Decent answer :)

The only thing I'd add (and I'm simplifying a lot here) is that if you imagine that the cells in the body are constantly signalling to each other, at various tipping points, one (or more) signal becomes more dominant than the other which in turn can trigger new behaviours.

So, the absolute trigger isn't often evident as it is the result of systemic change in cell function.

And executives of companies. They always seem to suffer from Windowitis.

Would be helpful if we had meaningful therapies.

But think of the fun you've had. You can't put a price on that.

Probably, but like many things it seems very hard to identify the actual trigger proteins / enzymes or whatever. It's fascinating to study but depressing how little we know.

Incidentally, I think the initial cell fusion that kicks off the growth process is equally interesting. We know some but not all of the protein interactions.

Great question, I've been asking it for years. The answer remains unknown.