There is no moment more universally recognized as symbolic of renewal than the coming of spring. Previously shackled by cold air and short days, men and women are finally freed from the confines of their homes and offices to lounge in the sun, travel, and fill up the outdoor leisure spaces of the world. In almost every culture on the planet, spring is seen as a time of growth and rebirth. Flowers bloom. Animals emerge from their winter refuges. Homes, towns, and cities begin to buzz with activity. After a cold, dark slumber, life returns.
Springtime, in turn, is often associated with an upswing in romance. “In the spring a livelier iris changes on the burnished dove,” goes “Locksley Hall,” one of Alfred Lord Tennyson’s more recognizable poems. “In the spring a young man's fancy lightly turns to thoughts of love.” And in the spring, just as plants wake from their winter dormancy, so too does a carnal desire—or so we’re told. As the warmer weather arrives, we pursue romance, flirt more, and are more prone to sexual encounters.
But what impact, if any, do seasonal changes really have on romance? Do higher temperatures and longer days get us all hot and bothered?
While scientists report that human reproduction is far less seasonally dictated than that of other creatures, birth rates do rise and fall in distinct patterns throughout the year.
That the changing of the seasons directly affects our disposition is not a new concept. It was a core part of Enlightenment thinkers like Adam Ferguson's calculus when considering the laws of war and peace in the world of nation-states, a major factor in determining which nations were “rude” and barbarous and which were “polished” and civilized (although the scientific connection between high temperatures and bad tempers has been hotly contested). In the U.S., various institutions like the public school system are built on the vestiges of a pre-industrial America bound to the harvest. And on a more personal scale, the National Institute for Health says six percent of the U.S. population, primarily in northern climates, are affected by seasonal affective disorder (SAD) “in its most marked form,” while another 14 percent suffers from a lesser form of seasonal mood changes known as “winter blues.” The ebb and flow of the year shapes the nature of commerce, government, and international relations in subtle—yet powerful—ways.
Springtime really is for lovers, according to the research. A comprehensive and much-cited study in a 1990 issue of The Journal of Reproductive Rhythms suggests that human fertility rates are directly influenced by seasonal changes, and that sunlight and temperature are two outstanding factors in shaping procreation. While scientists report that human reproduction is far less seasonally dictated than that of other creatures, birth rates do rise and fall in distinct patterns throughout the year.
The perfect time of year to conceive, according to this analysis, is when the sun shines for about 12 hours and the temperature hovers between 50 and 70 degrees Fahrenheit. “For reasons that remain mysterious,” the New York Times wrote at the time of the report’s first publication, “such conditions somehow help stimulate either ovulation in women, a burst of sperm production in men or a combination of the two.” (More recent research has suggested that the lowest testosterone levels for men actually occurred during those months with the highest temperatures and longest hours of daylight.) Where you live matters, of course: The research notes that geographical discrepancies in the data reflect where certain places were exposed to the ideal mix of daylight and temperature for conception.
Conscious coupling isn’t a purely biological impulse, though, and more recent research explores the social layer that connects seasons and intimacy. In a 2002 study in the Journal of Marriage and Family, researchers Martin Levin, Xiaohe Xu, and John Bartkowski used the National Longitudinal Study of Adolescent Health to define two seasonal peaks in the onset of sexual and romantic activity among adolescents, one in the early summertime months and another during December, or “the holiday season effect.” By looking at partner relationship context (romantic vs. non-romantic) on each peak, the authors found that summertime activity typically occurs between non-romantic partners, and wintertime activity between romantic partners with a pre-existing history. This research finds an easy parallel in our current society: Most American college students would probably agree that winter is an appropriate time to lock down a mate to share a warm bed with. No point in trudging across campus in the snow for every sexual encounter.
There are psychological factors, of course. A 2008 study in Perception by Bogusław Pawlowski and Piotr Sorokowski suggests that men’s attraction to women’s bodies changes as the seasons do. The researchers asked a group of 114 Polish men to judge the attractiveness of photographs of women's faces, breasts, and bodies, at three-month intervals, between the winters of 2004 and 2005. The subjects found images of women’s bodies and breasts (but not faces) more attractive when tested during winter than summer. The researchers theorized that this result may be due to habituation to the surplus of exposed skin touted by women during the warmer months.
This research may seem to suggest that we’re more easily aroused in the winter because of the scarce glimpses of human flesh, but there’s another interesting consequence: As we become used to encountering romantic prospects hidden under a mass of boots, sweaters, and coats during the dead of winter, we become habituated to overlook those physical features that trigger arousal. The transition from winter to spring and summer, as temperatures gradually rise, can yield new romantic prospects as men and women begin to take in what had previously gone unnoticed. Consider it a seasonal version of the Baader-Meinhof phenomenon: You catch Susan in her new sundress or Paul in a tank top at your local park and pretty soon you’re noticing their curves or muscles far more often.
Perhaps the answer is purely cultural. Most Americans likely associated hot weather with hot behavior: lad-and-gal mags like Cosmopolitan and Men’s Health have built entire audiences on the idea of encouraging naughty, summer fun on their covers. That’s probably not without cause: According to 2012 research by Matthew Vess of Ohio University on embodied cognition—that the nature of the human mind is largely shaped by the sensory experiences of the body—human beings are disposed to associate temperature with their emotional perceptions of other people and their relationships in an “unconscious mingling of the personal and the thermal,” as Kai MacDonald of Scientific American summarized. Since the concept of warmth is generally associated with intimacy (and “passion,” as Adam Ferguson would say), even moderate heat, after months of cold, is enough to induce people to be more friendly, outgoing, and social—a change in behavior that could lead to, as Slate’s J Bryan Lowder put it, “all kinds of other connections.”
So do hot temperatures make people burn with desire? Biology, climate, and geography all shape our basic impulses, but when it comes to your day-to-day courtship during the heat of the summer, your sense of romance may just be all in your head.