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It’s a beautiful example, which I wish had been available when I wrote The Extended Phenotype. The altered rat behaviour is an adaptation for the benefit of T.gondii genes, specifically those T.gondii genes that express themselves in the rat brains that they inhabit.

I repeat, it is especially pleasing that this effect is achieved, not in a boring way simply by making the rats sick and therefore more sluggish in escaping from cats. Indeed, they seem to have no obvious effect on the general health of rats. Their effect is a specific manipulation of rat behaviour vis-a-vis cats. It’s as though they are pulling puppet strings in the rat’s brain. A neurophysiologist would not be surprised to discover a way of doing exactly that, either with micro-electrodes in rat brain cells or with drugs. Or geneticists could do it by genetic manipulation of rat genes. It seems that natural selection, working on protozoan genes, has achieved exactly the same thing.