For millennia, observant Jewish couples have followed the laws of taharat hamishpaha, or family purity, which include refraining from sex during a woman’s period, and for a full seven days after the woman is niddah.

And, according to a new study to be presented at the Second Annual Conference on Judaism and Evolution at the Schechter Institute of Jewish Studies on Sunday, those couples may be on to something.

Rick Goldberg, an independent scholar based in Austin, Texas, and Dr. Orit Barenholz of Hadassah oversaw a study, in which 19 religiously observant, married Jewish men provided saliva swabs twice a week for three months, so their testosterone levels could be monitored. All of the men are residents of Beit Shemesh, a city near Jerusalem, and all practice hilchot niddah – refraining from sex from the moment the wife begins menstruating until she has counted seven clean days from the end of the period and then immersed herself in the mikveh, or ritual bath.

The study found a marked increase in testosterone in the men around the date of their wives’ mikveh immersion, which is also the first day she can return to sexual activity with her husband. Due to the timing of the female cycle, this date is also closely linked to a woman’s point of ovulation, which means that these religious couples may have a higher chance of both fertility and sexual libido during the monthly window when they are sexually intimate.

According to Goldberg, the results of this study suggest hat rituals rooted in the Torah may confer significant biological advantages.

“Biologically speaking, the behaviors that are the most adaptive are the ones that give the people practicing those behaviors an advantage, and they end up leaving more descendants,” he said. “That’s not a moral judgment. It’s a quantitative judgment. You and I and everybody else are the products of ancestors who were successful at reproducing — otherwise we wouldn’t be here. But how you get to that point, how you figure out what is adaptive and what is not in terms of fertility — this is what we look at specifically.”

The prohibition against a man having sexual intercourse with his wife while she is menstruating appears first in Leviticus. She becomes niddah the moment she notices the very first drop of blood of her menstrual cycle. When her cycle completes, she must perform daily checks and ensure all bleeding has stopped. Modern rabbinical interpretation calls for women to count seven “clean” days from the moment when menstruation stops, and then visit the mikveh. Only then can she welcome her husband back into her bed.

Based on an average five-day menstrual cycle, this practice sends a woman to the mikveh about 12 days after the start of her period, which is often right when she is ovulating. Coupled with the higher testosterone levels seen in the men in Goldberg and Barenholz’s study, which means a higher sperm count and better sperm health, these factors appear designed to produce a situation ideal for fertility.

Evolutionarily, it seems, the ancient practice of hilchot niddah has practical applications for couples looking to conceive.

Positive pregnancy test (illustrative photo credit: CC BY-ND Johannes Jander/Flickr)

Positive pregnancy test (illustrative photo credit: CC BY-ND Johannes Jander/Flickr)

That doesn’t mean, Goldberg said, that the centuries of Jews who have embraced the laws of ritual family purity understood these practices as anything more than commandments.

“My guess is they performed traditional obligations because that’s what the Torah told them to do — so that’s what they did,” he said. “My job is to shine a biological light on those behaviors and see if some illumination can be made of it biologically.”

The data was meant to be observed only as a case study, as no general sample group of nonobservant men was studied in tandem to provide a level of comparison to the hormone levels.

Goldberg will even admit on Sunday, when he presents his findings, that other variables could be at play and that the data, at this point, need further study.

Nevertheless, earlier studies of testosterone levels of men in long-term relationships have shown what so many bachelors have long insisted: The longer and more stable a husband’s marriage, the lower his testosterone levels.

Single men have higher testosterone levels than their married counterparts, and those whose marriages were reported as happy and without conflict also have lower levels of the male hormone than their peers in rocky unions.

Two studies, one out of China and one from Canada, have shown that men who are fathers have lower testosterone than those who are childless. But while there have been many studies performed on the impact of marriage and family life on men’s testosterone levels, Goldberg believes his study is the first of its kind to look at practices that can manipulate those testosterone levels to aid procreation.

Whether or not the laws were written with a scientific benefit in mind, and whether or not Jews of yore knew they were boosting their chances of conception when they decided to follow them, the study indicates that there is evolutionary value behind the practice of hilchot niddah.

“Suppose the period of abstinence was when the wives were ovulating. Suppose everything was backwards in the Torah,” Goldberg says. “How long do you think the Jewish people would have lasted?”