While you’re in bed, why not find someone to help keep it warm? Conveniently enough, the region of the brain that stimulates the release of sex hormones, the hypothalamus, is sensitive to light and circadian rhythms. In autumn, as daylight hours decrease, testosterone levels
—which are associated with libido—increase slightly. Around this time, says John Sharp, a Harvard neuropsychiatrist and author of The Emotional Calendar
, men and women start to date seriously, and as winter proceeds, the heat is on to find a long-term partner. Come December, Internet keyword searches related to sex and dating soar. This is when sales of Trojan condoms reach a peak, and so do conception rates. In the U.S., more babies are born nine months later, in September, than any other month of the year.