Many popular animals kept in zoos across Europe have become deeply inbred and have very little "genetic integrity", a new report reveals.
A study by conservation geneticist Dr Paul O'Donoghue at the Aspinall Foundation found that the pedigrees of many zoo animals have become contaminated by hybridisation with different but related species.
The study examined the DNA of nine "founder" animals which all 110 captive cats are descended from and found that they were all closely related.
"It means the animals alive now are all related, mostly sharing more DNA than if they were cousins," O'Donoghue told the Sunday Times.
"When such close relatives mate, their offspring become inbred, meaning they face stillbirths, genetic diseases and shorter lives."
Hundreds of breeding programmes are operated by European zoos for rare and endangered species. These programmes were mostly founded between 20 to 30 years ago using small populations of animals that were assumed to be unrelated.
However, modern DNA testing has revealed these assumptions to be false, raising doubts about the value of these conservation schemes.
O'Donoghue also examined the Scottish wildcat, which is displayed in zoos across Britain, and found that almost all of the 60 or so studied are actually partly domesticated cats because their recent forebears mated with different species.
"There are also grave doubts about the genetic integrity of many other iconic species," O'Donoghue explained.
"They all have the same features of being descended from small founder populations in the days before DNA testing could show if those animals were pure-bred or unrelated.
"Now we can test their descendants, it is clear that people who visit zoos to see iconic animals are often looking at hybrids which have zero conservation value."