Posted by: Dan | August 19, 2009

Selfish Genes

This is a re-post from a contribution of mine to Bitesize Bio.

I doubt that anyone reading Bitesize Bio has never heard of Richard Dawkins. He’s always been controversial in one way or another, ever since the release of arguably his most popular book, The Selfish Gene (Amazon US/UK). But despite Dawkins’ notoriety, maybe there are some readers here who haven’t read The Selfish Gene – I didn’t until two years ago, actually. So, what specifically is The Selfish Gene about?

Dawkins coined the term selfish gene as a way of expressing the gene-centred view of evolution, which holds that evolution is best viewed as acting on genes and that selection at the level of organisms or populations almost never overrides selection based on genes. In chapter three, he explains:

“Genes are competing directly with their alleles for survival, since their alleles in the gene pool are rivals for their slot on the chromosomes of future generations. Any gene that behaves in such a way as to increase its own survival chances in the gene pool at the expense of its alleles will, by definition, tautologously, tend to survive. The gene is the basic unit of selfishness.”

This way of looking at selection, from the perspective of the gene, gets extended to such emergent behaviors as kin selection, eusociality, and altruism, by way of the fact that an allele not only gets propogated through the gene pool by helping the immediate organism survive, it also helps other copies of itself survive in other members of its species. Meaning, altruistic behavior is a natural outcome of selection, even if it is bad for the individual organism, because the genes themselves are acting selfishly by protecting other copies of themselves. Of course most genes don’t directly influence behavior, meaning that most genes are, at best, indirectly selfish – but in the case of parochial altruism (within a family or other inbreeding group), most organisms benefiting from altruism likely carry copies of the same non-behavioral genes anyway.

At a time when the idea of group selection was being shown not to be a stable evolutionary strategy, this model provided one way of explaining why kin selection was a much better description of sociality in animals.

For these reasons, The Selfish Gene has rightfully received wide acclaim. But, it is just a metaphor, and no gene is an island. Each gene must act in concert with the rest of an organisms’ genome, which in turn must act to cooperate and compete with other members of its species and within a given ecosystem. As a result, tradeoffs get made. Many times, it is not the allele that is most effective at performing its usual task that is propogated in the gene pool, but the allele that works best with the rest of its genome to generate a successful phenotype that survives.

As a result, one of the primary scientific criticisms of The Selfish Gene has been on the idea that the gene is the unit of selection. Most even criticize the idea that the genome is the unit of selection, instead arguing that the phenotype is what is being selected. Instead, the gene is the unit of evolution, some argue, viewing evolution as the long-term trend of shifting allele frequencies.

Being a molecular biologist and not having studied evolutionary biology formally, my first reaction was to take these two perspectives at face value. After a thrashing from Larry Moran (see the comments), my conclusion that macroevolution is just a “very long-term trend of shifting allele frequencies” was blown apart. As a result, I’ve since come around to be very critical of the view that the gene is the unit of evolution.

Instead, the population appears to be the best candidate as the unit of evolution, with phyletic change (shifting allele frequencies) of a single population over time being “microevolution”, and isolation/divergence of two or more populations representing “macroevolution”.

All of this means that the impact of The Selfish Gene is very restricted as a metaphor of how evolution occurs, being successful at solving a very specific set of problems relating to social animal behavior, and is limited to discussions of phyletic change.

The implications for social behavior coming out of The Selfish Gene has also directed much of Richard Dawkins’ career since its publication. His follow-up book, The Extended Phenotype, subtitled “The Gene as the Unit of Selection”, and later, “The Long Reach of the Gene”, argued that a gene may effect an organism’s environment through that organism’s behaviour, citing as examples caddis houses and beaver dams.

He also coined the term “meme” (the cultural equivalent of a gene) to describe how Darwinian principles might be extended to explain the spread of ideas and cultural phenomena, an idea that has been developed into a new area of study principally by Susan Blackmore. Dawkins used the word meme to refer to any cultural entity which an observer might consider a replicator. He hypothesised that people could view many cultural entities as capable of such replication, generally through exposure to humans, who have evolved as efficient (although not perfect) copiers of information and behaviour. Most notably in his more recent book, The God Delusion, he argues that religions are basically memes (among other things).

I don’t know if his arguments about religions as memes are all that great, but he sparks discussion either way about how it is useful to view the origins of social behaviors. But that’s a story for another post, some other time.



%d bloggers like this: