Since 1975, San Diego Zoo has been deep-freezing cell samples from rare species. Scientists are now using the collection to try to save species like the northern white rhinoceros. Show more
Discover 11,128,835 listings and 280,372 playable programmes from the BBC
Since 1975, San Diego Zoo has been deep-freezing cell samples from rare species. Scientists are now using the collection to try to save species like the northern white rhinoceros. Show more