Wednesday, 7 March 2012

Pollock on Wynne-Edwards [updated]

Gregory B. Pollock (1989, p. 205) construed the criticism against Wynne-Edwards as follows:
Critique of Wynne-Edwards’ view on population regulation and sociality suppose a population of discrete, mutually exclusive groups essential to his thought. Yet both his past and present work focus on continually distributed, philopartric populations; his critics have argued the untenability of a position never his own.”
As I understood the criticism of Maynard Smith (1964), he did not claim that Wynne-Edwards (1962, 1963) assumed strict isolation of breeding groups, but that the sort of group selection he supposed would require such isolation in order to prevent cheats from undermining the group benefit.* 

     One frequently repeated criticism against Maynard Smith (1964) is that his haystack model was biased against group selection: 
While the model was admittedly extreme, it became the sine qua non of group selection for many [citations omitted]. Groups were assigned the same indivisible integrity as individuals. Conjectured group advantageous traits such as altruism (i. e., foregoing some degree of personal reproduction to aid others) were, by definition, expressed homogeneously within groups; intra-group heterogeneity was always eliminated through intra-group selection [citations omitted]. The appearance of a single mutant cheater, foregoing altruism for an immediate reproductive advantage in its group, then necessarily converts a group into a collection of selfish individuals. Group selection would require that groups with cheaters be eliminated as fast as they appear; that is, that the rate of group extinction is identical to the individual mutation rate for cheating, a not quite absurd possibility in nature [citation omitted]. (Pollock 1989, p. 207)
Though Maynard Smith (1964, p. 110) admits that his model is greatly oversimplifiedthe passages before the model suggest that he tried to bias it towards what he thought would favour group selection. He lists the conditions supposedly necessary for group selection as:
“(1) Groups must for a time be reproductively isolated, because a is eliminated from mixed groups.” [Where a is a genotype refraining from breeding at high population density.]
(2) Groups must be started by one or a few founders, since otherwise groups consisting entirely of a individuals would never come into existence.
(3) When a group of A individuals outstrips its food supply, it must not immediately encroach on the food supply of neighboring a groups, for if it did so, the advantage of a groups would disappear.” (Maynard Smith 1964, p. 109f)
The Haystack model assumes mice breeding in haystacks, breeding groups being established by single fertilized females, and haystacks being isolated from migration for a breeding season. That's just an implementation of the above assumptions. 
      Wynne-Edwards’s scenario lacked, as far as I can tell, a mechanism to prevent cheats from undermining the group benefit. Clarifying such mechanisms were later contributions to multilevel selection theory associated with David Sloan Wilson and others. 
      Now, there are the opposing claims that (1.) Wynne-Edwards was wrong because he did not provide a mechanism against cheats, and that (2.) the critics were wrong because later research showed that such mechanisms were possible after all. 
     Given that Maynard Smith's (1964) criticism was retrospective in so far as he already was in the know of Hamilton's seminal publication on social behaviour and inclusive fitness theory, the above opposition seems to amount to a choice between two Whiggish alternatives. Either retrospectively falsify or vindicate Wynne-Edwards. The falsification is based on a distinction between group and kin selection that Wynne-Edwards did/could not make. And the vindication would be based on still later distinctions of different models of multilevel selection that Maynard Smith did/could not make. 

* I do not deal with the criticism of Williams (1966, p. 92-124), here, because it is a piece of advocacy against group selection mixing arguments of simplicity (Occham's razor), just-so stories for individual selection, new terms (organic vs. biotic adaptation), fossil evidence for species selection (differential extinction), and general ideas about the practical irrelevance of group selection. As Williams (1966, p. vi) states himself: “Reasons are advanced for doubting, a priori, the effectiveness of such group selection.”

P.S.: Other posts on this blog concerning the history of the group selection controversy are:
Wright (1945) on group selection  
Hamilton on group/kin selection  
Darwin on group/kin selection  
What did Wynne-Edwards (1962) actually propose?
Wynne-Edwards regarded groups as a third level of selection - not second


References
Maynard Smith J (1964) Group selection and kin selection: a rejoinder. Nature 201: 1145-1147. [reprinted in Williams (1971) Group selection. Aldine Transactions]
Pollock GB (1989) Suspending disbelief—of Wynne-Edwards and his reception. J. Evol. Biol. 2: 205-221.
Williams GC (1966/1996) Adaptation and natural selection. Princeton University Press.
Wynne-Edwards VC (1962) Animal dispersion. Oliver and Boyd, Edinburgh.
Wynne-Edwards VC (1963) Intergroup selection in the evolution of social systems. Nature 200: 623-626. [reprinted in Williams (1971) Group selection. Aldine Transactions]

No comments:

Post a Comment