Modern Mind

provided the fresh water that made the Mayan civilisation possible. 25 Second, three other mass extinctions are now recognised by palaeontologists, occurring at 365, 250, and 205 million years ago. The disappearance of the dinosaurs also proved to have had a liberating effect on mammals. Until the K/T boundary, mammals were small creatures. This may have helped their survival after the impact – because they were so numerous – but in any event the larger mammals did not emerge until after the K/T, and in the absence of competition from
Tyrannosaurus rex, Triceratops,
and their brothers and sisters. There would probably have been no humans unless the K/T meteorite had collided with Earth.
    So far as the origins of humanity were concerned, the 1980s provided one or two crucial excavations, but the period was really a golden age of interpretation and analysis rather than of discovery.
    ‘Turkana Boy,’ discovered by the Leakeys near Kenya’s Lake Turkana in August 1984, was much taller than people expected and quite slender, the first hominid to approach modern man in his dimensions. 26 He had a narrow spinal canal and a thorax that tapered upward, which suggested to anatomists that Turkana Boy had only limited nerve signals being sent to the thorax, giving him less command of respiration than would have been needed if he were to speak as we do. In other words, Turkana Boy had no language. At the same time the tapered thorax meant that his arms would be closer together, making it easier to hang in trees. Assigning him to
Homo erectus,
the Leakeys dated Turkana Boy to 1.6 million years ago. Two years later their archrival Don Johanson discovered a skeleton at Olduvai, attributed to
Homo habilis
and only 200,000 or so years older. This was very different – short and squat with long arms very like those of an ape. 27 The idea that more than one hominid type was alive at the same time around 2 million years ago was not accepted by all palaeontologists, but it did seem plausible that this was the time when the change occurred that caused hominids to leave the forest. Elisabeth Vrba, from Yale, argued that around 2.5 million years ago other changes induced evolutionary developments. 28 For instance, polar glaciation reduced the temperature of the earth, lowering sea levels and making the climate more arid, reducing vegetation. This was supported by the observation that fossils of forestantelopes become rare at this time, to be replaced by a variety that grazed on dry, open savannahs. 29 Stone tools appeared around 2.5 million years ago, suggesting that hominids left the forests between, say, 2.5 and 1.5 million years ago, growing taller and more graceful in the process, and using primitive tools. More ‘prepared’ tools are seen at about 200,000 years ago, roughly the time when the Neanderthals appeared. Opinions on them changed, too. We now know that their brains were as large as ours, though ‘behind’ the face rather than ‘above’ it. They appeared to bury their dead, decorate their bodies with ochre, and support disabled members of their communities. 30 In other words, they were not the savages the Victorians imagined, and they coexisted with
Homo sapiens
from about 50,000 to 28,000 years ago. 31
    These and other varied finds, between 1975 and 1995, consolidated in Ian Tattersall’s compilation of fossils, therefore suggested the following revised chronology for hominid evolution:
     
4–3 million years ago
Bipedalism
2.5 million years ago
early tool-using
1.5 million years ago
fire (for cooking food, which implies hunting)
1 million years ago
emigration of hominids from Africa
200,000 years ago
more refined tools
 
Neanderthal Man appears
50,000–100,000 years ago
Homo sapiens
appears
28,000 years ago
Neanderthals disappear
     
    And why did the Neanderthals disappear? Many palaeontologists think there can be only one answer:
Homo sapiens
developed the ability to speak. Language gave modern man such an advantage in the competition for food and other resources that his rival was swiftly wiped out.
    There are within cells organelles known as mitochondrial DNA. These organelles lie outside the nucleus and are in effect cell batteries – they produce a substance known as adenosine triphosphate or ATP. In January 1987 in
Nature,
Allan Wilson and Rebecca Cann, from Berkeley, revealed a groundbreaking analysis of mitochondrial DNA used in an archaeological context. The particular property of mitochondrial DNA