From Adrian Barnett at New Scientist, reviewing Mark Maslin’s
All this allows Maslin to buttress his central contention, that human evolution as we know it wouldn’t have occurred without the uplift of the Tibetan plateau and the formation of the Great Rift valley. These events, and the cycling between salt flats and shallow sea that mark the history of the Mediterranean, are the great drivers of human evolution – the climatic starting gun that set off the human race.
Maslin also provides a fine overview of the evolution of evolutionary thinking over the past 150 years, to the point where we now see it less as an orderly march towards an inevitable Homo sapiens and more of a random stumble to now.
Randomness and climate change are big now, global. It’s not clear from the discussion why, if those factors were so important, they did not affect other contemporary life forms.
One of the fundamental questions of our existence is why we are so smart. There are lots of drawbacks to having a large brain, including the huge food intake needed to keep the organ running, the frequency with which it goes wrong, and our very high infant and mother mortality rates compared with other mammals, due to the difficulty of giving birth to offspring with very large heads. So why did evolution favour the brainy ape? This question has been widely debated among biological anthropologists, and in recent years, Maslin and his colleagues have pioneered a new theory that might just be the answer.
Looking back to a crucial period some 1.9 million years ago, when brain capacity increased by as much as 80%, The Cradle of Humanity explores the implications of two adaptive responses by our hominin ancestors to rapid climatic changes – big jaws, and big brains. Maslin argues that the impact of changing landscapes and fluctuating climates that led to the appearance of intermittent freshwater lakes in East Africa may have played a key role in human evolution. Alongside the physical evidence of fossils and tools, he considers social theories of why a large, complex brain would have provided a major advantage when trying to survive in the constantly changing East African landscape.
As to the variety of reasons why we are smart, see also: Retroviruses play a role in development of human brain?
Tooth size not linked to brain size in early humans
Large human brain size easily explained?
Human origins: The war of trivial explanations
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