In the 20 years since the release of the film Jurassic Park, DNA cloning technologies have advanced dramatically. Professor Adam Hart asks whether we could and should start bringing extinct animals back from the dead.

The fossilised remains of dinosaurs are too degraded to hold any viable DNA, so Jurassic Park is unlikely to be a reality. But what about Pleistocene Park? Deep frozen remains of Arctic animals like the woolly mammoth or the Irish elk, have been shown to contain DNA - but is it in a good enough condition to rebuild the genome and attempt cloning these animals which became extinct nearly 4000 years ago?

Some people think it could work. But should we even be considering it? With so many plants and animals threatened with extinction now, should we be wasting time and resources on bringing back animals that didn't make the cut?

Adam Hart asks experts in ancient DNA whether the code for life could be resurrected in animals such as the mammoth, the passenger pigeon, the dodo, the marsupial tiger, or the thylacine. And he asks conservationists whether we should be doing it.