Irish Polar Bears?
Apparently, the female ancestor of present-day polar bears was a brown bear, living in what presently corresponds to Ireland. An international research team has used mitochondrial DNA (see figure 1) to trace back the polar bears (maternal) ancestry. And it turns out that, 20,000 to 50,000 years ago, they interbred with brown bears.
Figure 1: During fertilization, the sperm cell does not contribute mitochondria to the egg.
(Source: http://www2.le.ac.uk/departments/emfpu/genetics/explained/mitochondrial)
Despite the obvious differences in body size, skin and coat color, tooth type, fur…