A CRIMINAL HISTORY OF MANKIND

after this, there emerged another form of man with a still larger brain - about 700 cc - and who used
primitive flint tools. He has been labelled homo habilis. And he, like Australopithecus, was active
during an epoch of unprecedentedly bad weather - droughts, floods, ice ages - called the
Pleistocene, which began about two million years ago. No one knows quite what caused the
Pleistocene. The most popular theory is that polar ice reached such proportions that it began to split
apart under its own pressure and giant icebergs floated towards the equator. But from man’s point
of view, the ice and floods of the Pleistocene were infinitely preferable to the long drought - in
Africa, almost twelve million years long - of the Pliocene. This was the period when man suddenly
put on an evolutionary spurt and began to outdistance every other animal on the face of the earth,
including his cousin the ape. And during the next million years there emerged the creature who
murdered his prisoners in the caves at Chou-kou-tien: homo erectus. His brain was about twice as
big as that of Australopithecus - which makes it about two-thirds the size of that of modern man.
We know that he used fire, although he did not know how to make it; and this itself argues a highly
evolved social life. It implies that when hunters came upon a tree that had been set on fire by
lightning, they carefully carried away burning branches and then appointed guardians to keep it
permanently alight. Man was learning to think ahead, and had therefore outpaced every other living
animal. From the fact that only skulls were found in the Chou-kou-tien caves, we may speculate
that homo erectus was a head hunter, and that therefore his capacity for violence was already well
developed.
And still the human brain went on expanding. In the half million years between Peking man and
ourselves, it grew by another third, and most of that growth was in its top layer, the cerebrum - the
part with which we think. No one knows quite why it expanded so fast. Ardrey even suggests the
fascinating notion that it may have been connected with a huge meteor - or perhaps a small asteroid
- that exploded over the Indian Ocean about 700,000 years ago. Its fragments - known as tektites -
can still be found scattered over more than twenty million square miles. At the same time, the
earth’s poles reversed, so that south became north and vice versa. No geologist can yet explain why
this happened - or why it has happened on a number of previous occasions in the earth’s history. At
all events, Ardrey suggests that the explosion, or the reversal of the earth’s polarity, or both,
somehow triggered the ‘brain explosion’. During the reversal period, the planet would be
temporarily without a magnetic field, and the result could be that earth experienced a sudden heavy
bombardment of cosmic rays and other high-speed particles of the kind that are at present diverted
by the Van Allen belts around us. There would also be a sudden rise in the temperature of the
earth’s atmosphere. Both these factors could cause genetic mutations which might be responsible
for the ‘brain explosion’. On the other hand, this ‘catastrophe theory’ may be unnecessary. If man’s
brain had already doubled in size between Australopithecus and the first homo erectus about a
million years later, then there is nothing very startling in a further increase of about a third in
another half million years.
There is, however, one outstanding mystery. Peking man already had a brain that was far bigger
than that of Australopithecus; in fact, some of the larger-brained Peking men had brains as big as
some smaller-brained modern men. What did he do with it? He certainly learned to build himself
crude shelters made of branches, and developed more elaborate hunting techniques - he had even
learned to kill elephants. Yet his tools made practically no advance. A mere 300,000 years ago,
homo erectus was still using the crude flint choppers that homo habilis had been using two million
years ago. And so things continued down to the time of Neanderthal man, who appeared on the
scene only about a hundred thousand years ago. He was still a thoroughly ape-like creature with a
receding chin and receding forehead, and his cave-dwellings indicate that he was also a cannibal.