‘Tis the season for cheesy cards, overpriced restaurant dinners, flowers, chocolates, jewelry, and stuffed animals. I’ll admit that I’ve never been a huge fan of Valentine’s Day. We started off on the wrong foot, with those awkward grade-school valentine exchanges, and I’ve never seen eye-to-eye with Valentine’s day over the crass-consumerism that seems part-and-parcel with this holiday. That, and even in my most desperate days I could never understood the gustatory appeal of candy hearts.
This year, instead of doing my best to ignore the day, I thought I’d have a little fun. I’ve said it before and I’ll say it again: evolution is everywhere. This is never more true than in the bedroom!
Snuggling, cuddling, spooning… name your term.
Why do humans like to cuddle? There are a number of arguments that can be made for snuggling. Physical contact in the form of massage increases levels of the “love” hormone oxytocin  and decreases cortisol  (though some of the data on massage is fuzzy, perhaps because massage, especially in a research setting, can be a rather impersonal experience in comparison to cuddling). More frequent hugs increase oxytocin levels and lead to lower blood pressure and heart rate in premenopausal women . An interventional trial that looked at the effects of “warm touch” (including hand-holding, hugs, and “cuddling up”) in married couples showed an increase in salivary oxytocin (in husbands and wives) and a decrease in systolic BP (in husbands only) in the treatment group .
Increased oxytocin seems to enhance the effects of social support on stress responses . Oxytocin also plays a role in the early stages of romantic attachment, and encourages pair-bonding (and parental attachment) . But oxytocin isn’t the only compound that is altered by cuddling-up or that affects the way we feel about other people. There is also evidence that touch alters the release of endorphins, and that neuropeptides may play a role in the beneficial nature of physical touch .
On a day like Valentine’s Day, which purports to revolve around the concept of love (and chocolate sales), the arguments that physical contact reduces stress and increases the hormone associated with pair-bonding are probably king. Recently (and I did warn you I’m a bit cynical about this holiday), I’ve been wondering if there is something a little more… “anatomically practical” about cuddling.
Why you (men) shouldn’t “hit it and quit it”.
Anyone that has spent anytime thinking about human pair bonding has spent time thinking about short-term vs. long-term interests when it comes to the mating game. Yes, humans are predisposed to long-term bonding, but that doesn’t mean that there isn’t a significant role of short-term mating in human procreation (perhaps not as much now, thanks to social norms and the potential for paternity tests, but sources frequently cite that ~10% of children aren’t actually the offspring of the father that raises them, though a more thorough investigation shows that the rate is probably closer to 3% .). As an aside, while on my EMS elective I was repeatedly subjected to the Maury Povich show and it’s ilk while hanging out at headquarters (the lounge TV was usually blaring in the background). I doubt that Frederick Sanger imagined how his great discovery of DNA sequencing would be used when he developed the method in 1975 (for which he later won a Nobel prize in Chemistry- his second). “You are NOT the father!!!” But I digress…
Different species have various ways of decreasing paternity uncertainty. Some animals- canines for example- have a very… awkward (maybe I’m being anthropomorphic, I apologize) way of increasing the likelihood of paternity. After the completion of mating, the male doesn’t leave the female’s side. He can’t. Seriously. He is physically attached.
Dog mating is significantly different from that of humans. When the dog’s penis is first inserted into the vagina it isn’t actually erect and is only able to penetrate thanks to the penis bone, also known as the baculum. After insertion, the penis swells and the bulbus glandis at the base of the penis literally locks the penis in place, preventing the removal of the penis. This is known as “knotting” or “tying”. This cumbersome position usually lasts 5-20 minutes after ejaculation.
At least one book on dog genetics says that this process seems “quite irrational”, but the authors submit that it “must serve a purpose as it has remained despite apparent drawbacks, such as vulnerability to attacks during the act.” . I doubt I’m the first to suggest that the advantage of this prolonged intimacy is an increase in certainty of paternity. It seems rather obvious that this method of copulation gives the lucky suitor’s sperm time to gain advantage in the race to fertilization, before another competitor’s sperm can enter the race.
