In presenting a group selectionist account of sociobiology, Wilson and Wilson argue that alternatives such as kin selection are not really alternatives.
Kin selection and multiplayer games
Attacking the third leg of the tripod, W&W argue that even genic or individual selectionist accounts implicit include the existence of groups as a factor in evolution. This resolves, as far as I can see, to the view that equivalence classes in genetic selection form a group: if a population is composed of alleles A and a, the individuals with one of these alleles socially interact with their conallelics, as well as with the other group.
Second, interactions between trait groups are implicitly group selectionist even if the traits are seen as borne by individuals, and population is structured accordingly. Third, these equivalence classes evolve via interactions between trait groups - that is, there needs to be between-group selection for the population to evolve. I don't quite know what to make of this argument. If I read it aright, it seems vapid. Gene selection accounts of course involve interactions between N individuals, but the mere fact they are equivalence classes doesn't make them selective players as groups.
They claim, possibly with justification given their redescription of the notion of a group, that Hamiltonian inclusive fitness is a kind of group selection, and that Hamilton himself accepted this. But is their definition of a group anything new? That individuals interact in a population, and that fitness is determined by one's neighbours in part, is nothing much new. It's called density dependent selection. For those who don't know it, it works like this:
Suppose you have the eponymous altruists and cheaters in a small population. If altruists outnumber cheaters to a certain ratio (which depends on the payoff matrix) then the occasional cheater will not lower the altruists' payoffs (fitness) noticeably, but the cheater does very well indeed. But in a population of mostly cheaters, the altruist does very badly while the cheaters do less well than in the other population. Now make these populations subpopulations of a larger one... W&W say:
All of these models obey the following simple rule, regardless of the value of N, the duration of the groups, or other aspects of population structure: Selﬁshness beats altruism within single groups. Altruistic groups beat selﬁsh groups. The main exception to this rule involves models that result in multiple local equilibria, which are internally stable by definition. In this case, group selection can favor the local equilibria that function best at the group level, a phenomenon sometimes called “equilibrium selection”...
Is this group selection? I think that the answer depends solely on one's terminology, and not on any theoretical difference between individual selectionists and group selectionists. Population geneticists using "standard" models accommodate this just fine. It seems to me that the debate has moved from being substantively theoretical to being a matter of words. W&W seem to agree. They say "They [the different models] differ, however, in how they partition selection into component vectors along the way. The frameworks are largely intertranslatable and broadly overlap in the kinds of traits and population structures that they consider." So the next move of W&W strikes me as somewhat unnecessary.
They argue next that the "selfish gene" approach of Williams and Dawkins rejected selection above the individual. I think this is false - Williams himself in 1966 identified a case of group selection of the segregation distorter t-allele in mice, based on a study done by Lewontin and others. But thinking this, they assert
When Williams and others rejected group selection, they were rejecting the possibility that adaptations evolve above the level of individual organisms. This is not a matter of perspective, but a fundamental biological claim. If true, it is every bit as momentous as it appeared to be in the 1960s. If false, then its retraction is equally momentous.
So they discuss three examples of "pluralism", or attempts to give multiple levels of selection. The first is Hamilton's inclusive fitness model of kin selection, the second is Kerr and Godfrey Smith's (two philosophers) distinction between collective and contextual fitness. The third is the failure of the Price equation to properly classify fitness bearers. I will leave you to read this discussion for yourself.
The point of this, however, is that W&W claim that we need a core set of criteria that applies to all cases of putative selection. In effect, they reject pluralist perspectives in favour of a monism, which can be summarised thus:
1. A distinction between group and individual fitness. In short, they deny that these are intertranslateable.
2. Locally or individually disadvantageous traits can only evolve through group selection.
3. There is no general reason to think group selection is a weak or inactive force in evolution. So we must evaluate each case on its own merits.
4. Traits that evolve throughout a population may yet be the outcome of group selection. They say
If we are merely interested in whether a given trait evolves, then it is not necessary to examine levels of selection, and multiple perspectives can be useful. If we want to address the particular biological issues associated with multilevel selection, then we are required to examine the appropriate information and the perspectives converge with each other.
They then appeal to Maynard Smith and Szathmáry's "transitions" concept, which is the next post. Then I will (finally) give my own thoughts on this whole matter.
Two things occur to me.
Firstly, pinning down exactly what level selection works at is a lot harder that most people make out, IMHO. In particular, in populations of sexually-reproducing but non-selfing organisms, an individual on its own has no fitness. Not a sausage. So working logically out from that, even the most "selfish" gene is working in a population gene pool, albeit expressed via an individual that may act to maximise its individual fitness. If that makes sense. I'm of the opinion that the selfish gene paradigm is easily abused and not that useful, but anyway...
Thing the second: it's increasingly being shown that animals in groups actively punish "cheats", often with dire consequences for the cheat. Everything from fish inspecting predators in pairs to vampire bats feeding each other; animals remember these interactions, and pretty soon no-one will deal with a cheat. In vampire bat society, cheats die.
Loving these posts, John, thanks.
Good point, Chris. I hadn't thought of the individual having a fitness on its own. Even worse, I think that an asexual organism has no fitness on its own: it has no benchmark fitness to be better or worse than. It has a rate of reproduction depending on circumstances and conditions, ranging from negative to non-Malthusian hyperbolic growth, but it has no fitness unless there is some variance in heredity.
I'm not sure about that. Anyone?
Actually, I would have said things were a lot simpler with an asexual species: the same set of genes goes from parent to offspring down the whole lineage, rather than being mixed up and recombined.
Now, as for defining "species" in asexual organisms... you can argue (for several different definitions) that each lineage is a species!
You can, but you shouldn't. See my Microbial species posts (in the Best of ET tab), or email me for a copy of my paper on the topic.
I'm in the fortunate position of not having to think too much about species concepts, and I'm very happy to keep it that way ;)
2. Locally or individually disadvantageous traits can only evolve through group selection.
Are they re-defining kin selection as group selection, and declaring victory? That's a bit naughty, given the history of the debate. It's also at least
8 years behind the times (enjoy - there are a couple of stonking lines in there!).
In particular, in populations of sexually-reproducing but non-selfing organisms, an individual on its own has no fitness.
True, but put it in an environment with others of its species, and it can reproduce and hence have fitness. But fitness is always defined as being specific to an environment, and that can include conspecifics.
It has a rate of reproduction depending on circumstances and conditions, ranging from negative to non-Malthusian hyperbolic growth, ...
But that's the definition of (absolute) fitness! It's Fisher's starting point for his Genetical Theory. Relative fitness is then the relative growth rates, and all the maths works out in the end (well, except in the US where they only have one math).
Very interesting series of posts! Thank you for bringing this article to my attention! Despite not beeing an evolutionary theoretist myself I thought I had the whole altruism thing figured out (reasoning entirely from a kin selection/inclusive fitness theory perspective) and was under the impression that group selection had been entirely dismissed of during the sixties. But apparently there are different perspectives out there!
Reading the two Wilsons article forced me to reevaluate some of the foundations of my beliefs about the evolutionary forces of sociobiology - however, I'm still not very convinced about many of their arguments. Especially not after reading the article by West et al. that was referred to in one of the comments to your previous post. It would seem that much of the controversy of what they are saying boils down to just a question of semantics. The Wilsons obviously prefer to describe some of the evolutionary forces in terms of group selection (or multilevel selection theory) others prefer to describe them using the inclusive fitness theory - basically it would seem to be just the same thing...
I am considerably more confused now than when I started reading - and that must be a good thing!