Levels of Selection

 
There's an interesting article in the latest issue of New Scientist. Bob Holmes writes about The selfless gene: Rethinking Dawkins's doctrine.

Evolutionary success is all about looking out for number one - or so most biologists would tell you. The genes that do the best job of passing themselves along to the next generation, whether by brute selfishness or canny cooperation, are the ones that flourish - a view most memorably championed by Richard Dawkins more than 30 years ago in his bestselling book The Selfish Gene.

This relentless focus on the gene may not tell the whole story, however. A small but growing coterie of evolutionary biologists argue that it leaves us blind to crucial evolutionary processes at higher scales - among groups, species and even whole ecosystem. If they are right, the popular view of evolution and the biological world needs a radical shake-up.

Almost everyone agrees that the gene's-eye view works perfectly well most of the time. "It's dominated the field, and dominated for a long time," says Michael Ruse, a philosopher of science at Florida State University in Tallahassee. Indeed, many biologists think the selfish-gene concept can explain all the intricacies thrown up by evolution, and not just the obviously selfish ones.

The article is better than most. It gives an adequate overview of group selection and species selection (sorting).

However, before reading on you should be aware of two false notions that are being perpetuated. First, there's more to evolution than adaptation and selfish genes. Not all genes are selfish and even at higher levels species sorting may occur in the absence of species selection.

Second, the concept of the selfish gene has been very important in evolutionary theory. Far more important, I think, than most people realize. But it is not correct to say that it has dominated the field, or that it's the current dogma. If you consult any evolutionary biology textbook you'll find that "selfish gene" barely gets mentioned. Almost everything is explained by considering the individual organism as the unit of selection. Dawkins has failed to convince any but a handful of evolutionary biologists that the gene perspective is a better way of looking at evolution.

The article closes with ....

It is still too early to know whether group, species and ecosystem-level selection are major evolutionary forces or merely minor curiosities - baroque ornaments on the central edifice of individual or gene-level selection. But the dominance of the "selfish gene" in evolutionary thought is facing its strongest challenge in many years.

This is a good way of putting it. Hierarchical theory is an interesting development and it is making some headway but it's fair to say that most evolutionary biologists don't think of group selection and species selection as major players.

However, the dominant thinking is that it's the individual and not the gene that forms the proper unit of selection. And the greatest challenge to the dominance of selection at the level of the either the gene or the individual is neither group selection or species selection, it's random genetic drift.

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Note: People get confused about the meaning of The Selfish Gene. Just because we talk about population genetics and changing frequencies of alleles does not mean that we are adopting Dawkins' perspective. He explains what he means by "selfish gene" in the opening chapter of The Extended Phenotype.

The thesis that I shall support is this. It is legitimate to speak of adaptations as being "for the benefit of" something, but that something is best not seen as the individual organism. It is a smaller unit which I call the active germ-line replicator. The most important kind of replicator is the "gene" or small genetic fragment. Replicators are not, of course, selected directly, but by proxy; they are judged by their phenotypic effects. Although for some purposes it is convenient to think of those phenotypic effects as being packaged together in discrete "vehicles" such as individual organisms, this is not fundamentally necessary. Rather, the replicator should be thought of as having extended phenotypic effects, consisting of all its effects on the world at large, not just its effects on the individual body in which it happens to be sitting.

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