A sexy girl in Santa Suite
A sexy girl in Santa Suite

It has long been held that birth rates peak in September and studies in the past have suggested that the “baby boom” is the result of seasonal changes in human biology. New research however suggests that more than biology, it is the collective mood of a community or the social milieu that may create conditions conducive to a “baby boom”.

Scientists at Indiana University and the Instituto Gulbenkian de Ciência in Portugal used the “collective unconscious” of web searches and Twitter posts to establish that spikes in pregnancies really happen after celebrations – Christmas in Christian-majority countries and Eid-ul-Fitr, the celebration that marks the end of Ramzan, in Muslim-majority countries. The study, which appeared in the journal Scientific Reports draws upon data from nearly 130 countries that included sex-related Google search terms from 2004 to 2014 and 10 percent of public Twitter posts from late 2010 to early 2014.

“The rise of the web and social media provides the unprecedented power to analyze changes in people’s collective mood and behavior on a massive scale. This study is the first ‘planetary-level’ look at human reproduction as it relates to people’s moods and interest in sex online,” said Luis M Rocha, a professor in the IU School of Informatics, Computing and Engineering, who co-led the study.

The analysis revealed that interest in sex peaks significantly during major cultural or religious celebrations

The analysis revealed that interest in sex peaks significantly during major cultural or religious celebrations — based upon a greater use of the word “sex” or other sexual terms in web searches. These peaks broadly corresponded to an increase in births nine months later in countries with available birth-rate data. Moreover, the effect was observed in two different cultures, with the greatest spike occurring during major holiday celebrations.

A sexy girl in Santa Suite
A sexy girl in Santa Suite

The use of data from the Northern and Southern hemispheres is notable since past analyses tended to focus on smaller geographic areas in the Western and Northern hemispheres. The case of Eid-ul-Fitr is significant because the holiday does not occur on the same day each year, but the measured effect still shifts accordingly, following a clear cultural pattern.

Because the seasons are reversed on opposites sides of the globe, and peak birth rates and online interest in sex did not change based on geography, the researchers concluded the relationship between these effects is unrelated to biological shifts caused by changes in daylight, temperature or food availability.

“We didn’t see a reversal in birth rate or online interest in sex trends between the Northern and Southern hemispheres — and it didn’t seem to matter how far people lived from the equator,” Rocha said. “Rather, the study found culture — measured through online mood — to be the primary driver behind cyclic sexual and reproductive behavior in human populations.”

To understand the higher interest in sex during holidays, the researchers also conducted a sophisticated review of word choices in Twitter posts — known as a “sentiment analysis” — to reveal that, collectively, people appear to feel happier, safer and calmer during the holidays. When these collective moods appear on other occasions throughout the year, the analysis also found a corresponding increase in online interest in sex. Interestingly, Thanksgiving and Easter did not generate the same mood and online interest in sex.

“We observe that Christmas and Eid-ul-Fitr are characterized by distinct collective moods that correlate with increased fertility. Perhaps people feel a greater motivation to grow their families during holidays when the emphasis is on love and gift-giving to children. The Christmas season is also associated with stories about the baby Jesus and holy family, which may put people in a loving, happy, ‘family mood,” Rocha said.

The study’s results are notable for reasons beyond curiosity about the rise in babies born nine months after the holidays. For example, Rocha said the findings could help public health researchers pinpoint the best dates to launch public awareness campaigns encouraging safe sex in developing countries lacking in reliable birth-rate data.

“The strong correlation between birth rates and the holidays in countries where birth-rate data is available — regardless of hemisphere or the dominant religion — suggests these trends are also likely to hold true in developing nations,” he added.

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