ESS newsletter, October 1996
IN
DEFENCE OF GROUP SELECTIONISM
It saddens me to read that I cannot be both a sociobiologist and a group selectionist
(Roes, 1996). I like to think that I am
both. At least, I like to think that as
a sociobiologist I have the right to consider the
possibilities of selection at all levels.
I would like to try to further the debate by giving an example, and I
will choose a purely theoretical example which is also non-emotive, so that we
are not affected by the emotions which surround the selection of altruistic
traits.
A fishy example
Let us imagine a schooling fish which is preyed
on by two predators. The big predator
eats whole schools of fish in one gulp, and is not interested in a few
individuals who stray from the group.
The little predator cannot take on a whole school, but tends to
concentrate on individuals who stray from the school. Already we can say that in the evolutionary
history of this species the little predator has been more important, otherwise
the fish would not school, and in so doing bundle themselves into convenient
mouthfuls for the big predator.
Let us also imagine that one of the predator
avoidance strategies of this fish is to turn to the left or right when it
senses a predator in front of it. It
does not swim straight on into the predators
mouth. Any fish that did that in the
past have not lived to reproduce. The
fish has to decide whether to turn to the left or the right when it senses a
predator in front. The choice of left or
right could be determined in a number of ways, such as by randomisation, or by
doing the opposite of what it did last time, or by sensing a slight deviation
of the predator from the mid-line. All
these methods have disadvantages, especially for a schooling fish. For instance, slight deviations from the
midline might give opposite decisions in different members of the school who
might have slightly different orientations in space, and also some fish might
be paralysed by being unable to make a decision, and get into the condition of
Pavlov's dogs asked to distinguish between a circle and a nearly circular
ellipse.
Therefore we have the right to imagine that the
choice between left and right is genetically determined, and it does not matter
for our argument whether the genetic variation is monogenetic or multifactorial.
There are left-turning fish and right-turning fish, and the difference
is heritable.
Let us imagine the situation in a habitat which
is dominated by the small predator. Fish
which do not turn with the school are at a disadvantage. Therefore, the rarer the
genotype, the less its payoff. We
are in a situation of positive frequency-dependent selection. The most frequent allele will increase in
frequency until it becomes fixed. There
is no intrinsic advantage in turning left or right, only in turning the same
way as the others. Therefore, if there
is not much genetic exchange between schools of fish, some schools will become
fixed as left-turners, whereas other schools will become fixed as right-turners. There will be a lot of between-school
variation but not much within-school variation.
Enter the large predator. His success in devouring a whole school of
fish depends on predicting which way it will turn when he approaches it. If he is in a habitat of largely
right-turning schools, he will assume the school will turn to the right, and
therefore a left-turning school is more likely to escape him. Here we are in a situation of negative
frequency-dependent selection.
School-wise, it pays to be unlike the other schools. Therefore the variation between the schools
will be maintained. Neither type of
school can die out, because the less frequent it gets, the more it is likely to
survive.
The overall situation is one in which genetic
homogeneity within schools is maintained by positive frequency-dependent
selection, whereas genetic heterogeneity between schools is maintained by
negative frequency=dependent selection.
In order to understand the population dynamics of our fish, should we
not consider selection both at the level of the school and at the level of the
individual fish?
Has the expression of anti-group selectionist sentiment become a badge of biological
respectability?
During the thirty odd years of my professional
life, there has been a prejudice against group selection talk. I am sure that in biology generally, people
who talked favourably about group selection did not get jobs, and lost respect
from their peers. There was what might
be called positive frequency-dependent social selection, because the more
anti-group selectionists in the scientific
establishment, the more it paid to be anti-group-selectionist. It could have gone the other way. Wynne-Edwards could have won the intellectual
battle with his powerful book (Wynne-Edwards, 1962), and it could have become
beyond the Pale to be a selfish genist. Then the population of scientific
establishments could have become fixed as pro-group selectionist. Now that pro-group selectionist
material is beginning to appear in print again (Wilson and Sober, 1994; Eibl-Eibesfeldt, 1982 and 1995;
Bloom, 1995; Stevens and Price,
1996; Price and Stevens, in press) we
are in some danger of splitting into two opposing camps.
Should
we not, as sociobiologists, recognise that we are
dealing with a group process which has the effect of causing homogeneity within
groups and emphasising differences between groups? As scientists, should we not be in favour of
heterogeneity, both within and between groups?
Literature
Bloom, H. (1995) The
Lucifer Principle: A Scientific Expedition into the Forces of History.
Eibl-Eibesfeldt,
Eibl-Eibesfeldt,
Price, J.S. and Stevens, A. (in press) The group-splitting hypothesis of schizophrenia. In The Evolution of the
Psyche (ed. D.Rosen, R.Gardner & M.Luebbert).
Roes, F. (1996) Against group-selectionism. European Sociobiological
Society Newsletter, Number 41, April, 3-7.
Stevens, A. & Price, J. (1996) Evolutionary
Psychiatry: A New Beginning.
Wilson, D.S. & Sober, E. (1994)
Reintroducing group selection to the human behavioral
sciences. Behavioral
and Brain Sciences, 17, 585-608 (open peer commentary 608-654).
Wynne-Edwards, V.C.
(1962) Animal Dispersion in Relation to Social Behaviour.
John Price