The last male northern white rhino, named Sudan, died on March 20, 2018. He leaves behind two females—both unable to reproduce naturally—along with any hope of saving the species without scientific intervention.

Of the six species of rhino, the northern white is by far the most critically endangered, but all face the very real risk of extinction. According to conservationists, only 67 Javan rhinos remain in Indonesia’s tropical Ujung Kulon National Park. Fewer than 100 Sumatran rhinos, the smallest species, are scattered across Southeast Asia and the Indian subcontinent, which is also home to an estimated 3,500 greater one-horned rhinos. In southern and eastern Africa, between 5,000 and 5,500 black rhinos live in a wide range of habitats that occasionally overlap with those inhabited by the southern white—the most populous species, numbering around 20,000.

As their numbers dwindled and their prospects for survival narrowed, researchers collected northern white rhino semen and stored the samples in liquid nitrogen. Now, they hope to harvest eggs from the females, which are housed in a nature reserve, and transfer the embryo to a healthy surrogate from the more common southern white species.

The average northern white rhino weighs between 3,800 and 5,300 pounds, or somewhere between an average mid-size sedan and a full-size SUV. Larger animals stand just shy of the height of the average American adult man (five feet, ten inches) and can grow horns that measure nearly five feet in length. It is for this horn that rhinos are so prized—and therefore so endangered.

Unlike horns from other mammals, like antelope and bighorn sheep, rhino horns are comprised entirely of keratin. The protein is found in hair, nails, human skin, and cosmetic products (especially shampoos, conditioners, and various other hair treatments).

In Southeast Asia, rhino horns are ground up for use in traditional medicines. In many of those countries, the powder is considered an aphrodisiac or hangover cure. And more commonly, especially in recent years, the horns are kept intact for display as symbols of wealth and social status. High demand means high rewards for successful poachers, driving the value of rhino horns beyond their weight in gold or cocaine. This has spelled disaster for wild-dwelling populations who also face habitat encroachment and other threats.

Nature sanctuaries, zoos, and aquariums have allowed wildlife biologists to manage threatened and endangered animal species, in many cases creating a safety net against extinction. These efforts, coupled with and supported by animal research, are the only way to mitigate the destructive impact human activities have had on species like the northern white rhino.

“There’s no doubt that if northern white rhinos hadn’t existed in zoos, then the species would now be completely extinct,” conservationist Richard Vigne told CBS News. Nature reserves have also afforded researchers the opportunity to successfully test—in southern white rhinos—the in-vitro procedure they hope will work just as well for the near-extinct northern species.

Animal research has improved the health and reproductive outcomes of animals in captivity in ways that could potentially save endangered species from the brink of extinction. Some recent findings and relevant ongoing projects include:

The discovery of the role of stress hormones in diseases that affect the black rhino in studies that have led to changes in the animals’ housing;

findings that sociality affects ovarian cycles in African elephants;

new understandings of the genetic and hormonal predictors of successful reproduction in the endangered African painted dog. This research has reaffirmed the importance of genetic diversity; and

a non-invasive means of detecting pregnancy in the feces of cheetahs, leopards, and domestic cats.

Climate change, poaching, and habitat loss are complex problems without easy solutions. But as humans have begun to understand the impact of their actions on wildlife, researchers have introduced new strategies to preserve populations of vulnerable animals. Much of what is now known about conservation has been learned through research with animals conducted at zoos, aquariums, and nature reserves that house them in captivity. Additionally, highly trained veterinarians provide attentive, high quality care for the animals in their charge.

Based on their success in previous trials with southern white rhinos, scientists are confident the in-vitro approach may save the prehistoric-looking northern white rhino from extinction. Without conservation efforts backed by animal research, the animals’ skeletons would perhaps be chosen as the next exhibit featured in the dinosaur collection at the Smithsonian’s National Museum of Natural History.

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Pictured at top: Fatu, descendant of Sudan, one of the only two surviving female northern white rhinos.