Evolution and the Ice Age

Looking back at the earth’s geological record it is clear that past ecosystems were very different from those we see today. Over 65 million years ago, for example, dinosaurs formed a key part of the earth’s ecosystem.

Dr John Stewart from BU’s School of Applied Sciences has studied the interaction between ancient ecosystems – paleoecology – and evolution of humans and other organisms over the last 100,000 years, undertaking everything from excavating cave sites in Belgium to exploring the desert of Abu Dhabi.

In one study Dr Stewart has taken existing knowledge of the geographical spread of plant and animal species throughout the warming and cooling of the Ice Ages to provide insights into human origins, including the evolution and extinction of Neanderthals.

He has also examined the rise of the ‘first Europeans’, along with the Denisovans – a newly discovered group – mysterious cousins of the Neanderthals, who occupied a vast realm stretching from the cold expanse of Siberia to the tropical forests of Indonesia.

The key insight in this work, conducted alongside Professor Chris Stringer of London’s Natural History Museum, came from understanding the important role of the refuge taken by a species from harsher conditions – known as a refugium – which influences the evolutionary future of the species. Once the climate changes again, for instance as ice sheets melt, these refugia populations can expand or connect up again.

Evolution has also had a huge influence. The inhabitants are not the same as the original populations as a result of genetic mutations. The time spent apart in refuge generally serves to splinter a once unified species.

Previous research into hedgehogs, polar bears and other animals suggest that, even once an Ice Age ends and the different populations start intermingling again, they never really merge back together as a single group. This process drives important evolutionary changes, which can ultimately lead to the origins of a new species.

Ultimately, this explains why Homo sapiens are still here and other human species went extinct some 30,000 years ago: our ancestors chose the right refuge to wait out the Ice Age. Today, Dr Stewart’s work has shifted away from fossil remains to ancient DNA.

“The most exciting development in my field has been the ability to analyse ancient DNA, which has begun to allow us to see evolution happening over the last several dozen thousand years,” explains Dr Stewart.

Dr Stewart’s work is not confined to the past, informing the present too. Recently there had been a proposal to eradicate the Eagle Owl because it killed other birds, such as hen harriers, and was not thought to be a native species. But Dr Stewart’s studies of fossils and more recent archaeological records revealed the bird, or something like it, has been present in Britain for up to 700,000 years. The plan to cull the birds has now been abandoned.