THE ROUGH GUIDE TO PSYCHOLOGYcreated a test of eidetic or “photographic” memory. Human participants
and two chimps watched a computer screen on which numerals were
quickly replaced by blank squares, with their task being to touch the
squares in the correct numerical order. The humans beat the older
of the chimps for accuracy, and both they and she showed a tendency
to become less accurate as the presentation time of the numerals was
decreased. However, the younger chimp, Ayumu, was more accurate
than the humans, and his performance didn’t deteriorate with reduced
presentation-time.
All these demonstrations of surprising feats by animals is all well
and good, but it remains the case that capuchin monkeys don’t author
books, and building cities and cathedrals is beyond even the brainiest
bottle-nosed dolphins. The dividing lines may be fuzzier than they once
were, but the human ability to produce sophisticated inventions – from
written language to the Internet – still puts mankind in a league of its
The human and animal brain compared
From the outside, it’s not immediately obvious what it is about the
human brain that marks us out from the rest of the animal kingdom.
It certainly isn’t sheer size. Whereas a human brain weighs in at about
1.4kg, an elephant brain is over 4kg, whilst the typical sperm whale
boasts a brain of 8 to 9 kilos! What about brain size relative to body
size? This measure paints humans in a more favourable light – we have
one of the biggest brains in the animal kingdom for our body weight.
But still, using this measure, we’re beaten by little animals like squirrels.
Another index is known as the encephalisation quotient, which looks
at expected brain-weight for a species given the taxonomic class it is
in, such as mammal, bird or reptile. By this measure, humans do really
well, having a brain about eight times heavier than you’d expect for a
mammal of our size.
Another distinguishing feature of the human brain that’s often
mentioned is the size of the cerebral cortex. While it’s true that this
structure is particularly large in humans, it’s the organization of the
brain and the way it’s wired up that’s more important. Humans have
more tissue devoted to so-called association cortices than any other
species. These are regions that aren’t dedicated to any one particular
function, but rather to higher-order integration. The human brain is
also more densely packed with brain cells than any other species, with
the result that we have even more neurons than the enormous whale
brain. Finally, the myelin insulation that surrounds some neurons is
thicker in human nervous systems than in other animals, improving
the efficiency of inter-neural communication.