“I had good argument for kissing once” –Shakespeare, Troilus and Cressida
With Valentine’s Day this week, thoughts turn to romance: flowers, chocolate, perhaps getting close with that special someone—looking forward to a goodnight kiss. In discussing V-day and this post with a friend, we pondered what it is about kissing that makes it sometimes so magical, when if you think about the mechanics of the act, it’s sort of disgusting. That said, there are those that claim there is an evolutionary explanation to our passion for puckering up.
In the last few years there have been many popular science writers who cite a 2010 publication in the journal Medical Hypotheses by Hendrie and Brewer to make the punch line for their articles that kissing is good for your health. When taking a closer look at this publication, I realized that these writers were making a bit of a leap with that assertion possibly to romanticize the science, or woo readers, or something.
So what does the journal article actually say?
Hendrie and Brewer are more specific about benefits the act of kissing may confer. Kissing can expose individuals who engage in the behavior to considerable disease risk associated with the introduction of foreign organisms. Hendrie and Brewer argue that the evolutionary benefit gained from kissing must be of great significance in order to warrant this type of risk. They propose that kissing behaviors arose in order to protect offspring from the teratogenic (causing abnormal development, usually birth defects) effects of human cytomegalovirus (HMCV).
HMCV, say what?
HMCV is one of the Herpes family of viruses and is pervasive in humans. Hendrie and Brewer consider infection with HMCV inevitable, we may all have it and never even know since the severity of symptoms varies widely and then the infection subsides and goes dormant in the body. The point of particular concern is the timing of when primary infection occurs. Should a woman first become infected during pregnancy, there are serious adverse impacts on the offspring (those teratogenic effects!) including mental retardation, cerebral palsy, diseases of various organ systems, and even death. Where in the spectrum of outcomes depends upon when in the pregnancy infection occurs—with the more severe outcomes resulting from first trimester infections (Kumar & Prokay).
To avoid those horrible consequences, evolution has selected for… KISSING!
So, how does that work?
The idea is that since HMCV is present in saliva, the exchange in saliva as during kissing can expose a woman to small amounts of the virus over time prior to when she might become pregnant. Hence our typical courtship behaviors (i.e. getting to “first base” at least a few times before you hit a “homerun”). This way, by the time a sexual liaison occurs there has been ample salivary exchange to expose the woman to HMCV such that any potential offspring will not be subject to adverse health outcomes.
Sounds great in theory…
However, I have yet to find any mechanistic studies that prove HMCV is actually exchanged during kissing. Perhaps researchers have more pressing topics to explore—I understand. So when those science writer are using this one study to make broader claims, it gives me pause to consider the facts and try to dig deeper.
What did I find? And what does it mean for you?
Since the implied benefit of this evolutionary adaptation is for potential offspring, what does this mean in the present, for the kisser and the kissee? Well, in her book, The Science of Kissing, Sheril Kirshenbaum, a research scientist at the University of Texas at Austin explores other potential biological impacts of kissing. She suggests that kissing is associated with changes in the levels of the hormone oxytocin, which is connected with romantic bonding behaviors. She also explains that women become sexually stimulated by small amounts of a man’s testosterone transmitted in his saliva—why kissing makes for good foreplay. In yet another study, by Floyd et al., kissing was found to decrease perceived stress, increase relationship satisfaction, and even improve total cholesterol.
So it turns out that kissing IS likely both good for future generations and perhaps for your individual health. It’s also likely that people are going engage in kissing whether or not it is good for them. But isn’t it nice when something we enjoy may actually be to our benefit? In that light, I know what I’m doing on Valentine’s Day!
Floyd K., Boren J.P., Hannawa A.F., Hesse C., McEwan B., & Veksler A.E. (2009). Kissing in marital and cohabiting relationships: Effects on blood lipids, stress, and relationship satisfaction. Western Journal of Communication, 73(2):113-133. doi: 10.1080/10570310902856071.
Hendrie, C.A., Brewer, G. (2010). Kissing as an evolutionary adaptation to protect against Human Cytomegalovirus-like teratogenesis. Medical Hypotheses, 74: 222-224. doi:10.1016/j.mehy.2009.09.033.
Kirshenbaum, S. (2011). The science of kissing: What our lips are telling us. New York, NY: Grand Central Publishing.
Kumar M.L., Prokay S.L. (1983). Experimental primary cytomegalovirus infection in pregnancy: timing and fetal outcome. Am J Obstet Gynecol, 145(1):56-60.