Growing up in Ireland, in an earlier generation, a person's chance of being sexually active outside marriage was low. Even the use of contraception was illegal.

Irish people looked to England as a godless center of carnal delight. At the same time, young men raised in drab old England sought sexual adventure by traveling south, to Spain, or north, to Sweden. It is always greener on the other side of the hill.

Can science help us to determine which countries are less inhibited in sexual matters? Can we take the guesswork out of sexual tourism? Or will airlines continue to profit from the misguided excursions of uninformed travelers?

Sex researchers devised a questionnaire that measures how interested people are in sex without commitment. This asks about a person's number of sex partners and their attitudes toward casual sex. Information is available for 48 countries (1). Unfortunately, Ireland and Sweden are not included.

Countries scoring close to the top are something of a surprise. They are not the United Kingdom (above average), or Spain (below average), or even France (around average), but Finland and New Zealand (1). Why are the Finns so amorous? Why are the French so lukewarm? Incidentally, the U.S. is also around average. Countries with the least interest in casual sex are located in Asia and they include Taiwan and Bangladesh.

Intrigued by the great variety of attitudes to uncommitted sexual relationships, I wondered whether inhabitants of different countries are influenced by the various risks of sexual behavior for them (2).

Casual sex can be dangerous or costly for multiple reasons. In prudish societies, just one slip can ruin a young woman's marriage prospects and even precipitate her death at the hands of irate relatives. It can be equally dangerous for men. I found that casual sex was disapproved of in nations where there is a relative scarcity of women. Such societies are very focused on marriage and expect young women to reserve sex until after their nuptials. Conversely, where there are more women than men, women find it difficult to marry and are more likely to be sexually active outside marriage (3).

Apart from ruining a person's marriage prospects, casual sex carries the risk of life-threatening illnesses. Sleeping around is consequently unpopular in countries where there is a high incidence of HIV/AIDS.

Wealthy countries are widely assumed to be more sexually liberated but this expectation was confirmed only in relation to women's interest in sex. Men's interest in casual sex actually declines in wealthy nations. It seems that in countries where women actively pursue sex outside marriage men may value sexual interactions less or take less interest in fleeting relationships.

One completely unexpected discovery was that the biggest influence on sexual motivation is population density. Being close to a lot of sexually attractive people does not pique interest in casual sex but actually inhibits it. This could be because crowding is stressful and stress hormones reduce interest in sex. It is also possible that having a lot of people around reduces an individual's sense of privacy.

Taiwan and Bangladesh are very different in many ways but both are densely populated countries. That helps account for their relative lack of interest in casual sex. Finland is a very sparsely populated country whereas France has seven times as many inhabitants per square mile, helping to explain why the Finns are hotter than the French. The population density of New Zealand is about the same as Finland.

Sexual tourism advisory: stay away from the densely-populated countries of Asia. Cancel that trip to Paris in the spring. Head for Helsinki. Cultivate a Kiwi. Good luck!

1. Schmitt, D. P. (2004). Sociosexuality from Argentina to Zimbabwe. Behavioral and Brain Sciences, 28, 215-311.
2. Barber, N. (2008). Cross-national variation in the motivation for uncommitted sex: The role of disease and social risks. Evolutionary Psychology, 6, 217-228.
3. Guttentag, M., & Secord, P. F. (1983). Too many women: The sex ratio question. Beverly Hills, CA: Sage. Barber, N. (2002). The science of romance. Buffalo, NY: Prometheus.

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