In a new study published this month in the journal Archives of Sexual Behavior researchers tracked Google keyword searches in the United States for pornography, prostitution and dating sites between January 2006 and March 2011. Researchers wanted to gauge the real-time mood of the nation and found that online interest in the mating game peaked around Christmas and early summer.

This bi-annual cycle isn’t unheard of. A 2007 review of research on sexual activity in young people published in the journal Health Education found a six-month cycle for human sexual activity in the United States. Research on the so-called “holiday season effect” and the “summer vacation effect” has involved studying the outcomes of sex, such as births and sexually transmitted infections (STI) — events that occur weeks to months after doing the deed.