Scientists at the Instituto Gulbenkian de Ciência (IGC, Portugal) and Indiana University (IU, USA) showed that there is a specific mood associated with religious celebrations, and that this “loving mood” can influence human reproductive behaviour. The research team led by Joana Gonçalves-Sá and Luís Rocha used worldwide data from Twitter and Google Trends to find that culture, and not only biology, drives human reproductive cycles. This study is to be published in the open access journal Scientific Reports* on 21 December.

In Northern hemisphere Western countries, more babies are born in September than in other months of the year. This means that more babies are conceived in December and that human reproduction displays a cyclical pattern. Until now, it was mainly thought that the peak in conceptions was due to a biological adaptation to winter’s shorter days and low temperatures, since in Northern countries the winter solstice occurs in December. But lack of accurate worldwide data left this hypothesis untested.

“It is relatively easy to find accurate birth records in Northern Hemisphere, ‘western’ countries, but not for most other countries. This has biased the analysis towards a specific region and culture and limited our understanding of the world. However, nowadays everybody uses the Internet and social media, regardless of location or culture. This phenomenon can provide useful data for research”, explains IGC researcher Joana Gonçalves-Sá.

The research team set to track people’s mood and online behaviour throughout the year, in different countries, from both Northern and Southern Hemispheres, and with different cultural traditions (Christian or Muslim).
They found that online searches related to sex have a cyclical nature that correlates with a specific “loving mood”, as independently detected on Twitter. Moreover, they saw that these cyclical patterns are very similar among countries that share the same cultural tradition but not necessarily among countries that share geographical location. Countries like Australia or Brazil had similar patterns when compared to Northern hemisphere countries such as Portugal, Germany or the USA. On the other hand, Turkey or Egypt’s patterns differed from that of other countries in the Northern hemisphere, but had an online behaviour similar to the Southern hemispheric Muslim Indonesia.

“We demonstrated that worldwide peaks of sexual interest exist and coincide with specific religious celebrations, leading to peaks in birth rates 9 months later. Since these celebrations fall on the same date in both Northern and Southern Hemispheres, cultural traditions and not geography, must be driving these moods”, says Luís Rocha, researcher at the IGC and at Indiana University.

In Christian countries the “love mood” is higher around Christmas time and so are online searches related to sex, whereas in Muslim countries a similar behaviour happens around the religious festivities of Eid-al-Fitr and Eid-al-Adha.

“Our results suggest that human reproductive cycles depend on the collective mood of human societies. Christmas and Eid-al-Fitr are family-oriented religious holidays that generate specific happier and calmer mood states that probably drive interest in sex”, says Joana Gonçalves-Sá.

“This is an instance where data from social media and online searches allowed us to solve a question that for the longest time had been debated in biological circles. These new online ‘macroscopes’ allow us to look at society at a grander scale, and is changing completely the way we study human behaviour”, says Luís Rocha.

This study was conducted at Instituto Gulbenkian de Ciência (Portugal) and at Indiana University (USA), with the collaboration of Wageningen University (The Netherlands). This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia, the Marie Curie Actions and the USA National Institutes of Health.

*Wood, I.B., Varela, P. L., Bollen, J., Rocha, M.L., Gonçalves-Sá, J. (2017) Human Sexual Cycles are Driven by Culture and Match Collective Moods. Scientific Reports. DOI. 10.1038/s41598-017-18262-5.

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