The Northern White Rhinoceros (\(Ceratotherium\) \(simum\) \(cottoni\)) is a distinct subspecies of the white rhinoceros, once found roaming across parts of Central and East Africa. Today, the fate of this entire population rests on just two individuals, a mother and daughter named Najin and Fatu. Both rhinos are female and reside under constant protection at the Ol Pejeta Conservancy in Kenya. Their existence represents a profound biological crisis, known as functional extinction. This term signifies that although individuals remain, the subspecies can no longer recover through natural means. Unprecedented scientific efforts are the only path left to reverse this loss and re-establish a viable population.
The Immediate Biological Crisis
The current biological crisis stems from the fact that the two remaining female northern white rhinos are physically unable to carry a pregnancy to term. Najin, the elder female, has age-related problems and the presence of small, benign tumors and cysts within her reproductive tract. These conditions prevent her from safely conceiving or sustaining a calf. Fatu, the younger female, also has a significant reproductive problem due to a degenerated uterine lining, making her uterus unsuitable for implantation and gestation.
The last male of the subspecies, Sudan, died in 2018, confirming functional extinction and eliminating any possibility of natural reproduction. Recovery is entirely dependent on advanced scientific intervention. The historical decline was driven by intense poaching for their horns and extensive habitat loss.
Creating Viable Embryos
The initial phase of the scientific rescue mission focuses on using Assisted Reproductive Technology (ART) to create viable embryos outside the body. This process involves a highly specialized form of in vitro fertilization (IVF), which begins with the harvesting of eggs, or oocytes, from the remaining female, Fatu.
The procedure, known as ovum pick-up (OPU), requires Fatu to be fully anesthetized while a team of specialized veterinarians collects the immature egg cells using a two-meter-long device guided by ultrasound. Once collected, the oocytes are flown to specialized laboratories in Italy where they are prepared and fertilized using cryogenically preserved sperm. This sperm was collected and banked from deceased male northern white rhinos, such as Suni and Sudan.
Fertilization is achieved using Intracytoplasmic Sperm Injection (ICSI), where a single sperm is injected directly into the egg cell. The fertilized eggs are then cultured for several days to see if they develop into a blastocyst, the stage at which an embryo is viable for transfer or cryopreservation. This process is challenging because the viability of the harvested oocytes is often low, and the techniques must be adapted specifically for the rhino’s unique reproductive biology. Despite these difficulties, international collaboration has successfully created and cryopreserved 38 pure northern white rhino embryos, which are currently stored in liquid nitrogen in laboratories in Germany and Italy. These cryopreserved embryos represent the future of the subspecies.
Establishing a Surrogate Population
Because neither Najin nor Fatu can safely carry a calf, the resulting northern white rhino embryos must be implanted into surrogate mothers. The closely related Southern White Rhino (\(Ceratotherium\) \(simum\) \(simum\)) has been chosen to serve as the surrogate population. This related subspecies is biologically similar enough to provide a suitable environment for the northern white rhino embryos to develop.
The implementation of the surrogate program is a massive undertaking, requiring the development of specialized techniques for embryo transfer in a large animal. The length of the rhino’s reproductive tract presents a significant logistical hurdle, demanding the invention of new instruments and protocols to successfully place the tiny embryo. Scientists first achieved a major milestone by successfully transferring a Southern White Rhino embryo into a surrogate, resulting in a 70-day pregnancy that provided proof of concept.
Following this success, the team has now initiated the transfer of pure northern white rhino embryos into prepared Southern White Rhino surrogates at the Ol Pejeta Conservancy. This final step is delicate, as it requires the surrogate mother to be prepared hormonally and monitored closely throughout the entire 16-month gestation period. The hope is that the surrogate mothers will not only carry the calves to term but also raise them, allowing the new northern white rhino calves to learn essential species-specific behaviors from their adopted mothers.
Expanding the Genetic Pool
While the existing embryos offer an immediate path to preventing complete extinction, the limited number of donors—two females and a few deceased males—does not provide enough genetic diversity for a healthy, self-sustaining population. This long-term challenge is being addressed through cutting-edge stem cell technology to expand the genetic pool far beyond the current living and deceased donors.
Induced Pluripotent Stem Cells (iPSCs)
The strategy involves the creation of Induced Pluripotent Stem Cells (iPSCs) from stored tissue samples, such as fibroblasts, collected from 12 deceased northern white rhinos over the past decades. Scientists are able to reprogram these specialized skin cells back into a primitive, embryonic-like state where they can theoretically differentiate into any cell type. The ultimate goal is to guide these iPSCs to mature into new sperm and egg cells, known as gametes.
Long-Term Genetic Health
This process would unlock the genetic material of the 12 rhinos whose tissue was preserved, effectively multiplying the number of potential parents for the future population. By introducing genetic variation from these animals, the scientists aim to prevent the severe inbreeding depression that would occur if the subspecies were founded only on the current 38 embryos. The resulting stem cell-derived gametes could then be used in future IVF procedures, ensuring that the restored northern white rhino population has the robust genetic foundation necessary for long-term survival in the wild.