Are all memories created equal? It is virtually certain
that different people have different brain abilities
for different things. One of these differences must
be in memory. But most of the differences in memory
abilities that we see in everyday life do not seem to
be due to differences in the brains we are born with,
but to differences in how well we use the brains we
are born with.
Our brains are probably somewhat like our muscles:
everybody is born with different amounts of muscle.
And this is probably particularly true of the muscle
that is your heart. So it is likely that some people
have bigger, stronger hearts than others do at birth.
But it is also true that many people can take whatever
amount of heart they are born with - large or small—and
train themselves up from couch potato to marathon runner.
The differences we find in everyday memory probably
are comparable. They are probably still mostly based
on how much we exercise what we have, not how much memory
we are born with.
This is not to minimize the fact that different people
may be born with different memory abilities. We know
or suspect that there are genetically-based differences
in brains. Some of the evidence comes from identical
twins. Identical twins are almost exactly alike in their
genetic composition. And identical twins show remarkably
similar intelligence and memory abilities, even when
they have been separated at birth and reared by different
parents, in different environments. They even show remarkably
similar patterns of how those intellectual abilities
develop childhood and adolescence. These similarities
suggest that there is a genetic program for intelligence
and memory, that partly determines the intelligence
and memory that we have in later life.
At the brain level, less is actually known about actual
individual differences in the brain, and even less is
known about individual differences in nerve cell connections.
But these also certainly exist. One known example: an
area of the cortex of the brain - the gray matter -
is the first stop for information coming from the eyes.
This area of the brain is clearly important in vision.
Species with good vision have more of it; species that
lose their vision (such as some that live in caves without
light) lose this brain region. In humans, on the average,
this brain region is three to four times larger than
it is in monkeys - some reflection of our superior brain
power, we would hope. But we also know that in some
people, this area can be three times larger than it
is in other people.