Why More Babies Get Made During the Holidays


Dec 26, 2017


Scientists at the Instituto Gulbenkian de Ciencia, Portugal, and Indiana University, USA, have found there is a specific mood associated with religious celebrations, a “loving mood” that can influence human reproductive behaviour. The research team, led by Joana Goncalves-Sa and Luis Rocha, used worldwide data from Twitter and Google Trends to find that culture, and not only biology, drives human reproductive cycles.

In other words, everyone is having holiday sex, regardless of culture or creed.

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 (the month of Christmas) 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 merely a theory.

“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,” said Goncalves-Sa. “However, nowadays everybody uses the Internet and social media, regardless of location or culture. This phenomenon can provide useful data for research.”

The team tracked people’s mood and online behaviour throughout the year, in different countries across 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 holiday tradition but not necessarily among countries that share geographical location — countries like Australia or Brazil had patterns similar to Northern hemisphere countries like Portugal, Germany or the USA. On the other hand, Turkey or Egypt’s patterns differed from other countries in the Northern hemisphere, but the online behaviour of its citizens was 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,” Rocha said. “Since these celebrations fall on the same date in both Northern and Southern Hemispheres, cultural traditions and not geography, must be driving these moods.”

In Christian countries the “love mood” is higher around Christmas holiday, as 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,” Goncalves-Sa said. “Christmas and Eid-al-Fitr are family-oriented religious holidays that generate specific happier and calmer mood states that probably drive interest in sex.”

A wink and a nod to all the mums expecting babies in late July 2018 — we know what you did last Diwali. (Because everyone else was doing it, too.)



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Written By Lila Sahija

Lila reports on health and science news for The Swaddle. She has loved biology ever since she dissected her first frog in eighth grade, and now has a keen interest in examining human behavior. She also loves animals and takes at least one adventure a year through rural India. Oh, and she bakes a mean German coffee cake.


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