Science Week: Piecing together the jigsaw of climate change and human evolution

This post was contributed by Guy Collender, of Birkbeck’s Department of External Relations.

Dr Phil Hopley, of Birkbeck's Department of Earth and Planetary Sciences

Dr Phil Hopley exhibited replica skulls of our ancestors during Science Week. Photo: Harish Patel

I knew an unusual presentation was in store as soon as I saw six skulls menacingly positioned at the front of the lecture theatre. The exhibits – all different shapes and sizes – immediately caught the audience’s attention, and our questions about their origins were answered in the fascinating hour that followed.

Dr Phil Hopley began Birkbeck’s series of Science Week lectures with a talk on 16 April about the links between climate change and human evolution. He used the skulls – five replicas of our ancestors and one gorilla skull – to illustrate how evolution is all about the changing dimensions of the head as it has become rounder and larger to accommodate a bigger brain over millions of years. In comparison, the gorilla’s skull includes ferocious canines and space for huge powerful jaws – it certainly sent a shiver up my spine being only a few feet away from my seat.

A family tree dating back millions of years
Dr Hopley, of Birkbeck’s Department of Earth and Planetary Sciences, explained how the last common ancestor of chimpanzees and modern humans was on this planet about six of seven million years ago. Both branches of the family tree then developed separately, with chimpanzees on the one hand, and about 20 species of hominins – the ancestors of modern humans – walking on two legs on the other. As the hominins evolved, they became characterised by their tool use, larger brains, language and art, eventually developing into Homo sapiens – our own species. But our ancestral line has not been straightforward, and Dr Hopley highlighted the complexity. He said: “Homo sapiens is the only human species alive today, but for most of human evolution there have been a number of co-existing human species.”

As Dr Hopley explained, hominin fossils have mainly been found in two areas – the Rift Valley in East Africa (dating back five million years), and caves in Southern Africa (dating back 2.5 million years). Yet, hardly surprising, given the awesome amount of time involved, it is very rare to find a whole hominin specimen. What is clear is that the human fossil record is very incomplete, both geographically and temporally, and solving the mystery is a bit like piecing together a jigsaw.

Climate change: from forest to grassland
The question of why our ancestors evolved to become bipedal was then addressed, and this was where Dr Hopley referred to his work studying fossils from caves in South Africa. The study of carbon and oxygen isotypes and climate modelling has shown that the savannah in Africa developed eight million years ago due to the reduction in carbon dioxide and reduction in rainfall. As the grasslands replaced the forests, our ancestors evolved to walk on two feet as they needed to cover large distances to search for food, which wasn’t necessary when they were still living in the forest. Although it’s difficult to build up a comprehensive understanding of how climate change drives evolution, Dr Hopley did present a general conclusion. He said: “Human evolution did occur because of climate change in the broad sense as forests were replaced by savannah.”

I’ve never been to a lecture with skulls on display before and I’ll certainly never forget this one. It was a powerful way to remind us that our common ancestors adapted to the African bush and started walking when the forests began to recede.


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