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From David Nowel

I was interested to read about the demise of the warrah or Falklands fox which had formed the basis of Charles Darwin’s first musings about evolution (20 December 2003, p 80). Once isolated, this wolf-like canine inhabiting the main East and West Falkland islands appeared to be evolving into separate and distinct species.

The isolation of such a large carnivore would have rightly puzzled many 19th-century scientists. But Darwin was a fellow of the Geological Society and held the Wollaston medal – still the highest honour in earth science. He would thus find the answer in geology, which was equally significant in developing his revolutionary ideas.

Our present Quaternary climate has been punctuated by ices ages roughly every 100,000 years, during which global mean sea level fell significantly as vast ice sheets developed, removing water from the oceans. Global sea levels fell by at least 120 to 150 metres on average, depending on how this is measured. As the Falkland islands are now separated from Patagonia and the Argentine mainland by just over 150 metres of water at the deepest point, it is probable that these islands became a peninsula during the last ice age, which ended roughly 11,500 years ago.

Thus South American foxes became established in the unglaciated Falklands some time before 20,000 years ago, and were then isolated as the sea started to rise. In turn the weight of an extra 120 metres of water depressed the edge of the modern continental shelf by roughly a further 35 metres. Britain and Ireland also formed a peninsula during the last ice age and later developed an impoverished flora and fauna compared with continental Europe.

New Barnet, Hertfordshire, UK