This Week in Sex is a weekly summary of news and research related to sexual behavior, sexuality education, contraception, STIs, and more.

And Then There Were Four: More Porn Stars Test Positive for HIV

Porn sets are dark again as industry insiders collect information about what may be an outbreak of HIV among performers, and public health advocates say that enough is enough. As Rewire has been reporting, filming stopped in late August when a female star, who uses the stage name Cameron Bay, announced she had tested positive for the virus. The industry’s self-imposed moratorium was lifted when all of Bay’s on-screen partners tested negative. As the industry was recovering from this pause in filming, an actor whose screen name is Rod Daily announced on Twitter that he, too, had tested positive. Daily stars mainly in gay porn but has been romantically linked to Bay. His announcement did not cause a second moratorium on filming, however, because he was tested at a facility not linked to the industry. The Free Speech Coalition, the industry trade group that takes responsibility for testing actors, told the New York Times that it asked Daily to present his test results to them but he was not under any obligation to do so (presumably because he was not reporting to work).

In the week since Daily’s announcement, there have been two other confirmed cases of HIV in porn actors, both of whom opted not to be named. The Free Speech Coalition has halted production again. A spokeswoman for the organization said in a statement, “While we don’t have evidence to suggest an on-set transmission as opposed to a transmission from non-industry (off-camera) related activity, we are taking every measure to determine the source and to protect the performer pool.”

Michael Weinstein, president of the AIDS Healthcare Foundation, an advocacy group that has been pushing for mandatory condom use on all adult films, sees the outbreak as proof that the current system is not working regardless of whether any of these stars were infected on set. He told the Los Angeles Times, “Whether or not [Bay] was infected on set, she performed with HIV between her tests. If you think that Russian roulette is a great way to protect workers, then the present system is perfect.”

Weinstein hopes that this new outbreak will at least be a catalyst for change in the industry. “People thought it was a weird, quirky thing,” he told NPR, “and now I think they see it as a real health issue.”

Do Men With Smaller Balls Make Better Dads?

To add to our list of things that we can’t believe anyone thought to research, we now know that men who take a more active role in child care have smaller testicles. Yep, researchers at Emory University asked 70 heterosexual cohabiting couples with very young children to complete a questionnaire about how they divided up parenting jobs (like baths, doctor’s visits, and nighttime comforting) and gave the man a score based on how involved he was. They then measured each man’s testicles using MRIs and found a clear trend—as parenting scores rose, testes size fell. This correlation remained even after the researchers controlled for men’s height and testosterone levels.

Though these findings only show a correlation and do not explain the cause (are men with smaller testicles drawn to parenting activities or do parenting activities cause testicles to shrink?), the researchers believe that the results add to our understanding of evolutionary biology and something called life history theory. Essentially there are two ways that male animals can maximize their chances of having offspring who can continue their lineage—have a few children and invest heavily in their upbringing or spread your seed far and wide but do little to raise your kids. Chimpanzees do the former, sea turtles do the latter. The authors believe that their findings about males “are the strongest evidence yet that variations in male anatomy reflect competing evolutionary strategies.”

The study’s lead author, Jennifer Mascaro, told the Guardian, “We are not saying you can determine a man’s parenting aptitude based on their individual biology. But it does suggest that some men may be wired to participate in childcare more than others. They may take to it more readily.”

Estrogen, It’s Not Just for Women

We all know that estrogen is one of the main female sex hormones and that men make testosterone, but the truth is that both genders produce and need both hormones. And a new study published in the New England Journal of Medicine has found that male libido is actually dependent on estrogen.

Researchers enrolled 400 men between the ages of 20 and 50 and gave them treatments to suppress their bodies’ production of all reproductive hormones. Some men then received a placebo, another group got testosterone-boosting gel, and another group got testosterone-boosting gel and a drug that suppressed estrogen. They found that those men who were getting the estrogen-suppressing drug had a greater reduction of sexual desire than the other men in the study.

Joel Finkelstein, the study’s author, told Bloomberg News that many might find the results unexpected. “What will surprise many people is that loss of sexual desire in men with low testosterone is due to lack of estrogen,” said Finkelstein. “People think estrogen in men makes them very effeminate; they think of it as a female hormone, they think it is testosterone that gives men their sexual desire.” He went on to explain that these results should not change the treatment for men with low libidos who are often given replacement testosterone. The body is able to convert these treatments into estrogen so taking testosterone should also increase estrogen levels. That said, Finkelstein believes the results should “discourage drug makers from trying to develop new forms of testosterone replacements that aren’t able to be converted to estrogen.”