Evolution__3rd_Edition

..
Kin selection is at work in this
example
Some adaptations may benefit the
group, but not the individual ...
. . . such as reproductive restraint
and its parents’ a and we have to weigh each kind by the chance they share a gene with
the helper.)
For the two methods of estimating cost, the inequalities are approximately:
Lower bound estimate: 1 /2 × 14 > 1 /2 × 0
Higher bound estimate: 1 /2 × 14 > 1 /2 × 7
CHAPTER 11 / The Units of Selection 301
Either way, natural selection favors helping behavior in young Florida scrub jays. The
estimates of both b and c are fallible, however, and the test is uncertain. Despite these
uncertainties, the test does illustrate how we can attempt a quantitative test of the
theory of kin selection.
11.2.5 Whether group selection ever produces adaptations for the
benefit of groups has been controversial, though most biologists
now think it is only a weak force in evolution
A group adaptation is a property of a group of organisms that benefits the survival and
reproduction of the group as a whole. Adaptations produced by kin selection a such as
helping in family groups of birds a will satisfy that definition, but we are concerned
here with group adaptations that did not evolve by kin selection. If any exist, they will
have come into existence by selection between groups: groups possessing the group
adaptation would have gone extinct at a lower rate, and sent out more emigrants, than
groups lacking it. The group adaptation would have been favored by the differential
reproduction of whole groups.
Many characters are beneficial at the group level, but also benefit all the individuals
in the group. This would trivially be true, for example, of an improvement in the hunting
skill of a lion: after the improvement has spread by individual selection, all the individuals
in the group, and the group as a whole, will be better adapted. That is just to
restate the earlier point that adaptations that have evolved for the benefit of one level of
organization can incidentally benefit higher levels. The controversial group adaptations
are those that benefit the group but not the individual. A hypothetical example is
Wynne-Edwards theory, put forward in Animal Dispersion in Relation to Social
Behaviour (1962), that animals restrain their reproduction in order not to overeat the
local food supply. If all the individuals in a group reproduce at the maximum rate, their
offspring might overeat the food supply, and the group would then go extinct. They
could avoid this fate by collectively restraining their reproduction, to maintain the balance
of nature. Natural selection on individuals does not favor reproductive restraint.
An individual that increases its reproduction will automatically be favored relative to
individuals that produce fewer offspring. Within a group, if some individuals produce
more offspring than others, the former will proliferate. But can individual selection
within the group be overcome by selection between groups?
The question is highly important, both conceptually and historically. It is important
historically because vague group selectionist thinking a particularly in the form of
statements like “adaptation X exists for the good of the species” a was once common. It
is now more usual (though by no means universal) for biologists to believe that group