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The reading passage introduces three
theories to explain the reasons why the size of human brain has been shrinking.
On the other hand, the lecturer casts doubt on these explanations by mentioning
that they are not very satisfactory.
First, the reading passage contends that a decline
in the size of human society and the following specialized work division made
human brains smaller. However, the lecturer refutes this argument by arguing
that the change in the group size did not decrease demands for the mental capacity.
This rather necessitates new kinds of intelligence such as social intelligence.
For instance, humans are required to develop a complicate function in their
brains to maintain social relationships.
Next, the reading passage maintains that human
brains have has shrunk as a response to the decreased human body size. On the
contrary, the lecturer counters this claim by pointing out that a declining
rate of brain size is much faster than the one of body size. To be specific,
while the brain volume has shrunk at the rate of 16%, the body volume has
shrunk at the rate of 8%. The lecturer goes on to say that if the change in the
body size was accountable for the change in the brain size, their rates would
be similar.
Finally, the reading passage claims that a decreased
necessity for sharp visual capacity made visual cortex in brain to shrink shrunk due to
the lifestyle change, causing brain size to become smaller as a consequence. On
the other hand, the lecturer contradicts this assertion by stating that it is not
the primary reason for the shift of the brain size. This is because visual cortex
occupies smallest space in the brain, which has little impact on the overall
size change in the brain. Furthermore, other parts that occupy more space have
shrunk as well. |