But this changed between 60,000 and 40,000 years ago, when some groups of humans developed modifications in their tongue and vocal tract. This granted them a finer control of the larynx and made them capable of creating a great variety of sounds and develop a large vocabulary. In his book The Third Chimpanzee: The Evolution and Future of the Human Animal, (Chapter 2, “The Great Leap Forward”), Diamond writes:
“It is easy to appreciate how a tiny change in anatomy resulting in capacity for speech would produce a huge change in behaviour. With language, it takes only a few seconds to communicate the message, 'Turn sharp right at the fourth tree and drive the male antelope towards the reddish boulder, where I'll hide to spear it.' Without language, that message could be communicated only with difficulty, if at all. Without language, two proto-humans could not brainstorm together about how to devise a better tool, or about what a cave painting might mean. Without language, even one proto-human would have had difficulty thinking out for himself or herself how to devise a better tool.”
However, the great leap forward did not happen as soon as the mutations for altered tongue and larynx anatomy arose. Diamond says that it must have taken the humans thousands of years to develop something resembling modern language — a language that has the concept of meaning, rules of grammar, and a sufficiently large number of words. The human groups that developed the biological capacity for language became more advanced than the other creatures—for instance, with their advanced linguistic skills some groups of Cro-Magnon man were far ahead of the Neanderthals.
Diamond notes that if the Cro-Magnon man were transported to modern settings and provided modern education and training, he could fly an airplane. Here’s an excerpt from Chapter 2, “The Great Leap Forward”:
“I have argued that we were fully modern in anatomy and behaviour and language by 40,000 years ago, and that a Cro-Magnon could have been taught to fly a jet aeroplane. If so, why did it take so long after the Great Leap Forward for us to invent writing and build the Parthenon? The answer may be similar to the explanation why the Romans, great engineers that they were, didn't build atomic bombs. To reach the point of building an A-bomb required two thousand years of technological advances beyond Roman levels, such as the invention of gunpowder and calculus, the development of atomic theory, and the isolation of uranium. Similarly, writing and the Parthenon depended on tens of thousands of years of cumulative developments after the arrival of Cro-Magnons — developments that included the bow and arrow, pottery, domestication of plants and animals, and many others.
“Until the Great Leap Forward, human culture had developed at a snail's pace for millions of years. That pace was dictated by the slow rate of genetic change. After the Leap, cultural development no longer depended on genetic change. Despite negligible changes in our anatomy, there has been far more cultural evolution in the past 40,000 years than in the millions of years before.”