Unlike most other members of the animal kingdom, humans don�t have defined mating seasons.
Other animals typically mate during the time of year that maximizes the survival of their offspring. Many mammals that live in temperate climates will mate in the fall so that their offspring are born in the spring, when it is warmer and food is more plentiful[1].
Poetically, at least, human romance is also associated with the changing of the seasons�the harsh cold of winter brings the end of relationships, but the fresh promise of springtime invites feelings of love. Is there any merit to this notion?
An analysis of Facebook status updates provides some clues[2]. Researchers looked at the months with the highest net gains for romance�that is, where more relationships began than ended.
As it turns out, late winter to early spring (February through April) show big gains in romance. But fall months (September through November) do as well. The real low point for love is May through August.
These trends, which hold across all age groups, are shown in the chart below.
(Gorham & Fiore, 2012)
This same dataset even pinpoints the exact dates with the biggest gains in new relationships.
Apparently, major holidays are popular for pairing up. The four dates with the biggest increase in relationships were Valentine�s Day, Christmas Day, Christmas Eve, and February 15th (the day after Valentine�s).
A couple caveats: Not all Facebook users report their relationship status accurately. And many people fail to update their status on the exact date that their relationship begins or ends.
If new love peaks in the fall and early spring, what about sexual activity?
People are a bit more guarded about that on Facebook, but a study of Google searches is revealing[3].
By tracking keyword searches related to pornography, prostitution, and mate-seeking over the course of 5 years, researchers found that searches increased the most during early summer and winter months[3].
This suggests that interest in sexual activity spikes twice a year, but is silent on whether people actually engage in more sexual behavior at those times. It could be, for instance, that pornography is used as a substitute for partnered sex during the winter months.
But other data exist that get at sexual behavior more directly, and they tell the same story. Condom sales and sexually transmitted infections both peak in early summer and winter months. And births peak 9 months later[3].
To recap: Romantic relationships peak twice a year, in the early spring and fall. Sexual interest and activity also peak twice a year, about a month or two after the relationship peaks.
Why is this?
It could be simply that relationships beget sex, albeit with a slight delay. Or it may be that people have more time for sex in the winter and early summer.
One thing�s for sure: It�s hard to argue that having sex more often at these times is adaptive, in the sense of leading to healthier offspring. Mating in December means giving birth in September�just in time for colder temperatures and less food.
For the time being, then, why human mating behavior goes in cycles remains a mystery.
?References
1. Bronson, F.H. (2009). Climate change and seasonal reproduction in mammals. Philosophical Transactions of the Royal Society B: Biological Sciences, 364, 3331-3340.
2. Gorham, J., & Fiore, A.T. (2012, March 21). The right time for love: Tracking the seasonality of relationship formation. Retrieved from Facebook Data Science.
3. Markey, P.M., & Markey, C.N. (2013). Seasonal variation in internet keyword searches: A proxy assessment of sex mating behaviors. Archives of Sexual Behavior, 42, 515-521.
