I like this kind of question because it lets me
talk about the way that a structure is related
to its function. Let’s start with the brain
The size of the brain by itself doesn’t say a
lot. A better predictor of intelligence is the
ratio of brain size to body size. Say you
were making a bunch of sandwiches and had to
figure out whether you could spread the peanut
butter pretty thick. Knowing the size of the PB
jar is not enough, you have to know how many
slices of bread you’re covering. That would be the
ratio of PB to bread.
Bigger animals need bigger brains just to get the
incoming information from a bigger body and
control its movements. What we really want to know
is whether the brain is larger than you would
predict if you just knew the body size. Hippos
have a pretty big brain, but their brain makes up
roughly 1/2800 of their body weight. Our brain
makes up about 1/40 of our body weight.
Dolphins are close to us with a ratio of
1/50. This isn’t quite the whole story for a
couple of reasons. First, there’s apparently a
minimum size for a mammal’s brain. Then as body
size increases, brain size increases more slowly.
This means that the ratio of a mouse’s brain to
its body is similar to ours, even though mice
aren’t capable of the same kind of problem solving
that dolphins are. Researchers use a
mathematical equation to correct for this and get
something called an encephilization
quotient. “Cephala” means head. Let’s just
call it an EQ. We’re way up there on the EQ
sale with a score of 7.44, while dolphins are a
5.31. That’s still really high. Mice are down
there a 0.5, but they’re still above the rabbits,
which are at 0.4.
But there’s more. The part of a mammal’s brain
that does the real thinking and reasoning is the
outer layer. Now we have to talk about
shape. Imagine that I challenged you to put an
entire sheet of notebook paper between your thumb
and forefinger. One edge of the paper has to
touch each side. Pretty soon you’d probably
realize that you could fold the paper like an
accordion, something like this: WWWWW.
Folding is how you fit something with a big
surface area into a small container. The
surface of our brain looks all folded up because
we have a whole lot of that thinking surface layer
packed into our skulls. Dolphin brains are
wrinkly too. Check out this site for a
compare brain size . The brain of a
rabbit is pretty smooth. Sorry rabbits.
Of course, we also have evidence from
dolphin behavior that they are quite
intelligent. They can learn many tasks,
understand many signals, and even solve problems.
There is evidence that they recognize themselves
in mirrors, which is an important test because it
suggests self-awareness. Other animals just
react to their mirror image as another animal at
first, then ignore it.
It’s difficult to directly compare intelligence
across species. Dolphins aren’t good at tying
knots, but we can’t catch fish with our mouths. We
can do algebra. They can echolocate. It’s
sort of like trying to say whether a rugby player
is a better athlete than a basketball player. It
makes more sense to appreciate both for the skills
Some people have suggested that dolphins are
intelligent because they live in complex social
groups. How do you think that living in a
social group might require a big brain?
Thanks for asking.
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