Levels of selection
In the period in which sociobiology was first proposed under that label (from now on, the term sociobiology refers to this period, as outlined in Ullica Segerstråle's Defenders of the Truth: The Battle for Science in the Sociobiology Debate and Beyond), there was an ongoing debate over whether gene-level selection was the sole form of selection, or whether some kind of group selection was also in play. W&W argue that, given the developments of what has come to be called multi-level selection theory, the time has come for a re-evaluation of sociobiology.
They spend some time discussing this history, and, as I would, say that they will use terms like group selection and sociobiology at their face value. This matters because connotations often lead critics to employ history to attack current arguments. For that reason, I will replace the term sociobiology with social biology, an older and more general term. The project here is to understand human social behaviour in biological terms, not to defend Ed Wilson's Sociobiology: The New Synthesis. So when I say I have become an unrepentant sociobiologist, I really intend to mean I take social biology to be a legitimate and fruitful research program.
I won't go into the detail of their historical review. Suffice it to say that the debate set forth by George Williams' attack on V. C. Wynne Edwards' group selection is the backdrop to attacks on social biology. But as Williams himself noted, group selection explanations were not prohibited, just a hypothesis to have recourse to only when individual level (i.e., organismic) selectionist explanations had failed. This is often overlooked by individual selectionists. They say:
The rejection of group selection in the 1960s was based on three arguments, like the legs of a stool: a) group selection as a signiﬁcant evolutionary force is theoretically implausible; b) there is no solid empirical evidence for group selection as a distinctive, analytically separable process; and c) alternative theories can explain the evolution of apparent altruism without invoking group selection. In the following sections, we will show that all three arguments have failed, based on subsequent research. If this information had been available to Williams and others in the 1960s, the history of sociobiology would have headed in a completely different direction.
The debate over (behavioural) altruism has shifted a lot since then, to be sure, and one of the key works that made this happen is David Sloan Wilson's own book, in collaboration with the philosopher Elliot Sober, Unto Others: The Evolution and Psychology of Unselfish Behavior. This work relies upon a limited form of group selection not dissimilar to Darwin's own form in The Descent of Man. It is basically kin selection qua Hamilton applied to temporary segregation into groups, what they term the Haystack Model after Lewontin's example case. Mice that assort into haystacks to breed will have some ratio of altruists to defectors, and the haystacks that have the higher number of altruists will be more fecund, so that the overall ratio in the general population will rise in favour of altruists. This is, it need not be said, a quite different kind of group selection; the old kind is sometimes called naive group selection, in which the benefit to the group drives evolution, but the new kind, the multi-level selection theory, is arguably equivalent to different kinds of lower level selection under density dependence. That is, you can translate it from one level to another, without requiring that any single level (i.e., the gene) is privileged as "the" level of selection.
Sloan Wilson has long argued that the variance at the genetic level doesn't automatically covary with the phenotypic effects, and that for some purposes, it is better to think of selection occurring at the phenotypic level rather than the genetic. For example, the "quorum sensing" aspects of between-organism signalling leads to larger scale effects with little genetic variance. So it makes sense to talk about selection at that level rather than the genetic. This is a kind of "group" selection, but not one that commits the errors Williams identified in 1966. Instead, it proposes that a level of selection is the trait group or a collection of organisms within a population that share, as a whole, a particular trait.
The argument that group selection is theoretically implausible is basically the claim that the effects of group selection, or selection at a level higher than the genetic or individual, cannot counterbalance the "selfish gene" selection, because it is too weak. Groups of the Haystack kind persist for less than a single generation, and so selection for them must be much less efficacious than selection for "eternal" genes (or rather, alleles). This is roundly denied by Sloan Wilson and those who propose trait group selection. I should add here that they do not expect trait group selection will always trump individual selection, but only that under special conditions (which may or may not be common) it can.
I will not review their empirical section in favour of group selection, as most of the facts are agreed by all, and only the interpretation is at issue. For some time now, the debate has been over whether group selection and individual or allele selection is equivalent, or whether, as Okasha has argued, genic selectionism commits an "averaging fallacy" and if so, whether that supports a group level account instead.
In any case, W&W hold that group selection, of the trait group kind, is valid, and can support sociobiology.
In the next post, I will consider their arguments about kin selection and pluralism.
Do W&W call their group selection "trait group selection"? I think Sloan W. caused a lot of unnecessary friction by not distancing his form of groups selection (which has mathematical models, so is therefore Officially OK) from the old Wynne-Edwards variety.
There's a really good theoretical evolutionary biologist called Laurent Lehmann who argues that kin and group selection are the same thing, because you use the Price equation approach to model both. He even makes the point that you can use it to model evolution on two different planets.
Yeah, I agree with Bob O'H. Kin selection can be construed as a form of group selection. The full covariance derivation of kin selection, revealing its multilevel properties, is found in Chapter 10 of Sean H Rice's book "Evolutionary Theory," along with a discussion of the multi-level selection in general.
There's a really good theoretical evolutionary biologist called Laurent Lehmann who argues that kin and group selection are the same thing...
And others as well:
It has since been shown that kin selection and new group selection are just different ways of conceptualizing the same evolutionary process. They are mathematically identical, and hence are both valid...
Inclusive fitness is a generalization of Darwinian fitness, and inclusive fitness theory (kin selection in its broadest form) is a generalized description of natural selection, and these are not simply special cases that are appropriate only for when individuals interact with their relatives.
The new group selection models do not rely on the maintenance of whole groups, and so the terms trait-group or demic selection are perhaps more appropriate. An alternative is to state as simply as possible what they are - models of nonrandom assortment of altruistic genes (e.g. because of relatedness, or altruists choosing to interact with each other; Maynard Smith, 1976). When this is done, the links with inclusive fitness theory become transparently clear. The potential meanings for 'group selection' are so numerous because the partitioning of selection into within-group and between-group components can be done for any arbitrarily defined group (Wade, 1985). Indeed, group selection has also been used to describe species level sorting (Williams, 1992), and new variants are being introduced such as 'cultural group selection' (see below). These points emphasize the use and power of Hamilton's original terminology, and the gains to be made from the minimal use of jargon.
In light of this, I find the elder Wilson's abandonment of kin selection a bit puzzling, as apparently do others.