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Psychology unit 3 intelligence revision
Evolution of human intelligence- brain size
Fossil evidence has shown that the brain size has tripled over the past 5 million
years from being 500cm3 to 1500cm3. This suggests there's a link between brain
size and intelligence because modern humans are more intelligent than early
For modern humans there is a correlation between brain size and IQ. This has a
positive correlation of +0.4. However this is a weak correlation which suggests
that there are other factors influencing intelligence. If this was the only factor
the correlation would be +0.1.
Body size can impact brain size. A larger animal will have a larger brain, however
larger animals aren't always more intelligent than smaller animals. For example,
elephants have larger brains and bodies than humans but there are less intelligent.
This suggests other factors influence intelligence.
The ratio of brain to body size is called the encephalisation quotient which is
brain size divided by body size. This has found that humans have a brain 3 times
bigger than it should be. A chimpanzee has a similar body size to humans but they
are less intelligent. This means it could be that humans are more intelligent for
A problem with comparing brain sizes is that it doesn't take into account the
different functions of the brain. Only the frontal lobes involved in intelligence so
when looking at the evolution of intelligence we should be looking at the evolution
of the frontal lobe, and not the whole brain. Humans have the largest frontal lobe
and are the most intelligent, suggesting the two are linked.
Having larger brains means parental responsibility of a child is greater. This
means parents can't evolve intelligence as well as there is less time to hunt if
caring for a child.
20% of bodily energy intake is used by the brain so having bigger brains means
more food is needed so more energy has to be used and time would have to be put
In order to counteract these two limitations and make big brains possible,
intelligence must have evolved.