Mary Midgley in The Philosophers' Magazine:
I noticed how confused current views about this are when I read a recent piece in the Guardian about how entomologists hunt the impressive Purple Emperor butterfly. Apparently they must lay out its favourite diet, which is chiefly carrion and various kinds of faeces. The writer says that Victorian observers were distressed by these tastes in such a noble animal and “observed these degraded moments with a morbid fascination. For the emperor, however, it is not a question of taste. It is thought that the males replenish themselves after mating with sodium and other chemicals from the rotting matter.”
Thus we see the conscientious butterfly holding its proboscis and resolutely taking its medicine so as to be sure of keeping its love-life in order … And this is the sort of picture that constantly emerges from contemporary evolution-talk, a picture that mixes up two quite different kinds of purpose. The butterfly’s own subjective purpose concerns what it wants to do. But the possible effect on the survival of its species is an evolutionary function, of which the butterfly knows nothing.
It is not surprising that these two ideas get mixed today. Official scientific thought doesn’t now try to distinguish between different forms of purpose; indeed it hardly recognises the concept of purpose at all. Subjective purposes – motives – were outlawed from science-speak by the behaviourists, along with the rest of our inner life. Though their effects are obviously real, they were blotted out so successfully from the perception of the learned that many conscientious thinkers still don’t dare to look at them. Instead, in a way that would have delighted B. F. Skinner, they still try to account for physical actions directly in physical terms. They pick out distinct behaviour-patterns and try to link each to an evolutionary function of its own, without reference to its meaning or its social context.
More here.