In particular, melting ice caps mean less room for polar bears, seals and penguins to live and breed - and most species cannot migrate or evolve fast enough to keep up.

It's new, complex and evolving fast.

In contrast, the introns are under fewer selective constraints and tend to evolve faster.

Rodents have a much shorter generation time than humans, and so the theory was that they would have much faster mutation rates, and so evolve faster.