How climate change spurred human intelligence evolution

Scientists show shifts from dry to wet and back in East Africa's Rift Valley caused the development of the human brain

Humans evolved their very large brains in response to the dramatic shifts in the climate of East Africa, the cradle of humanity where man's ancestors are thought to have originated about two million years ago, a study has suggested.

Scientists have matched exceptionally wet periods and very dry periods in the East African Rift Valley to sudden spurts in the evolution of the hominid ancestors of Homo sapiens, which resulted in the evolution of the modern human brain.

Academics have long argued about what led to the unusually large brain of humans with its capacity for language, abstract thought and consciousness.

The latest theory suggests it was triggered by the need to adapt to dramatic changes in the local environment of early man.

"It seems modern humans were born from climate change, as they had to deal with rapid switching from famine to feast - and back again - which drove the appearance of new species with bigger brains and also pushed them out of East Africa into Eurasia and South Africa," said Prof Mark Maslin of University College London, the co-author of the study published in Plos-One.

The Rift Valley is an extensive geological fault marked by mountains, lakes and fertile valleys. Many of the most important fossil remains of early humans have been unearthed in the region, leading to suggestions that it was the most important place for the early origins of man.

The study looked at climate change over the past five million years, where there have been large fluctuations between wet periods where lakes were far higher than they are today and dry periods where sand dunes formed in former lake beds. The scientists found that there were relatively short periods lasting about 200,000 years when East Africa became very sensitive to the cyclical changes in the Earth's orbit around the Sun-known as Milankovitch cycles - which lead to global-scale changes to the climate, such as ice ages.

- The Independent