Read more: 鈥�10 biggest puzzles of human evolution鈥�
SHARP stone flakes found two decades ago in a parched riverbed in the Afar region of Ethiopia are the oldest tools yet discovered. They date from 2.6 million years ago. It would be another million years before our ancestors made their next technological breakthrough. Then, instead of using the chips off a river cobble as blades and scrapers, someone realised that the cobble itself could be worked into a tool. 鈥淚t is recognisable as a hand axe, but very rough,鈥� says Dietrich Stout of Emory University, Atlanta. Another million years passed before early modern humans perfected this technique. What took them so long?
Intelligence must have played a part. In the 2 million years after the appearance of the first tools, hominin brain size more than doubled, to around 900 cubic centimetres. Toolmaking undoubtedly requires smarts, and Stout has used MRI scans of people knapping stones to find out which brain areas are involved. The studies suggest that early technological innovations depended on novel perceptual-motor capabilities 鈥� such as the ability to control joint stiffness 鈥� while later developments were underpinned by growing cognitive complexity, including the sort of recursive thinking required for language (). So, although tools appear not to develop much, their production is underpinned by great cognitive advance, leading Stout to conclude that there was more progress during this period than we tend to think. What鈥檚 more, he says, people may have made other tools from materials such as wood and bone that perished long ago.
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鈥淓ven allowing for that, stone-tool progress looks painfully slow,鈥� says Chris Stringer of the Natural History Museum in London. In his book The Origin of Our Species (Allen Lane, 2011) he identifies another reason 鈥� demography. 鈥淚t鈥檚 not what you know, it鈥檚 who you know,鈥� he says. Modern humans have large populations with lots of people copying and many ways to pass on information. Our long lives also permit transfer of ideas down the generations, whereas Homo erectus and Homo heidelbergensis probably had a maximum lifespan of around 30 years, and Neanderthals maybe 40. 鈥淭hey鈥檙e having to grow up very fast and there鈥檚 much less networking between groups,鈥� Stringer says.
鈥�15W Energy consumption of a human brain鈥�
Furthermore, our ancestors may have shunned change since life would have been challenging enough without risky experimentation. 鈥淚t鈥檚 dangerous to go around innovating and inventing,鈥� says Stringer. Mark Pagel at the University of Reading, UK, doubts that hominins before Homo sapiens had what it takes to innovate and exchange ideas, even if they wanted to. He draws a comparison with chimps, which can make crude stone tools but lack technological progress. They mostly learn by trial and error, he says, whereas we learn by watching each other, and we know when something is worth copying. If Pagel is correct, then social learning is the spark that ignited a technological revolution (Wired for Culture, Penguin, 2011). 鈥淲ith the arrival of modern humans the game changed,鈥� he says.
