I've changed my mind.
From what I recall of Richard Dawkins' excellent 'Climbing Mount Improbable' (Penguin, 1996), we're all mutations to a greater or lesser extent being as none of us represent exact copies of our parents. Plus we all have an awful lot of junk DNA inside us, the stuff that doesn't get used any more, dead files you might say. We evolve by means of (amongst other things) segments of DNA which switch these files off, so we're probably still carrying the stuff to grow fins (or whatever) - there's no imperative to get rid of it seeing as a piece of 'off switch' DNA performs the same function. In the unlikely event of 'off switch' DNA being lost in the copying process (unlikely I think because the numbers of er... 'safety valve' DNA thingies (you hear that? That's the sound of my analogy being stretched to the Monty Python point)) are so great that the chances of being born with something ancestral are pretty remote. Although, remote things do happen from time to time, hence throwbacks, which is what this sounds like. Mutations or rather macro-mutations (as in the development of features with no ancestral precedent) do happen although they are improbably rare, and amongst the numbers of the improbably rare it is again improbably rare that a macro-mutation will result in something that can survive for any length of time, let alone anything so useful as extra fins, eye-beams or strange magnetic powers. There's a picture in Dawkins book of a macro-mutation - a toad with eyes inside its mouth although I think he may have later disowned it as a forgery. So the dolphin sounds like a throwback.
Anyway, that's what Richard Dawkins said so any fights are better picked with him, and not me.
Observed Evolution!
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