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Want to start a brawl at an evolution conference? Just bring up the concept of group selection: the idea that one mixed bag of individuals can be “selected” as a group over other heterogeneous groups from the same species. Biologists who would not hesitate to form a group themselves to combat creationism or intelligent design might suddenly start a pie fight to defend the principle that “it’s every man for himself.”
Yet Charles Darwin himself argued for group selection. He postulated that moral men might not do any better than immoral men but that tribes of moral men would certainly “have an immense advantage” over fractious bands of pirates. By the 1960s, however, selection at the group level was on the outs. Influential theorist George Williams acknowledged that although group selection might be possible, in real life “group-related adaptations do not, in fact, exist.”
Richard Dawkins of the University of Cambridge, whose writings have reached millions, maintains that selection might not even reach such a high level of biological organization as the individual organism. Instead, he claims, selection operates on genes—the individual is the embodiment of the selection of thousands of selfish genes, each trying to perpetuate itself.
In the past few decades, however, group selection has made a quiet comeback among evolutionary theorists. E. O. Wilson of Harvard University and David Sloan Wilson (no relation) of Binghamton University are trying to give group selection full-fledged respectability. They are rebranding it as multilevel selection theory: selection constantly takes place on multiple levels simultaneously. And how do you figure the sum of those selections in any real-world circumstance? “We simply have to examine situations on a case-by-case basis,” Sloan Wilson says.
But the Wilsons did offer some guidelines in the December 2007 issue of Quarterly Review of Biology. “Adaptation at any level,” they write, “requires a process of natural selection at the same level, and tends to be undermined by natural selection at lower levels.”
Experiments with actual groups illustrate the point. Pseudomonas fluorescens bacteria quickly suck all the dissolved oxygen out of a liquid habitat, leaving a thin habitable layer near the surface. But some bacteria spontaneously develop a beneficial mutation. These group-saving individuals secrete a polymer that enables bunches of individuals to form floating mats. As a mat, all the bacteria survive, even though most of them expend no metabolic energy producing the polymer. But if the freeloaders get greedy and reproduce too many of their kind, the mat sinks and everybody dies, altruists and freeloaders alike. Among these bacteria, then, groups that maintain enough altruists to float outcompete groups with fewer altruists than that minimum number. The former groups survive, grow and split up into daughter groups. Thus, altruistic individuals can prosper, despite the disadvantage of expending precious resources to produce the polymer.
Perhaps the biggest change that group selection brings to evolutionary theory is its implication for so-called kin selection. What looks like group selection, some theorists argue, can actually be understood as genetic relatedness. Evolutionist J.B.S. Haldane pithily explained kin selection: “I would lay down my life for two brothers or eight cousins.” In this view, altruistic bacteria in the Pseudomonas mats are saving close relatives, thereby ensuring the survival of most of the genes they themselves also carry.
Turning that argument on its head, the Wilsons assert that kin selection is a special case of group selection. “The importance of kinship,” they note, “is that it increases genetic variation among groups.” The individuals within any one group are much more like one another and much less like the individuals in any other group. And that diversity between groups presents clearer choices for group selection. Kinship thus accentuates the importance of selection at the group level as compared with individual selection within the group.
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6 Comments
Add CommentIs there really a debate about this?
Reply | Report Abuse | Link to thisWhat is the difference between individual bacteria in a group relationship, a multi-celled organism where some cell lines get advantage as the cost of others, even down to the organelles within a cell and back up to individual organisms in a symbiotic relationship that share no genes?
Every gene is "selfish". "Altruistic" genes are "selfish" in that thier behavior creates an improved condition for thier own surivial. The "struggle" that is evolution is not a all-or-nothing "game" it is merely for continued survial by any means necessary even if that means being "nice".
Studying mainstream evolution I have a hard time buying into group selection theories. When it comes down to it natural selection works on an individual level even if those changes may seen to benefit the group in the end it still benefits the individual's chances of passing genes within the group. With that said I do think it is important to continue work in this area and maybe multilevel selection theory will hold up or maybe we will realize that when all is said and done selection is working on the gene. Either way more research is needed. www.evopsych.com
Reply | Report Abuse | Link to thisConsidering your Pseudomonas fluorescens bacteria example, the relevant genes in successful non-polymer producing variants are still acting for their own individual replication. Given their new environment, containing the so called altruistic types, some have a gene which prevents them from over producing. It is this gene that will increase in frequency in future generations. There is no need to invoke any group selection, just the selection of genes which favour individual variants which are better at replicating in the new environment of polymer and non-polymer producing individuals.
Reply | Report Abuse | Link to thisBefore you incur the wrath of Dawkins, he's at Oxford, not Cambridge. And yes, it does make a difference.
Reply | Report Abuse | Link to thisInterestingly, Williams and his father, also a biologist, presented a case of group selection that was well confirmed some time before the younger Williams published his influential book. His book, Adaptation and Natural Selection, was more concerned with refuting the casual use of notions like "for the good of the species" used by the likes of Konrad Lorenz. The book was widely misinterpreted as disproving group selection in general. The reasons for this need careful historical and sociological examination.
Reply | Report Abuse | Link to thisGroup selectionists need to meet a challenge they have never been forced by their opponents to confront, at least to my knowledge, namely, to explain how they know that when they use a word like �pride� to refer to lions living together, they are actually referring to a higher-level entity rather than, for example, fifteen lions hunting, feeding, sleeping, and otherwise interacting in the same area. To put this bluntly, how do they--and how do we--know that groups exist? This question may strike almost everyone as bizarre, but the biologists do ask a similar question about species, which are groups of a sort (that is, if they exist). The reality of species has been question mostly because of their fuzzy boundaries, but someone can reasonably wonder whether, irrespective of the issue of boundaries, people who use the noun phase �the species Panthera leo� are merely referring to, say, 40,000 lions rather than a higher-level entity comprising the individual organisms. Further, imagine for a second that the species skeptics are correct and that what exist are individual lions and nothing that can be called �the lion� or �Panthera leo.� Ask yourself what exactly is lost. Evolutionary biologists can still say most of the things they want to say about the evolution of lions. The lions currently extent can still be said to be descendents of proto-lions, which in turn were descendents of proto-proto-lions, and so on. The evolutionary tree still stands, it still has roots. Now ask yourself the same question about denying the reality of smaller groups, such as packs and flocks. What is really lost by rejecting their existence and claiming that group talk--use of terms like �group�and �pack�and �flock�--is just a way of talking about individual conspecifics that are living in proximity and causally affecting each other in important ways? To help in answering this question, let me point out that the group rejectionist will redescribe the Pseudomonas fluorenscens bacteria example by saying, not that the bacteria who develop the beneficial mutation are group saving, but that their secretion of the polymer saves both their own lives and the lives of the freeloaders, at least up to the point that the freeloaders outreproduce the polymer-secreting bacteria, causing death and destruction for all. This account does not require accepting that there is some higher-level entity comprising altruists and freeloaders, it just requires acknowledging the obvious fact that what happens in the neighborhood depends on who lives in the neighborhood.
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