A moment on my evolution education soapbox: Evolution doesn't "give" you things. A species evolves and mutations either carry through in their offspring, or not. Evolution does not have a bag of goodies in store. Evolution is not a thing, person, activity, whatever. It's a description of a broadly random process, that viewed from the outside, looking back, seems to make some kind of sensible order.
When the barbed willies came along, and ever since, there have probably been all sorts of small variations in guppies that never made it along the chain.