The Meme Machine

198 THE MEME MACHINE
the species’ without any idea of possible mechanisms. Williams’s classic book
Adaptation and Natural Selection (1966) pointed out the errors: for example,
that selfish individuals could always infiltrate altruistic groups and thrive at their
expense. Also groups have a slow lifecycle compared with individuals, and
individuals can often move between groups. This means that individual
adaptations will almost always predominate over adaptations for the group.
Therefore, we should not look to group selection as a force that can make
individuals sacrifice their own genetic interests for the ‘good of the group’.
Most biologists now consider that group selection is only a weak force in
nature (Mark Ridley 1996). However, selection at the level of the group can
sometimes occur. Dawkins’s distinction between the replicator and the vehicle
is helpful here. In most of biology the replicator (the thing that gets copied) is
the gene, while the vehicle is the whole organism. Whole organisms; that is
individual cats, donkeys, orchids or cockroaches, live or die, and in the process
either pass on their genes or not. All the genes in that vehicle share the same
fate. In this (the most common) case selection is taking place at the level of the
organism.
In some cases, however, whole groups of organisms live or die, and so all the
genes in the group are killed off at once. If this occurs then the group is the
vehicle and we can say that selection is happening at the level of the group. This
applies, for example, to whole species that go extinct, or to isolated populations
of animals, such as those on small islands, in which some groups survive and
some do not. In these cases there is no conflict between individual and group
selection (as there was in the argument about altruistic behaviour) but selection
has acted at the level of the group.
Ridley (1996) concludes that group selection works only if migration rates
are implausibly low and group extinction rates implausibly high. Another way
of putting it is that group selection is favoured by mechanisms that reduce the
differences in biological fitness within the groups and increase differences
between groups, thus concentrating selection at the group level (D. S. Wilson
and Sober 1994).
Memes may provide just this kind of mechanism. Indeed Boyd and
Richerson (1990) have used mathematical models to show that group selection is
particularly likely to occur when behavioural variation is culturally acquired,
and that it can even occur with large groups and substantial rates of migration.
The important point is that memes can have precisely the effect of decreasing
within-group differences and increasing between-group differences.