Scientists have cleared a significant hurdle in the years-long effort to save Africa’s northern white rhinoceros from extinction with the first-ever rhino pregnancy using in vitro fertilization.
The lab-assisted pregnancy, which researchers will announce today, involved implanting a southern white rhino embryo in a surrogate mother named Curra.
The advance provides the essential “proof of concept” that this strategy could help other rhinos, says Jan Stejskal of the BioRescue project, the international group of scientists leading this research. Curra died just a couple months into her 16-month pregnancy from an unrelated bacterial infection, Stejskal says, but the successful embryo transfer and early stages of pregnancy pave the way for next applying the technique to the critically endangered northern white rhino.
The process was documented exclusively by National Geographic for an upcoming Explorer special currently slated to air in 2025 on Nat Geo and Disney+.
BioRescue expects to soon implant a northern white rhino embryo into a southern white rhino surrogate mother. The two subspecies are similar enough, according to the researchers, that the embryo will be likely to develop.
Eventually this approach may also help other critically endangered rhinos, including the Asian Javan rhinoceros and the Sumatran rhinoceros, which each now number under 100 individuals, Stejskal says.
But the northern white rhino’s current situation is the most pressing by far. There are no males left, and the only two remaining animals are both elderly females that live under armed guard on a reserve in a 700-acre enclosure in Kenya called Ol Pejeta Conservancy.
The boxy-jawed animals once roamed across central Africa, but in recent decades their numbers have plummeted due to the overwhelming international demand for their horn, a substance used for unproved medicinal applications and carvings. Made from the same substance as fingernails, rhino horn is in demand from all species, yet the northern white rhino has been particularly hard-hit.
These rhinos “look prehistoric, and they had survived for millions of years, but they couldn’t survive us,” says Ami Vitale, a National Geographic Explorer and photographer who has been documenting scientists’ efforts to help the animals since 2009.
“If there is some hope of recovery within the northern white rhino gene pool—even though it’s a substantially smaller sample of what there was—we haven’t lost them,” says conservation ecologist David Balfour, who chairs the International Union for the Conservation of Nature’s African rhino specialist group.
Blueprints for rhino babies
To stave off the animal’s disappearance, BioRescue has used preserved sperm from northern white rhinos and eggs removed from the younger of the two remaining females. So far, they’ve created about 30 preserved embryos, says Thomas Hildebrandt, the head scientist of BioRescue and an expert in wildlife reproduction based at the Leibniz-Institute of Zoo and Wildlife Research in Berlin.
Eventually the team plans to reintroduce northern white rhinos into the wild within their range countries. “That’d be fantastic, but really, really far from now—decades from now,” says Stejskal.
Worldwide, there are five species of rhinoceros, and many are in trouble. Across all of Africa there are now only about 23,000 of the animals, and almost 17,000 of them are southern whites. Then there are more than 6,000 black rhinos, which are slightly smaller animals whose three subspecies are critically endangered. In Asia, beyond the critically endangered Javan and Sumatran rhinos, there’s also the greater one-horned rhino, whose numbers are increasing and currently are estimated to be around 2,000.
The BioRescue effort has experienced many setbacks, and even though the team now has frozen embryos, the clock is ticking. The researchers intend to use southern white rhinos as surrogate moms for the northern white rhino embryos, but the scientists want any northern white rhino calves to meet and learn from others of their kind, which means they need to be born before the two remaining females die.
“These animals learn behaviors—they don’t have them genetically hard-wired,” says Balfour, who’s not involved with the BioRescue work. But birthing new animals in time will be a challenge. “We’re really skating on the edge of what’s possible,” he says, “but it’s worth trying.”
Najin, the older female, will be 35 this year, and Fatu will be 24. The animals, which were born in a zoo in the Czech Republic, are expected to live to about 40, says Stejskal, who also serves as director of international projects at the Safari Park Dvůr Králové, the zoo where the animals lived until they were brought to Kenya in 2009.
Impregnating a rhino
The next phase of BioRescue’s plan involves implanting one of their limited number of northern white rhino embryos into a southern white rhino surrogate mother—which the group plans to do within the next six months, Stejskal says.
They’ve identified the next surrogate mother and set up precautions to protect her from bacterial infections, including a new enclosure and protocols about disinfecting workers’ boots. But now they must wait until the female rhino is in estrus—the period when the animal is ready to mate—to implant the egg.
To identify that prime fertile time, they can’t readily perform regular ultrasounds at the conservancy as they might do in a zoo. Instead they have enlisted a rhino bull that has been sterilized to act as a “teaser” for the female, Hildebrandt says, adding that they must wait a few months to make sure that their recently sterilized male is truly free of residual sperm.
Once the animals are brought together, their couplings will alert conservancy staff that the timing is right for reproductive success. The sex act is also important because it sets off an essential chain of events in the female’s body that boosts the chances of success when they surgically implant the embryo about a week later.
There’s little chance the conservancy staff will miss the act. White rhinos typically mate for 90 minutes, Hildebrandt says. What’s more, while mounted on the females, the males often use their temporary height to reach tasty plant snacks that are generally out of reach.
Boosting genetic diversity
With so few northern white rhinos left, their genetic viability may seem uncertain. But the BioRescue team points to southern white rhinos, whose numbers likely dropped to less than 100, and perhaps even as few as 20, due to hunting in the late 1800s. Government protections and intense conservation strategies allowed them to bounce back, and now there are almost 17,000.
“They have sufficient diversity to cope with a wide range of conditions,” says Balfour. Researchers don’t know exactly how many southern white rhinos existed a century ago, he says, but it’s clear that the animals came back from an incredibly low population count and that they now appear healthy.
Beyond their small collection of embryos, the BioRescue team hopes to expand the northern white rhino’s gene pool by drawing from an unconventional source—skin cells extracted from preserved tissue samples that are currently stored at zoos. They aim to use stem cell techniques to reengineer those cells and develop them into sex cells, building off similar work in lab mice.
According to their plan, those lab-engineered sex cells would then be combined with natural sperm and eggs to make embryos, and from there, the embryos would be implanted into southern white rhino surrogate mothers.
Such stem cell reprogramming work has previously led to healthy offspring in lab mice, Hildebrandt says, but rhinos aren’t as well-studied and understood as mice, making this work significantly challenging.
A global effort
The northern white rhino revitalization venture has cost millions of dollars, supported by a range of public and private donors, including the German Federal Ministry of Education and Research. Other partners on the effort include the Leibniz Institute for Zoo and Wildlife Research, the Czech Republic’s Safari Park, the Kenya Wildlife Service, Ol Pejeta Conservancy, and also Katsuhiko Hayashi, a professor of genome biology at Osaka University in Japan who conducted the mouse stem cell research.
Building upon Hayashi’s stem cell techniques could ultimately bring the northern white rhino gene pool up to 12 animals—including eggs from eight females and the semen of four bulls, according to Stejskal.
An alternative approach to making more babies, like crossbreeding northern and southern white rhinos, would mean the resulting calves wouldn’t be genetically pure northern white rhinos, Hildebrandt notes. The two subspecies look quite similar, but the northern version has subtle physical differences, including hairier ears and feet that are better suited to its swampy habitat.
The two animals also have different genes that may provide disease resiliency or other benefits, Hildebrandt says, and there are unknown potential differences in behavior and ecological impact when populating the area with southern white rhinos or cross-bred animals.
The northern white rhino “is on the brink of extinction really only due to human greed,” Stejskal says. “We are in a situation where saving them is at our fingertips, so I think we have a responsibility to try.”
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