DYNAMICS OF FIELD POPULATION O F PINE LOOPER
301
The second question is concerned with the origin of a mechanism of
this kind. It has been suggested by Wynne-Edwards (1962) that such
mechanisms have evolved by natural selection of social adaptations,
with the result that the disadvantageous effects of over-exploitation of
the environmental resources are avoided. He 13tates that the type of
selection operating at the individual level (i.e. on genotypes within the
population) cannot be effective in eliciting the kind of social adaptations that keep the populations down at the optimum density levels.
Living a t such levels is advantageous for the population and not so
much for the individuals composing the population. Wynne-Edwards
therefore introduces the concept of group-selection, a type of selection
concerned with the viability and survival of the population as a whole.
He does not, however, provide a model or mechanism by means of
which group-selection can be understood to c,xert its differentiating
effect.
The present author meets difficulties in his understanding of the concept, however. The brief formulation of Wynne-Edwards: “ . . . when
the short-term advantage of the individual undermines the future safety
of the race [read “population” in this case], group-selection is bound to
win, because the race will suffer and decline, and be supplanted by
another in which anti-social advancement of the individual is more
rigidly inhibited . . .” in my opinion explains next to nothing.
No more can I appreciate the remarks of Brereton (1962) with reference to this point. He asks: “Can evolution work at the group level?”
and answers: “There is evidence that it can, for how else could behaviour which is disadvantageous to the individual but of advantage to
the group have evolved?” It is questionable in my opinion, however,
whether the cases in which group advantage is ciaid to be involved have
been interpreted correctly. Thus it might well be that, where low population density is considered to be advantageous for the group in avoiding over-exploitation, it is in fact of advantage for the individuals for
some unknown reason to be spread out.
Let us assume, for instance, that in the Bupalus population under
consideration a genotype develops by mutation which is resistant with
respect to the physiological suppression exerted by the other individuals
in the population. This genotype will be at an adivantage and its proportion in the population will gradually increase, with the result that density ultimately surpasses the optimum level. I do not understand how
group-selection is able to prevent such an “anti-social advancement”.
I n my opinion it can be prevented only by being disadvantageous for
the genotype. I n other words, the fact of being immune for mutual
interference must have some disadvantageous effect for its possessor.
How can the advantage of being immune be counteracted by a
r *
301
The second question is concerned with the origin of a mechanism of
this kind. It has been suggested by Wynne-Edwards (1962) that such
mechanisms have evolved by natural selection of social adaptations,
with the result that the disadvantageous effects of over-exploitation of
the environmental resources are avoided. He 13tates that the type of
selection operating at the individual level (i.e. on genotypes within the
population) cannot be effective in eliciting the kind of social adaptations that keep the populations down at the optimum density levels.
Living a t such levels is advantageous for the population and not so
much for the individuals composing the population. Wynne-Edwards
therefore introduces the concept of group-selection, a type of selection
concerned with the viability and survival of the population as a whole.
He does not, however, provide a model or mechanism by means of
which group-selection can be understood to c,xert its differentiating
effect.
The present author meets difficulties in his understanding of the concept, however. The brief formulation of Wynne-Edwards: “ . . . when
the short-term advantage of the individual undermines the future safety
of the race [read “population” in this case], group-selection is bound to
win, because the race will suffer and decline, and be supplanted by
another in which anti-social advancement of the individual is more
rigidly inhibited . . .” in my opinion explains next to nothing.
No more can I appreciate the remarks of Brereton (1962) with reference to this point. He asks: “Can evolution work at the group level?”
and answers: “There is evidence that it can, for how else could behaviour which is disadvantageous to the individual but of advantage to
the group have evolved?” It is questionable in my opinion, however,
whether the cases in which group advantage is ciaid to be involved have
been interpreted correctly. Thus it might well be that, where low population density is considered to be advantageous for the group in avoiding over-exploitation, it is in fact of advantage for the individuals for
some unknown reason to be spread out.
Let us assume, for instance, that in the Bupalus population under
consideration a genotype develops by mutation which is resistant with
respect to the physiological suppression exerted by the other individuals
in the population. This genotype will be at an adivantage and its proportion in the population will gradually increase, with the result that density ultimately surpasses the optimum level. I do not understand how
group-selection is able to prevent such an “anti-social advancement”.
I n my opinion it can be prevented only by being disadvantageous for
the genotype. I n other words, the fact of being immune for mutual
interference must have some disadvantageous effect for its possessor.
How can the advantage of being immune be counteracted by a
r *