Joined: May 2006
I've been thinking about doing this for a while now, and considering I'm working on a new course curriculum for a course in evolutionary biology from a history of prediction standpoint, I thought it would be worthwhile to set up a thread as a repository of information and discussion on the history and current debate surrounding multi-level selection models.
Typically, this boils down to the debate over what level selection acts at: gene, individual, group, population, species, or some combination of the above.
I'm going to keep the introduction to this topic short, as I really want the tread to become more of a repository of specific studies that examine the practical application of multi-level (or purely group) selection models, which those interested can discuss in detail at leisure. So, I'm just going to very briefly touch on some of the history, and then go right into listing some references, and encourage others to post relevant references they run across, with commentary as they see fit. As time permits, we can discuss specifics of some of the papers, and maybe come to some resolution as to the actual efficacy of some of the models that go beyond individual selection. pardon the quick and dirty generalizations, and my leaving out players that are/were also important in the debate.
Because selection must act on phenotypes, and those phenotypes typically must be heritable for evolution to proceed via selection, it is natural that the early models developed by Fisher in the 1930's were based on the idea that selection operates at the level of the individual.
the idea of group selection in the "modern" era was basically introduced by Wynn-Edwards in the early 1960's, but the introduction of game theory and its application by Maynard Smith also in the 60's (think: cheaters) tended to invalidate the concept of selection acting on groups, as any group behavior would be subject to individual cheaters.
Moreover, the explanation of specific behaviors such as those typically considered 'altruistic' also were considered hurdles to the idea of individual selection. However, with the introduction of the concept of inclusive fitness by Hamilton (60's, early 70's), much of altruistic behavior was seen to be readily explained and predicted by selection at the level of the individual.
Another shaping force around this time was Williams, who correctly pointed out that the notions of group selection postulated by Wynn-Edwards were simply unsupported by actual observational data, and essentially set the stage as one of the individual selection model being the most parsimonious based on observation. Moreover, he created what is still considered the generally accepted rule for examining the veracity of any group-selection model:
"Our search must be specifically directed at finding adaptations that promote group survival but are clearly neutral or detrimental to individual reproductive survival in within-group competition." (Williams, 1966)
With that in mind the onus was placed on the shoulders of group selection supporters to eliminate any possible counter explanations from an individual perspective. This criterion makes logical sense in that one must disprove all other possible scenarios before proving the existence of group selection, however one could argue that it is too restrictive, and perhaps nigh impossible to experimentally achieve.
As we started more and more to apply the idea of selection to human behavior and morphology, we again saw another debate about the possibility of group selection raised by Gould and others in the 80's. For example, Gould raised the possibility of group selection acting on race differences based on some of Wells earlier work. There is some argument as to whether Gould was strictly supporting the idea of group selection as being worthy of pursuit in and of itself, or whether he really was trying to broaden the thinking of evolutionary biologists to gain a better understanding of higher levels of interactions between organisms and their subsequent influences on selection.
Regardless, the debate has continued, for the most part from a theoretical and philosophical level, ever since. Empirical evidence to support group or multi-level selection models have typically been few and far between, and always controversial. For example, several fairly recent reviews have concluded that long-term observations of birds, mammals, and other higher organisms have not encountered populations in which group selection seems to operate. However, to counter that, other studies looking at social adaptations in microorganisms (some might remember a recent paper on slime molds that appeared on PT a few months back) have made the suggestion that group selection models do indeed best explain observations in these organisms.
Moreover, some have suggested that the observations of specific things like sex ratio bias also can only be explained with the use of multi-level selection models.
Having spent time embroiled in the middle of this controversy while a grad student at Berkeley in the late 80's/early 90's, I see the value of examining the evidence that actually supports or rejects the various models proposed by theoretical biologists and philosophers of biology. So far, I tend to think that the application of multi-level or group only models are extremely limited at best, and not of significance from the overall standpoint of looking at evolution in general.
However, as all of us are typical busy, nobody can keep on top of all the literature in an area as large as this one, so the purpose of this thread is mainly to look at the practical application of multi-level and group-level models, to see just when and where (and IF), we should be considering the application in a more general sense than we currently are.
I hope that was short enough, but not too short.
I'm going to list some general and specific references to start, and keep adding to the list as time goes on, and anybody who has read any of the papers, or has their own they wish to contribute, is encouraged to do so and argue whether or not they think the data from the articles answers the long running debate:
Is group selection necessary?
As i find online, free versions of anything, I'll add a link to it.
WYNNE-EDWARDS, V.C. 1962. Animal Dispersion in Relation to Social Behaviour. Hafner Publishing Company. New York, NY. 653 pp.
online version of RA Fisher's original models of selection (er, and everything else about the man too):
Maynard-Smith J. (1964) Nature 201: 1145−1147
a site where you can check out Gould's work (including his commentaries on group selection):
(I'll add more later)
recent reviews of empirical evidence for selection models in large organisms:
Zahavi A & Zahavi A. (1997) The Handicap Principle Oxford University Press: New York.
...and in microorganisms:
Bassler BL. (2002) Cell 109: 421−424.
some specific studies of interest old and recent:
(note this is the list that I really want to focus on, and will be adding a lot more to this a bit later)
I know there are several others over on Pharyngula that wish to add their own references, so I'll open this up to them for now, and be back to add more later, and then maybe we can pick a paper or two to dissect and discuss.
for now, I'm happy to just keep this thread open as a repository, even if there is little interest in detailed discussion.
"And the sea will grant each man new hope..."