Thirty-five thousand years ago, a diminutive innovation transformed India. The advent of stone microblades set the stage for the subcontinent's explosive population growth, new research suggests. The easy-to-manufacture tools - also known as microliths - were a vast improvement over larger stone flake tools used previously, says Michael Petraglia, an archaeologist at the University of Oxford, UK, who led the study. Because microblades could be cut from stone more quickly and in higher volumes than flakes, hunting probably became a vastly more efficient endeavour. "It allows people to more reliably and more cheaply slaughter animals," says Lawrence Guy Straus, a paleoanthropologist at the University of New Mexico in Albuquerque, who was not involved in the study.
     Petraglia and his colleagues contend that the beginnings of a global Ice Age pushed ancient populations of Indians into closer contact - and competition - with one another. "They need to develop new strategies to produce new resources. They invent microlithic technology and it spreads very rapidly." Petraglia's team argue that genetic, environmental and archaeological records make a strong circumstantial case for their theory.
     Between 30 and 35,000 years ago, the Earth cooled dramatically. In India, however, this Ice Age shortened the monsoon season and transformed what had been a rather homogenous tropical landscape into a patchwork of savannahs and deciduous forests bordered by desert, Petraglia says. "When you get more deserts you're getting environmental fragmentation. That is conducive to hunter-gatherers, Petraglia says. These changes almost certainly would have split up ancient populations, but they could have spurred their growth as well, Petraglia says. By treating the mitochondrial DNA of contemporary Indians as a sort of molecular clock, the researchers documented an expansion in Indian genetic diversity dated to around the time of this Ice Age.
     The microblades - narrow and up to 4 centimetres long - began appearing in large numbers around 30,000 years ago, archaeological records from across the subcontinent show. Prior to this, Indians wielded bulkier, less-efficient stone flakes. Microblades, which were probably attached to spears and later arrows, were a game-changing technology that allowed more densely packed hunter-gatherers to thrive, Petraglia says. Later innovations - namely agriculture and livestock domestication - undoubtedly pushed population densities higher. But Petraglia thinks that the shifts that occurred 35,000 years ago got the ball rolling. Its influence can still be seen today, he says. "It's a mystery why there are so many people in that part of the world and it wasn't just domestication that led to more than a billion people being around in South Asia. We argue that is has to go back to a much earlier period."
     Ofer Bar-Yosef, a paleoanthropologist at Harvard University says the discovery of widespread microblade use in India 30,000 years ago "closes an important gap in our knowledge." Similar tools have been found from around this period in Africa, Europe and west Asia. But climate change isn't necessary to spur technological innovation and adoption, Bar-Yosef says. Hominins that predated modern humans wielded stone axes that changed little over hundreds of thousands of years and numerous wild climatic swings.

Source: Scientific American (20 July 2009), NewScientist (21 July 2009)