Just throwing this out there:Evolution of arthropod silks
dorsk188:
Oh, I thought of another possible mammalian analogue to silk. Males do forcefully expel fluids that coagulate rapidly when exposed to air. Again, I can’t imagine it being used as silk is, but I never underestimate the font of human ingenuity.
Way to drag a perfectly family-friendly discussion right into the gutter.
Oh, break out of the Victorian culture prison already. This is a discussion about biology, and my point was both relevant and restrained.
(Incidentally, how is sperm not family-friendly? It’s one of the chief ingredients!)
Frylock
January 29, 2012, 4:18am
24
Smeghead:
Evolution is, at its heart, driven by a random process - mutation. Thus, nearly always, the only real answer to the question “Why did evolution not do…” is “because it didn’t”. We can speculate, as you see here, about how something that seems useful may not be as useful as we think, or how the same function is done by something else, but as has been said, just because something’s useful doesn’t mean it’s going to pop up by a random mutation.
We could wax philosophical here about fitness landscapes and local versus global maxima, but that’s really just saying the same thing.
The OP opened with a remark that, according to his reading, spider silk evolved several times independently. If it’s true that silk spinning evolved several times independently within a single branch of the evolutionary tree, then there is something to ask–what is it about that branch that predisposes it to have members that evolve silk spinning mechanisms?