It simply isn't true, for example, that being big is in general better for fitness than being small except when there are effects of interacting variables; or that flying slow and high is in general better for fitness than flying fast and low except when there are effects of interacting variables; or that being monogamous is in general better for fitness than being polygamous... except when there are effects of interacting variables... It's not that the underlying generalizations are there but imperceptible in the ambient noise.
Jerry FodorFaculty Psychology is getting to be respectable again after centuries of hanging around with phrenologists and other dubious types. By faculty psychology I mean, roughly, the view that many fundamentally different kinds of psychological mechanisms must be postulated in order to explain the facts of mental life. Faculty psychology takes seriously the apparent heterogeneity of the mental and is impressed by such prima facie differences as between, say, sensation and perception, volition and cognition, learning and remembering, or language and thought.
Jerry Fodor...monetary exchanges have interesting things in common; Gresham's law, if true, says what one of these interesting things is. But what is interesting about monetary exchanges is surely not their commonalities under physical description. A natural kind like a monetary exchange could turn out to be co-extensive with a physical natural kind; but if it did, that would be an accident on a cosmic scale.
Jerry Fodor