42 LISTENER OCTOBER 13 2018
THIS LIFE
GETTY IMAGES
D
umb bunny, stupid cow, bird brain. We do
love to associate lack of intellect with other
animals. I’m not even going to start on how
these terms are more likely to be applied to
women than men.
It seems reasonable to suggest that we use these
descriptors because we perceive animals to be less
intelligent than we homo sapiens. One way in
which we differ from non-human animals is the
size of our brains.
Human brains vary in size. A male brain averages
just over 1250 cubic centimetres, while a female
brain averages just under 1150cu cm. But they can
range in volume from just under 1000 to almost
1400cu cm. An adult brain weighs about 1.25kg.
It’s not entirely silly to obsess about brain size as
a marker of intelligence. In humans, there is a very
small correlation between the size of one’s brain
and one’s score on an intelligence test. This is quite
a contentious discussion, and it’s more complicated
than just “bigger brain equals less stupid”.
We probably don’t want to assume brain size is
the be-all of smarts for another reason. Obviously,
we don’t have the biggest brains around. Sperm
whale brains weigh in around 8kg; dolphin brains
are also bigger than humans at about 1.7kg.
Dolphins are a good example to use, because dol-
phin brain size has been associated with tool use.
If “Flipper” has a bigger brain, she or he is better at
using tools to solve problems. The same is true of
chimpanzees, and tool-using birds such as crows.
There is good reason to think that bigger
brains are an adaptation – in
general, the bigger a brain is,
the more energy it requires
to keep it running, so
there must be a benefit to
having a bigger one.
It’s hard to test this
on humans because of
the necessary timescale
(and the ethical issues), but itThinking big
Brain size may have a
bearing on intelligence,
but there is always a
trade-of.
has been done with guppies – small
fish; quick reproductive cycle; fewer
ethical issues. If you selectively breed
for bigger brains in guppies, you end
up with big-brained guppies who
are better at intelligence tests. I’m
not kidding – you can test fish using
visual tasks to look at relative intel-
ligence. Guppies can count.The downside is that bigger brain
means smaller gut and lower fertil-
ity. It’s a trade-off – if you need to
divert energy to the brain, you need
to take it from somewhere else, and
this is common across species. Bigger
brains mean lower fertility (and a
host of other relative
weaknesses).E
nvironmental
challenges play
a part here, with
implications more
subtle than just overall
brain size. Bats that
use smell to track prey have largerolfactory brain centres than those
that use sound, but their auditory
centres are smaller.
Brain weight relative to body
weight is another way of looking at
this. Elephant brains average about
5kg, but they’re also very heavy
animals, so the ratio of their brain to
body-weight is about 1:600. Wikipe-
dia tells us that the bony-eared assfish
has the smallest known brain- to-
body-mass ratio among animals with
a spine. The ratio for humans is about
1:40, and for small birds about 1:10.
So, back to bird brains. Accord-
ing to University of Auckland senior
lecturer Fabiana Kubke, our national
bird, the kiwi, weighs about 2kg, of
which a minuscule 10g is brain. This
doesn’t seem a good sign for intel-
ligence, but as with all things, this is
relative – it is estimated that long-
extinct moas weighed up to 100kg,
but their brains were a shade over
twice that of a kiwi at 25g. Kiwis win.
The reason for this column was a
chat over coffee with my students.
We have an animal-of-the-week part
of our regular meeting, and Kealagh
tells me that voting for Bird of the
Year is under way (it closes on Octo-
ber 14). To have a say, or check out
the winner, visit birdoftheyear.org.
nz/. lby Marc Wilson
PSYCHOLOGY
Our national bird,
the kiwi, weighs
about 2kg, of which a
minuscule 10g is brain.
Dolphins ofer
evidence that
brain size matters;
the kiwi, below, is
relatively lacking
in grey matter.