Few animal species reproduce with male pregnancy with examples including seahorses and some fish. Until recently, there were no records of male mammals giving birth.
The phenomenon was not natural – male rats were surgically prepared to nurture a embryos in a transplanted uterus. The project yielded a low 4% success rate, but the male rats delivered pups that grew without any reported complication. While some have excitedly associated the experiment’s success with the possibility of human application, the lead researcher has repeatedly pleaded online to not implicate the study with potential male human pregnancy. Regardless of such prospects, this paper has gained tremendous attention for its ethical ramifications.
The experiment was inspired when a researcher read about parabiosis, a surgical procedure used to fuse the circulatory system of two animals so that they share their blood. A procedure was then created reasoning that male mammals cannot maintain a pregnancy because they are lacking a uterus and the appropriate molecules in their blood to support embryo growth. The study, not yet peer reviewed, reveals the procedure as the follows:
- Castrate the male rats (to lower testosterone) and stitch them to a female rat (creating heterosexual parabiotic pairs).
- Transplant a grafted uterus to the male rat.
- Transfer embryos to the uteruses of both rats.
- Delivered pups by caesarean section.
The procedure and the results triggered an avalanche of tweets questioning its ethics. Scientists debated whether the scientific progress justified the invasiveness of the procedure. One even raised concerns on whether this study is indicative of science turning into an entertainment business. The lead researcher responded by reassuring that, “[the] animals did not have any painful symptoms such as screaming during the entire experiment” and asked that people “… please don’t bring non-scientific factors into scientific research.”
Apart from the success of “pregnant” male rats, the paper highlights that their male pregnancies were only successful when attached to a pregnant female and that the male mice sometimes carried abnormal fetuses. Neither of these findings were unexpected.
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I pitched this to Massive Science and it was published after the piece was made much more neutral. But there’s a lot I wanted to convey in this recent Massive Science articles that I couldn’t include, namely that these experiments scared researchers too. The rats were made pregnant with a series of surgeries and only 4% of the embryos survived. They report no noticeable abnormalities in these live pups. The author conveys that this is an important contribution to reproductive research because no male mammals have carried a pregnancy before. They even loosely relate this to potential human application in the paper.
However, almost every researcher I’ve talked to about this paper has a major criticism; that the rat’s surgical procedures do not justify the experiment. The author wrote that their study confirmed that hormones in the pregnant female’s blood are required to carry a pregnancy and that males really only need a uterus to house the embryos. Other researchers rebuttal that these requirements have been known for decades.
Additionally, when people asked about the rats, the author responded publicly by saying that they weren’t screaming throughout the experiment, an experiment that lasted weeks. Not mentioned by the experimenter is that there are other tests for assessing discomfort and pain in rats. The author also asked that people not talk about the study philosophically.
This study was done in a country infamous for having loose animal-rights regulations. Most other countries on the forefront of science have strict regulations for approving experiments that utilize animals which would have prohibited this study. And so this study horrified scientists and animal-rights activists alike.
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