Darwin would have loved this:
A study of prehistoric animals has revealed the crucial role of the English Channel in shaping the course of Britain's natural history. The Channel acted as a filter, letting some animals in from mainland Europe, but not others.
Even at times of low sea level, when Britain was not an island, the Channel posed a major barrier to colonisation. This was because a massive river system flowed along its bed…
"We find we're getting only a selection of the mammals during the British interglacials that there are in mainland Europe," said Professor Stringer [of London's Natural History Museum]. "For example, at one pre-historic site, researchers found hippopotamus and fallow deer; but unlike mainland Europe at the time, there were no horses and no humans. This suggests that the Channel, or the Channel river system, is acting as a filter to prevent the movement of some of these [mammal] forms into Britain."
Colonisation of islands was a subject of great importance to Darwin. He devoted chapters 11 and 12 of Origin of Species to the geographical distribution of species, and islands figured heavily in his theories of speciation. He was mainly interested in mid-ocean islands, such as the Galapagos Islands, but he was always on the lookout for examples of how species could become isolated from parent stock.