The Meme Machine

68 THE MEME MACHINE
animals, some different agency was required to explain our consciousness,
morality and spiritual nature, ‘the higher feelings of pure morality’, courageous
self-sacrifice, art, mathematics and philosophy.
Appealing to God or spirits to solve mysteries is no help and few, if any,
scientists now favour Wallace’s ‘solution’. Nevertheless, this old argument
highlights a real problem; our abilities are quite out of line with those of other
living creatures and they do not seem obviously designed for survival.
The gulf is obvious in purely physical measurements (Jerison 1973). The
modern human brain has a volume of about 1350 cubic centimetres (i.e. roughly
three times as large as the brains of existing apes of comparable body size). A
common way of comparing brain sizes is to use the ‘encephalisation quotient’
which compares a given animal’s brain-to-body ratio with the average for a
group of animals. For any group of related animals a plot of brain size against
body size yields a roughly straight line (on a log-log scale). If we humans are
placed on such a line with our closest living relatives we just do not fit. Our
encephalisation quotient compared with other primates is 3. Our brains are far
too large for our bodies.
Of course, the encephalisation quotient is only a crude measure and hides the
different ways in which the body size to brain size ratio can come about. For
example, a chihuahua has a very high encephalisation quotient compared with
that of a Great Dane, but this is because chihuahuas have been specially bred for
small bodies – not for large brains or superior intelligence! So could we have
been selected for small bodies rather than large brains? Deacon (1997), who
pointed out the ‘Chihuahua Fallacy’ explains that the higher encephalisation
quotient of primates compared with other animals is a result of their having
smaller, slower growing bodies. Primates’ brains grow at the same rate as other
species’ but their bodies grow more slowly. However, when you compare
humans with other primates the situation is different. Human fetuses start
growing the same way as other primates’ but then our brains continue to grow
for longer. So our brains do seem to have been selected for extra growth. Our
high encephalisation has come about first from the slowed body growth of
primates and second from the extra brain growth of humans.
When in evolution did this brain growth begin? About five million years ago
the evolutionary branch leading to modern humans split off from that leading to
the present day African apes (Leakey, 1994; Wills 1993). After this, our early
hominid ancestors include various species of australopithecines and