll’s direction compared to left-turners. As a result, couples with opposite head-turning preferences will often turn to the right.
The authors reason that since right-turners are more prevalent in adulthood — this study showed 72 per cent of individuals were right-turning — left-turners may encounter incompatible orientations more frequently and thus face more pressures to switch sides.
Of course, results such as these have wider-reaching applications than human romance. Güntürkün has long questioned why humans are twice as likely to use the right foot, ear, or eye, than the left. He hypothesizes that this joint pattern of lateral bias starts when the fetus turns its head in the womb, and that newborn humans continue to exhibit this head-turning in the first three to six months of life. However, the Güntürkün study was the first to show that behavioural asymmetry continues long into adulthood.
It is worth noting that the kissing bias may have no correlation with the widespread propensity to use the right hand as opposed to the left. In fact, right-handedness is eight times more common. Instead, handedness is attributed to environmental factors such as social pressures on children to write with their right hand.
Güntürkün’s theory has been met with skepticism from fellow academics. Chris McManus of University College London points out that in order to prove Güntürkün’s hypothesis, it would be necessary to follow infants with known head-turning preferences across their lifespan, instead of simply observing couples with unknown backgrounds.
Daniel Geschwind of UCLA further states that there is no clear correspondence between head-turning and other asymmetries, which have their own respective influences by early patterning — for example, the fact that ear-sidedness is related to language.
Indeed, the University of Amsterdam study suggests that the kissing bias is independent of the aforementioned joint pattern of lateral preferences, contrary to Güntürkün’s claims. The study gathered handedness, footedness, and eye preferences, and showed that the direction of head-turning often contradicted hand and foot preferences, supporting the notion that perhaps the head, hand, foot, and eye have separate lateral specializations. The authors of the study recommend further research regarding the laterality of each of these functions.—Fiona Tran
The evolution of kissing
Researchers at the University of Leeds and the University of Lancashire have hypothesized that mouth-to-mouth kissing — specifically the kind that involves the exchange of saliva — is a behaviour that evolved in human beings in response to the threats posed by the Human Cytomegalovirus, or HCMV.
HCMV, an infection that is ubiquitous in human populations, is a form of the herpes virus that can have severe teratogenic effects — effects harmful to developing fetuses — if the mother is first infected while she is pregnant. HCMV is readily transferred from person to person through bodily fluids such as saliva, urine, and semen. Thus, as the scientists have proposed, women evolved in ways to become infected before conception.
The HCMV virus is a potent one, affecting approximately 8,000 children in the United States, even today. This is an especially staggering number when taking into account that pregnancies are normally terminated if the infection is detected. This disease can cause a fetal mortality rate of up to 30 per cent. Neonates that escape mortality are susceptible to disabilities like cerebral palsy, seizures, and motor disabilities.
Although mothers who are infected prior to conception still have a chance of transferring the disease to their babies in utero, this probability is decreased from 50 per cent if the mother is first infected while pregnant, to only 0.5–2.5 per cent if she is infected before conception. Thus primary infection before conception is highly advantageous.
Scientists Colin Hendrie and Gayle Brewer proposed an evolutionary explanation for avoiding infection from the HCMV virus, in a February 2010 article published in the journal Medical Hypotheses. The new theory states that, in order to avoid primary infection when pregnant, females have developed behavioural strategies to protect their child. Infection is inevitable during sexual intercourse, since the virus spreads through bodily fluids. Thus, making an attempt to become infected prior to conception is the only viable course of action.
The scientists propose that open-mouth kissing during courtship is just such an attempt, allowing women to expose themselves to the male’s particular strain of HCMV before sexual intercourse has begun. In such behaviours, saliva from the male carrying small amounts of the virus will flow into the typically shorter female, effectively inoculating the potential mother against further infection from that particular viral strain during pregnancy.
Explaining the origin of mouth-to-mouth kissing is an effort that other scientists have undertaken in the past. Other theories accounting for its evolution include attempts to look to behaviours exhibited by other members of the animal kingdom.
In many other animals, mouth-to-mouth contact can be used in fighting, or as a way of begging parents for food. One theory states that mouth-to-mouth kissing evolved from mouth-to-mouth contact between parents and children in their infancy, as a way to orally exchange food. This sort of premasticated food exchange is seen in isolated human populations in Papua New Guinea and the San of South-West Africa.
Hendrie and Brewer explain this behaviour by observing that these populations did not come into contact with HCMV until after the arrival of Europeans, effectively explaining the onset of sexual mouth-to-mouth kissing as an adaptation to the introduction of the virus.
Other hypotheses suggest that mouth-to-mouth kissing evolved to support pair-bonding between partners in order to care better for their offspring. This theory states that hormones released through the act of affectionate kissing, including such neuropeptides as oxytocin, results in a stronger bond. However, the release of these hormones arises from acts other than that of kissing as well, exonerating kissing as the only cause of stronger pair bonding.
Even today, we have not been able to develop any vaccines for HCMV. The evolution of behavioural strategies seems to be the best way to stop the infection of neonates. So go ahead and kiss your partner this Valentine’s Day. You may be doing more than just showing your love.—Pallavi Hariharan
