Yet another explanation
These seem to come around regularly and rarely do they sound that convincing; this less than most, in fact.
It's obvious you can design just about anything by natural selection (c.f. the natural world) but you'd be a pretty dumb craftsman if you set out to do it that way and not use a modicum of intelligent design. For a start, you can make small sound holes, then play the violin, then make them bigger and see what changes. That's not random and I can't believe a decent craftsman wouldn't have done exactly that, many times over in fact.
Obviously, sound holes aren't the only important design factor, either, so certainly not the "secret" of Stradivari. In fact, if it were just down to dimensions, machines would be able to turn out top-quality violins by the thousand as they'd be able to accurately reproduce the dimensions of great old instruments.
And the sound holes don't just let the sound out. Among other effects, they allow the "table" (the approximate square of the top plate between the sound holes) to vibrate largely independently and affect the resonances of the whole instrument. Elongated sound holes obviously do that better.
You'd have to think the old craftsmen were really pretty stupid to have spent their whole lives breaking new ground in instrument-making and not realise just a little of this. To the extent that they were no better than a bunch of random monkeys? Pull the other one!