Heavy periods can make even daily tasks difficult. Getting up from a chair, for example, can be an ordeal for someone worried about the possibility of having stained the seat. Mothers with low iron levels tend to have babies with low birth weights and other health problems, so the effects of heavy menstruation trickle down through generations. And yet the uterus often goes unacknowledged, even by researchers who are exploring topics like tissue regeneration, to which the organ is clearly relevant, Brosens says. “It is almost unforgivable, in my view,” he adds.
Ask researchers why menstruation remains so enigmatic and you’ll get a variety of answers. Most everyone agrees there’s not enough funding to attract the number of researchers the field deserves—as is often the case for health problems that primarily affect women. The fact that menstruation is shrouded in taboos doesn’t help. But some researchers say it has been hard to find the right tools to study the phenomenon.
Scientists tend to start studies of the human body in other organisms, such as mice, fruit flies, and yeast, before translating the knowledge back to humans. These so-called “model systems” reproduce quickly and can be altered genetically, and scientists can work with them without running into as many ethical or logistical concerns as they would if they experimented on people. But because menstruation is so rare in the animal kingdom, it’s been tough to find ways to study the process outside the human body. “I think that the main limitations are model systems, honestly,” says Julie Kim, a reproductive biologist at Northwestern University.
In the 1940s, the Dutch zoologist Cornelius Jan van der Horst was among the first scientists to work on an animal model for studying menstruation. Van der Horst was fascinated by unusual, poorly studied critters, and this fascination led him to South Africa, where he trapped and studied the elephant shrew. With a long snout reminiscent of an elephant’s trunk and a body similar to an opossum’s, the elephant shrew was already an oddball when van der Horst learned that it’s one of the few animals that get a period—a fact he probably discovered “more or less by accident,” says Anthony Carter, a developmental biologist at the University of Southern Denmark who wrote a review of van der Horst’s work.
Elephant shrews are not cooperative study subjects, however. They only menstruate at certain times of year, and they don’t do well in captivity. There’s also the challenge of catching them, which van der Horst and his colleagues attempted with hand-held nets. The shrews were agile, so it was “sometimes a fascinating but mostly a disappointing sport,” he wrote.
Around the same time, George W.D. Hamlett, a Harvard-based biologist, discovered an alternative. Hamlett was examining preserved samples of a nectar-loving bat called Glossophaga soricina when he noticed evidence of menstruation. The bats, which live primarily in Central and South America, were not easily accessible, so for several decades his discovery remained simply a point of interest in the scientific literature.
Then, in the 1960s, an eager graduate student named John J. Rasweiler IV enrolled at Cornell University. Rasweiler wanted to study a type of animal reproduction that mirrors what happens in humans, so his mentor pointed out Hamlett’s discovery. Perhaps Rasweiler would like to go find some bats and see what he could do with them?
With a long snout reminiscent of an elephant’s trunk and a body similar to an opossum’s, the elephant shrew was already an oddball when van der Horst learned that it’s one of the few animals that get a period.
“It was a very challenging undertaking,” Rasweiler says. “Essentially I had to invent everything from start to finish.” First there were the trips to Trinidad and Colombia to collect the bats. Then there was the issue of how to transport them back to the United States without their getting crushed or overheating. (Shipping them in takeout food containers, bundled together into a larger package, turned out to work well.) Once the bats were in the lab, he had to figure out how to work with them without letting them escape. He ended up constructing a walk-in cage on wheels that he could roll up to the bats’ enclosures.