WEDNESDAY, May 6, 2015 (HealthDay News) -- Millennials aren't pairing off with as many sex partners as Baby Boomers and Gen Xers, but they're more accepting of premarital sex and same-sex relationships.
That's the conclusion of a new review that charted Americans' evolving views on sex, relationships and behavior.
"We found a really profound shift in sexual attitudes and behavior," said study lead author Jean Twenge, a professor of psychology at San Diego State University. "In the 1970s, it was much more common to say that sex before marriage was wrong or sometimes wrong. And it was by far the majority view to say sex between two adults of the same sex was wrong.
"That has changed a huge amount," she added.
Twenge and her colleagues launched their study to gain a better understanding of how generational attitudes about sex and sexuality have shifted over the past four decades.
The researchers looked at results of a national survey conducted most years between 1972 and 2012. Nearly 57,000 people took part in the survey, and the study authors said they adjusted the statistics to reflect the American population as a whole.
The researchers found that the sexual revolution of the 1960s made a huge difference in Americans' lives. People born in the first decades of the 20th century -- the so-called "Greatest Generation" -- had an average of 3 sex partners in a lifetime, while the "Silent Generation" -- those born in the 1930s and 1940s -- had 5 partners.
But things changed dramatically with the arrival of Baby Boomers in the late 1940s, 1950s and early '60s, who have averaged 12 sex partners. Generation Xers -- those born in the late '60s and '70s -- will average 10 sex partners, while Millennials -- those born in the '80s and '90s -- will average 8 partners. (The researchers said they extrapolated how many partners Gen Xers and Millennials would have over their lifetimes.)
"I was surprised that there was a little bit of a decrease," Twenge said. But, she added, "It has to be taken into context: 8 is still a lot higher than 3, and it's higher than 4. But yes, it's less than the Boomers."
HIV and other sexually transmitted diseases might play a role in the declining number of sex partners, Twenge said. So could the rise of the "friends with benefits" trend -- with many younger Americans having sex with a friend instead of going out and looking for more "hook-ups."
Overall, the percentage of people who said premarital sex is "not wrong at all" grew steadily over the years, from 29 percent in the early 1970s to 58 percent by 2012.
And the acceptance of same-sex sexual relations rose from 13 percent in 1990 to 44 percent in 2012. By the 2010-12 surveys, 56 percent of Millennials said same-sex pairings were OK. (The study authors noted that these surveys were conducted before many states approved the legality of same-sex marriage.)
The study also revealed a gender divide. "Women are more accepting of homosexuality," Twenge said. "Perhaps they see it as less threatening than men do. But they're more conservative about premarital sex."
Twenge said the big-picture message from the study points to a rise in individualism, with a "cultural system that places more on the needs of the self and less on social rules."
"You get more tolerance and acceptance: I'm going to do my thing and you can do your thing," she said.
The study was published in the May 5 issue of the journal Archives of Sexual Behavior.
To learn more about teen sexual behavior, visit the U.S. Department of Health and Human Services.