... I would think that put that way, it is obvious that group selection exists; groups die out differently, split up at different speed, send propagules at
Message 1 of 13
, Sep 2, 2005
The four different questions I
The replicator question: Which entity passes on its structure directly in
(usually, but not always, the gene).
The interactor question: Which entities are being directly selected at a
given level such that
replication is differential?
The beneficiary question: Which entity benefits, in the long run, from
The manifestor-of-adaptation question: which entity at a given level of
manifests an engineering adaptation?
This taxonomy also disentangles the very long-running battle between John
Smith and the American group selectionists, Michael Wade and DS
Wilson. This is one
reason JMS liked it. Maynard Smith had always defined group
selection as a
*combination*: group selection occurred when groups were interactors AND
of a group-level adaptation (i.e., an individual self-sacrificial
trait). But this isn't a proper
definition of group selection, in that it isn't parallel to the
definition of organismic
selection, and it wasn't the one that Wade and Wilson were using.
Wade and Wilson were
using a *simple*, one-part definition of group selection: group selection
groups were interactors. Full stop.
I would think that put that way, it is obvious that group selection
exists; groups die out differently, split up at different speed, send
propagules at different speed, etc, then group selection exists
necessarily. The same for species, the same for individuals. The
interesting question is what bearing this has in the evolution of
adaptation? Can group adaptations evolve because of group selection? All
group selectionists (Wynne-Edwards, Wade, Wilson, Sober) say the answer
is yes - and the most discussed example of group adaptation is
self-sacrifice by a group member. Then, calling group selectionists to
those that just believe that groups die and reproduce differently implies
that *everybody* is a group selectionist.
Maynard Smith could never disagree that group selection exists; his
disagreement was on the importance of it to evolution, and especially to
the evolution of group adaptations. He doubted that it was an important
force, because D. S. Wilson model needs: i) That groups have important
genetic differences, and there is group heritability; ii) That these
differences are strongly correlated with the survival of the groups; iii)
That migration between groups is low; iv) That within group genetic
variation is low.
In parasites infecting hosts, the above mentioned factors seem more
likely true - hosts are "islands" more than
"villages", isolation is strong. Then, I think there is a
consensus that group selection (called "between host selection"
in the trade) is what counts more for adaptation of parasites. Parasitic
adaptation is more likely to promote the success of the whole bunch (and
there is mounting evidence that it does, for example, *some* cholera
bacteria promote host diarrhea through a toxin, which helps the group as
a whole, even non-toxin producing bacteria). However, even in this
context, the concept of group selection was attacked: Alexander &
Borgia, in their 1978 paper said these cases are better understood in the
realm of "superorganisms" - that is, the bunch of parasites is
a superorganism, with division of labour, as in social insects, or the
cells of a vertebrate, so between host selection can be usefully
described as *individual selection* and not group selection. Responding
to this, Sober & Wilson (1998) complained that many people are doing
whatever they can to dismiss group selection!
Alexander, R.D. and Borgia, G. (1978) Group selection, altruism and the
levels of organization of life. Ann. Rev. Ecology Systematics 9,
Sober, E. & Wilson, D. S. (1998) Unto Others the Evolution and
Psychology of Unselfish Behavior, Cambridge MA: Harvard University
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