The San Diego Zoo Wildlife Alliance is home to the world’s last two remaining northern white rhinos. The future is bleak for this species, but the alliance’s special Frozen Zoo is hard at work to ensure that the legacy of these species is not lost forever.

First and foremost, what is a frozen zoo? The term refers to a portion of the zoo’s pathology department that is freezing cellular samples of endangered species so that even if they go extinct, they are not ever truly lost. So far, the zoo has saved cell samples of 10,000 individuals from 1200 species and subspecies.

Marlys Houck, the curator of the frozen zoo, explains that she and other researchers freeze living cells in liquid nitrogen, stopping them from dividing, and effectively holding them in suspended animation for decades.

The Frozen Zoo was founded in 1975 by Dr. Kurt Benirschke who had a Jurassic Park-like dream of preserving threatened species in preparation for the scientific advancements of the future. In line with Benirschke’s vision, scientists at the zoo are now able to theoretically use the frozen cells to create stem cells that could be used to make sperm and eggs in the future.

Dr. Barbara Durrant, another contributor to the zoo, emphasizes that this work should not be seen as an alternative to conservation efforts, but rather as a “plan B.” She says, “We have to always be careful in our education and in our publicity speaking to the public about this; that we don’t give a false impression that science can solve all the problems of conservation. That’s not the case.”

The researchers behind the Frozen Zoo might be long retired by the time science has achieved a way to clone animals from cell samples, but with enough advancement, their work could be used to revive species nearly lost forever. Houck says, “Of course we don’t want to ever lose the last animal, but if we do, at least we can bank some part of it in the Frozen Zoo for the future.”