For animals extinct in the wild, even zoos may not be good enough

Scientists say human activity has pushed Earth into the sixth, with species disappearing 100 to 1,000 times more quickly than normal

For species classified as "extinct in the wild", the zoos and botanical gardens where their fates hang by a thread are as often anterooms to oblivion as gateways to recovery, new research has shown.

Re-wilding what are often single-digit populations faces the same challenges that pushed these species to the cusp of extinction in the first place, including a lack of genetic diversity. But without conservation efforts, experts say, chances of these species surviving would be even smaller.

Since 1950, nearly 100 animal and plant species vanquished from nature by hunting, pollution, deforestation, invasive lifeforms and other drivers of extinction have been put into critical care by scientists and conservationists, according to the findings.

While the category "extinct in the wild" was not added to the benchmark Red List of Threatened Species until 1994, the term could have applied to all of them.

Of these species teetering on the edge, 12 have been reintroduced to some degree back into the wild, according to a pair of studies published last week in the journals Science and Diversity.

Another 11, however, have gone the way of dinos, dodos and dozens of Pacific island trees, whose delicate flowers will never again grace the planet.

Biodiversity loss has reached crisis proportions not seen since an errant asteroid as big across as Paris smashed into Earth 66 million years ago, wiping out land dinosaurs and ending the Cretaceous period.