168 Unit 4 Applied critical thinking
large groups, spend much less time grooming
than baboons, which form groups of 50 or
more. Of course, two favourable examples do
not prove the theory correct, or even give it
much support. Doc D, on the other hand,
provides many such examples. And, as in Doc
B, the trend does support the hypothesis: time
spent grooming does show a tendency to
increase with group size. There are a few
‘outliers’, as they are called: one species which
grooms more than most but has a group size of
around 10; and the primate with the second-
largest group size grooms less than many
which live in smaller groups. (These are
‘outliers’ because the points on the graphs lie
furthest from the centre of the bunch.) You
can single out for yourself other examples
which are not typical. The question you must
ask is whether these anomalies are enough to
discredit the theory, or whether they can be
ignored, or explained (see Chapter 4.2,
pages 140–1).
You might also have picked up on the fact
which Professor Dunbar makes at the end of
the first paragraph of Doc B: ‘As group size and
time spent grooming increases, this social
effort is concentrated on fewer and fewer
partners.’ This may seem puzzling. It may even
seem to contradict the main idea that group
size goes with more grooming. For both
reasons, it calls out for an explanation, which
takes us on to our next and final question.4 What explanation could be given for the
fact that in large groups grooming is
concentrated on fewer partners?Activity
Commentary
There may be a number of plausible
explanations which you could give, so do not
be concerned if your answer is different from
the one here. It is a suggested answer, not the3 In the first sentence of Doc B, the author
claims that monkeys and apes develop
social relations by grooming each other.
How well does the rest of the document,
and the information in the second graph
(Doc D), support this claim?Activity
Commentary
Firstly the author explains how grooming may
account for the building of relationships
within a group. It is known that naturally
produced chemicals called endorphins can
cause a pleasurable (euphoric) feeling in
humans. We know that among the ‘triggers’
which release endorphins is massage, which is
very similar to grooming. Laughter, music-
making and so on have similar effects. If
people share these pleasurable experiences it
tends to bind them together as friends or
partners. It is a plausible hypothesis that
grooming has a similar effect among animals,
and results in bonding between individuals
within the group.
As we have seen several times in previous
chapters, being plausible is not enough to
make a hypothesis true. But it is enough to
make it worth investigating further. This
brings us to one of the key features of scientific
reasoning: the need to test hypotheses by
looking for further evidence which either
corroborates or disproves it. The methodology
is this: we suppose that the hypothesis is
correct and ask ourselves what else would be
true or probable as a consequence. In this case
the question would be: If the grooming theory
is right, what else would we expect to find?
One quite obvious expectation would be
that animals with large social groups would do
more grooming than those which form very
small groups. In Doc B Professor Dunbar
provides some data which suggests that this is
indeed the case: gibbons, which don’t form