The northern white rhinoceros is one of the world's most endangered species — a mere seven beasts are alive today. But new research may offer the threatened rhinos a new hope. Scientists say they have produced the first stem cells from two different endangered species — the white rhino and a west African monkey called a "drill." These stem cells could be used to create sperm and eggs for artificial reproduction, and thus save the species from extinction. How would this work? Here's what you need to know:

How were the stem cells made?
Since the 1970s, scientist Oliver Ryder had been collecting frozen skin cells from more than 800 endangered species. He calls it the "Frozen Zoo," and has always hoped that one day technology would be developed to use those cells to save the endangered animals. Over a five-year process of trial and error, Dr. Jeanne Loring was able to generate stem cells from those frozen skin cells through a process called "induced pluripotency," which inserts specific genes in normal cells, sparking the transformation into stem cells.

How would this save an endangered species?
"Pluripotent" stem cells are theoretically capable of making any tissue in the body, says Ewen Callaway at Nature. That includes sperm and egg cells, which could be used in assisted captive breed programs. In other words, scientists could manufacture reproductive cells to be used for in vitro fertilization, or create an embryo from eggs and sperm generated from stem cells, and implant those embryos in endangered animals, says Marlowe Hood for AFP.

Will this really work?
This should be a "last-ditch effort," says conservation scientist Robert Lacy, as quoted by BBC News. There are still "simpler, cheaper, and more effective ways" to rescue endangered species. And reproductive biologist William Holt warns that by the time species are as endangered as the white rhino, it's too late for the stem cell technique to work. "I think it's a bit of a stunt," he says, as quoted by Nature. Too little is known about the reproductive biologies of these endangered animals, he argues, for this technique to be effective on a large scale.

What other applications does this research have?
Though it's the reproductive applications of the research that has scientists most excited, the early applications will likely be medicinal, says Richard Black at BBC News. Animals suffering from diseases like diabetes, for example, could benefit from stem cells that are turned into replacements for cells that cease to function properly.

Sources: AFP, BBC News, International Business Times, Nature