Major religious holidays seem to spark a wave of sexual desire around the world, with a boom in online interest in sex and a spike in babies born nine months later.

Research published in the journal Scientific Reports has for the first time taken a “planetary-level” look at the phenomenon in Christian countries, which leads to a spike in births in September - nine months after Christmas.

The study found the same pattern following the Muslim festival of Eid-Al-Fitr.

Scientists have previously hypothesised this increase could have an evolutionary root, timing reproduction to the changing of the seasons.

However, the study found the phenomenon seems to be culturally driven and occurs around the world.

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It found the September birth spike is still apparent in Southern Hemisphere Christian countries, even though Christmas falls in their summer.

“We didn't see a reversal in birth rate or online interest in sex trends between the Northern and Southern hemispheres,” said Luis Rocha, a professor in the Indiana University School of Informatics, Computing and Engineering, who co-led the study.

“It didn't seem to matter how far people lived from the equator.

“Rather, the study found culture - measured through online mood - to be the primary driver behind cyclic sexual and reproductive behaviour in human populations."

In Muslim-majority countries there was also an increase in birth rates nine months after the Eid-Al-Fitr celebration, which marks the end of the fasting-period of Ramadan and falls at different times each year.

The researchers have also used a new method to explore people's feeling during the festive period.

Analysing Twitter messages from seven countries - Argentina, Australia, Brazil, Chile, Indonesia, Turkey and the USA, researchers assigned them a “sentiment” score from one to nine.

The paper notes that generic holiday greetings would be discounted, but says: “For example, the word 'laughter' has a score of 8.5, while 'leprosy' has a score of 2.1.”

This sentiment score was also combined with the number of sex-related Google searches in the country in the weeks before, during and after its major religious holidays.

This found that as well as an increase in sex-interest, all these countries tended to be happier at these times.

The report says: “It is very counter-intuitive to think of Christmas and Eid as the times of the year with the most online searches for sex.

“However, these events may trigger specific and collective moods, leading to a striking correspondence between these holidays and sexual interest.”

It also found other holidays, like Easter and Thanksgiving, did not produce the same spike.

The report concludes: “Our analyses provide strong converging evidence for the cultural hypothesis: human reproductive cycles are driven by culture rather than biological adaptation to seasonal cycles.

“Furthermore, the observed peaks of interest in sex occur around family-oriented religious holidays, across different hemispheres and cultures, and the measured collective mood on these holidays correlates with interest in sex throughout the year, beyond these holidays.”

Professor Rocha said this new insight could help target public health campaigns in the future and said that strong results “are likely to hold true in developing nations" where data wasn’t available.