But within 20 days of the transfer, the monkeys’ follicles stopped growing and looked different, Liu and colleagues said, publishing their results in the journal Stem Cell. Alfonso Martínez Arias, a developmental biologist at the University of Pompeii Fabra in Barcelona, Spain, says this shows that the blasts are still not replicas of a normal embryo. For now, he says, “It clearly doesn’t work.”
This is possible because a normal embryo develops from an egg and is then fertilized by a sperm. A blastoid made from stem cells can express the same genes as a normal embryo, but lacks a key element that normally comes from an egg, says Martinez-Aria.
There’s also a chance the team could see more progress if the experiment were done in more monkeys. After all, only five of the 484 blastoids that were germinating at day seven survived, 17. Getting an embryo to implant in the uterus is a difficult task, Chuva de Sousa Lopez said. “Even when you do IVF in humans, it’s one of the hurdles to getting pregnant,” she says. Maybe if you did this with 100 monkeys, you’d have the two most likely to get pregnant.
Monkey life is precious, Martínez Arias says, and such large-scale experiments are probably not considered ethical.
None of this means that the explosions are not useful. They still provide a good model of what happens in the early stages of embryonic development in monkeys and humans.
Researchers hope monkey fossils will help us learn more about human embryos. We don’t know much about how the union of sperm and egg leads to the development of our bodies and nervous systems, and why things sometimes go awry. Scientists are generally not allowed to study human embryos in the lab more than 14 days after fertilization. And recently published international guidelines stress that human implants should never be implanted in humans or other animals.
“We want to understand human development, and it is not safe to transfer human explosions [into people]” says Revron. “We have to find an alternative. And non-human primates are close relatives to humans.
Scientists hope they can tell us more about human pregnancy, including why some people struggle to conceive and why some miscarriages occur. Because scientists can generate numbers without blasts, they don’t need to rely on animals as embryo donors. Naomi Morris, who researches embryo development at London’s Crick Institute and hopes to find ways to improve IVF, can test drugs on hundreds or thousands of blastoids.