Fortunately, humans have not evolved this mechanism of assuring paternity. Instead, I’d argue that post-coital snuggling can offer some of the advantages of canine-coupling.
Some people might think that humans are above such an animalistic tendency. If a man doesn’t stick around long enough to ensure that his sperm have time to reach their destination, would another man’s actually get the chance?
Well maybe… It has actually been argued that the human penis is evolutionarily shaped (literally) to help a man get his semen where it needs to be, even if it didn’t actually get there first. In the article “The human penis as a semen displacement device*”, researchers argue that the shape of the human penis is “designed” to remove semen from the vagina during sex, clearing the way for new semen to be deposited in the most advantageous location (increasing the likelihood of paternity) . This strengthens the argument that if you’re a man, and you want to ensure paternity, it’s probably best you hang around to make sure your sperm doesn’t have any competition in reaching it’s goal.
So there you have it, the “principle into practice evolutionary argument for snuggling”. Sure, in the modern world men may not WANT paternity with every sexual encounter, but that doesn’t mean that the evolutionary mechanisms and behavioral predispositions aren’t already in place to improve paternity-certainty. On a day like Valentine’s day, you might rather focus on how cuddling increases oxytocin, leading to emotional bonding. Just remember that snuggling also physically bonds you, and that may not be such a bad thing…
*This paper wins the award for most giggle-worthy methods. Some of the lines could be right at home at #overlyhonestmethods. E.g.: “… this recipe was judged by three sexually experienced males to best approximate the viscosity and texture of human seminal fluid.”
1. Morhenn, V., L.E. Beavin, and P.J. Zak, Massage increases oxytocin and reduces adrenocorticotropin hormone in humans. Altern Ther Health Med, 2012. 18(6): p. 11-8.
2. Rapaport, M.H., P. Schettler, and C. Bresee, A preliminary study of the effects of repeated massage on hypothalamic-pituitary-adrenal and immune function in healthy individuals: a study of mechanisms of action and dosage. J Altern Complement Med, 2012. 18(8): p. 789-97.
3. Light, K.C., K.M. Grewen, and J.A. Amico, More frequent partner hugs and higher oxytocin levels are linked to lower blood pressure and heart rate in premenopausal women. Biol Psychol, 2005. 69(1): p. 5-21.
4. Holt-Lunstad, J., W.A. Birmingham, and K.C. Light, Influence of a “warm touch” support enhancement intervention among married couples on ambulatory blood pressure, oxytocin, alpha amylase, and cortisol. Psychosom Med, 2008. 70(9): p. 976-85.
5. Heinrichs, M., T. Baumgartner, C. Kirschbaum, and U. Ehlert, Social support and oxytocin interact to suppress cortisol and subjective responses to psychosocial stress. Biol Psychiatry, 2003. 54(12): p. 1389-98.
6. Schneiderman, I., O. Zagoory-Sharon, J.F. Leckman, and R. Feldman, Oxytocin during the initial stages of romantic attachment: relations to couples’ interactive reciprocity. Psychoneuroendocrinology, 2012. 37(8): p. 1277-85.
7. Keverne, E.B., N.D. Martensz, and B. Tuite, Beta-endorphin concentrations in cerebrospinal fluid of monkeys are influenced by grooming relationships. Psychoneuroendocrinology, 1989. 14(1-2): p. 155-61.
8. Dunbar, R.I., The social role of touch in humans and primates: behavioural function and neurobiological mechanisms. Neurosci Biobehav Rev, 2010. 34(2): p. 260-8.
9. Anderson, K.G., How Well Does Paternity Confidence Match Actual Paternity. Current Anthropology, 2006. 47(3): p. 513-520.
10. Ruvinsky, A. and J. Sampson, The Genetics of the Dog.
ed. 2001: Google Books.
11. Gallup, G.G., R.L. Burch, M.L. Zappieri, R.A. Parvez, M.L. Stockwell, and J.A. Davis, The human penis as a semen displacement device. Evolution and Human Behavior, 2003. 24: p. 277-289.