There’s likely no one key reason for a particular orientation, research shows
enetics and random environmental factors each play a major role in determining both gay and heterosexual behavior, say British and Swedish researchers.

“This study puts cold water on any concerns that we are looking for a single ‘gay gene’ or a single environmental variable which could be used to ’select out’ homosexuality — the factors which influence sexual orientation are complex. And we are not simply talking about homosexuality here — heterosexual behavior is also influenced by a mixture of genetic and environmental factors,” study co-author Dr. Qazi Rahman, a leading scientist on human sexual orientation, said in a prepared statement.

Environmental factors are specific to an individual and may include biological processes such as different hormone exposure in the womb, the researchers noted.

The researchers studied more than 3,800 same-gender twin pairs, ages 20 to 47, in Sweden. The twins were asked about the total numbers of opposite sex and same sex partners they had ever had.

“Overall, genetics accounted for around 35 percent of the differences between men in homosexual behavior and other individual-specific environmental factors (that is, not societal attitudes, family or parenting which are shared be twins) accounted for around 64 percent. In other words, men become gay or straight because of different developmental pathways, not just one pathway,” Rahman said.

Among the female twins, genetics explained about 18 percent of the variation in sexual orientation, non-shared environmental factors 64 percent, and family environment 16 percent.

It’s important to note that heredity and shared environment had roughly the same influence in women, while shared environment had virtually no impact on men’s sexual behavior, the researchers said.

The study, which was published in the journal Archives of Sexual Behavior, shows that while genetic factors are important, non-shared environmental factors are dominant in determining sexual orientation.

“This study is not without its limitations — we used a behavioral measure of sexual orientation which might be okay to use for men (men’s psychological orientation, sexual behavior, and sexual responses are highly related) but less so for women (who show a clearer separation between these elements of sexuality),” Rahman noted. “Despite this, our study provides the most unbiased estimates presented so far of genetic and non-genetic contributions to sexual orientation.”

Study finds big jump in number of those over 70 who are intimate and enjoying it

When it comes to sex, grandma and grandpa are having more of it these days, new Swedish research suggests.

According to the study, the last quarter century has seen a dramatic rise in the frequency of sex among the 70-year-old set, whether married or unmarried. And as an added bonus, seniors today (particularly women) say they’re much more satisfied with their liaisons than the previous generation — facing less sexual dysfunction and feeling more positive about the experience.

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“Our study shows that a large majority of elderly consider sexual activity and sexual feelings a natural part of late life,” said study author Nils Beckman, a doctoral candidate with the neuropsychiatric epidemiology unit at the Institute of Neuroscience and Physiology at Gothenburg University. “It is thus important that health professionals and others take sexuality into consideration, irrespective of age.”

The findings are reported online in the British Medical Journal.

Beckman and his team reviewed surveys concerning sexual behavior and attitudes that had been completed by more than 1,500 healthy 70-year-old Gothenburg residents over a 30-year period.

Between the first survey and the last, the frequency of sexual intercourse was found to have increased among all groups. Among married men, 68 percent said they were engaging in the practice in the latest poll, compared with 52 percent in 1971, while among married women the number had risen from 38 percent to 56 percent.

Among unmarried men, the jump went from 30 percent to 54 percent in the same 30-year span, while among unmarried women the observed bump was from just under 1 percent to 12 percent.

Women seemed to make the most headway in terms of increasing their sexual satisfaction. While men expressed more positive attitudes about sex in 1971, by 2001 the gender difference had evaporated.

As well, more 21st-century women said they were highly satisfied with their sex; fewer said they had low satisfaction; more said they experienced an orgasm during sex; and fewer said they had never had an orgasm.

Regarding the degree to which the respondents said they felt “very happy” about their relationship, the three-decade trend also moved in a similarly positive direction for both genders: rising from 40 percent to 57 percent among men, and from 35 percent to 52 percent among women.

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Beckman and his colleagues speculated that, in part, the findings might simply reflect the degree to which Western societies have become more comfortable in dealing with sexual matters frankly and openly — perhaps leading to a greater willingness to honestly report sexual encounters.