Biology Reference
In-Depth Information
is that cooperation is favoured with group members because they will usually be close
relatives (i.e. indirect benefits by limited dispersal; Foster, 2004). This possibility is
emphasized by the fact that only five of the 98 observations of sharing between
individuals of known genetic relatedness involved individuals less related than
grandparent to grandchild (r < 0.25). Another possibility is that begging may
represent a form of harassment that prevents well fed individuals settling into torpor
for the day's rest, in which case feeding could be favoured for the direct benefit of
reducing harassment. A final possibility is that there can be a direct benefit to keeping
other individuals in the same group alive. For example, keeping other group members
alive would increase the number of individuals that could be begged from in the
future, providing a direct benefit analogous to group augmentation. Whilst this
involves helping individuals because help could be obtained from them in the future,
it does not rely upon preferentially directing help towards more helpful individuals.
… and simpler
explanations are
possible based on
kin selection and
by-product
benefits.
Food and mate sharing in primates
Craig Packer (1977) studied a possible example of reciprocity in the olive baboon,
Papio
anubis
. When a female comes into oestrus a male forms a consort relationship with her,
following her around wherever she goes, awaiting the opportunity to mate. Sometimes
pairs of males use identifiable signals to form coalitions to attack competitors that are
consorting receptive females. This frequently led to the solicited male engaging the
consort male in a fight and, while they are busy doing battle, the male who enlisted help
goes off with the female! This was argued to be reciprocity, on the grounds that on a later
occasion the roles are reversed, with the male who gave help being assisted by the one
who received help previously. However, there is little evidence that individuals are more
likely to 'allow' the other male to mate the female, if they have helped them in the past
(condition 3 above). Furthermore, more recent observations suggests that after females
have been 'liberated' from their previous consorts, both partners run for the female and
do their best to monopolize her (Bercovitch, 1988), suggesting that cooperation can be
explained more simply by the immediate direct benefits (condition 4) - forming a pair
leads to an increased probability of mating with the female.
Another commonly cited example of reciprocity is the sharing of meat between
male chimpanzees. Male chimpanzees hunt in groups for small and medium sized
mammals, such as monkeys and small pigs. After a successful hunt, individuals will
surround whichever animal has the prey item, begging for food. It is often argued that
this represents a form of reciprocity, where individuals preferentially exchange meat
with allies. However, more detailed studies have shown little evidence that individuals
preferentially give meat to those that have fed them previously (condition 3). Instead,
the probability that meat is shared is mainly dependent upon the amount of
harassment that is received from beggars (Gilby, 2006), suggesting that cooperation
is more simply explained as a mechanism to reduce harassment (condition 4).
Male olive
baboons pair up
to compete for
females
Chimpanzees
share meat
Enforcement
Our discussion of reciprocity considered how cooperation could be favoured between
individuals who preferentially help each other ('help those that help you'). Whilst this
may be relatively unimportant, there are many other ways to enforce cooperation,
