Biology Reference
In-Depth Information
(a)
(b)
60
1
50
0.8
40
0.6
30
0.4
20
0.2
10
0
0
0
2
4
6
8
1
2
3
4
5
6
7
8
9
10
11
12 13
14
15 16
17
18
19
Group size
Group size
(c)
30
Females
Males
25
20
15
10
5
0
Juv
SubAd
Year
Adult
Age
Fig. 12.5
Group augmentation in meerkats. In larger groups, (a) individuals spent less time on guard, looking
out for predators and (b) the annual adult mortality rate was lower. From Clutton-Brock
et al
. (1999a, b).
Reprinted with permission from AAAS. (c) Females help more than males, and the help provided by males drops
when they are adults who are about to leave the group. From Clutton-Brock
et al
. (2002). Reprinted with
permission from AAAS. Photo © Andrew Young.
Reciprocity
In an extremely influential paper, Robert Trivers (1971) argued that if individuals
preferentially help those that have helped them (reciprocal helping), then any short-term
cost of helping another individual can be more than repaid by the help that is returned
in exchange at a later point. For example, A helps B today and then B helps A tomorrow,
as encapsulated by the well-known phrase 'you scratch my back and I'll scratch yours'.
The problem for the evolution of reciprocity is the possibility of free riding. Because of
the time delay between one individual gaining and the other doing so, B may accept help
Paying back a
favour in the
future …
