Human reproduction does not happen uniformly throughout the year and what drives human sexual cycles is a long-standing question. We found that interest in sex peaks sharply online during major cultural and religious celebrations, regardless of hemisphere location. This online interest, when shifted by nine months, corresponds to documented human births, even after adjusting for numerous factors such as language and amount of free time due to holidays.
We further showed that mood, measured independently on Twitter, contains distinct collective emotions associated with those cultural celebrations. Our results provided converging evidence that the cyclic sexual and reproductive behavior of human populations is mostly driven by culture and that this interest in sex is associated with specific emotions, characteristic of major cultural and religious celebrations.