Whatever the silliness and arrogance of his views on religion, the Dawkins of _The Extended Phenotype_ continues to fascinate me. The idea that genes are selected as much for their effects on other phenotypes as on those of the bodies that carry them is one of these simple, blinding illuminations that make you wonder how anyone could not have seen it before.
Most of his examples are about parasites of lower animals — my favourite a fluke which makes ants climb to the top of blades of grass, where they are more likely to be eaten by sheep, which are required for the next stage of the fluke’s lifestyle.
But you can perfectly well understand the plants addictive to humans in the same way. Or, indeed, brewer’s yeast. The genes that cause cannabis to generate THC or tobacco to generate nicotine, also act on human brain phenotypes in ways which cause humans to behave in certain ways — ie to plant them, nurture them, breed them selectively, etc, which increase the population of such genes in the world. Whether you regard this as parasitism or symbiosis is a nice point, but I think on balance it is parasitism.
So I think this is a clear example of the way in which Dawkins is quite simply right to see that genes have an existence independent of the bodies they find themselves in. At the same time, it is a deficient example of causation. It’s true that certain genes in certain plants make humans behave in certain ways. But we all know huge differences in individual tolerance and reactions. Nor do drug chemicals make whole societies behave like that. Some societies invent vineyards, some, prohibition. So, while it is clearly true that tobacco grows in Macedonia today and cannabis in wardrobes in Enfield, because of the effect that the products of some of their genes have on human brains, this is only an additive cause, one necessary rather than sufficient.
On the other hand, thinking of drugs as parasitic on humans — and from this it is a short step to the idea of their being spiritual or metaphysical entities, like “memes” — might be helpful as a way of turning people against their use, and thus in its own way effective. Like “Demon rum”, in fact.
fn1. this is from memory, and if I write the thought up for CiF I will check the details. Ant, grass, sheep are all correct. But I can’t remember which parasite.