Australians have a problem with rabbits.
They built a fence to stop the spread. Bunnies die of hunger, as they are unable to cross it.
Now, an evolutionary dilemma:

How to evolve?
A small mutation could make a male rabbit jump higher and up the fence.
Another could make a female rabbit grow teeth to cut barbwires.*
But, in all likelihood, the offspring of this putative rabbit couple will lose the mutations. Pure statistics.

Conclusion:
Imposing fitness doesn't alone create function.

So: adaptation doesn't work under pressure.**

How is that for counter intuitive.

*Even with the assumption that the step of evolution in these two cases is possible.
** More (and better) on this: 'Spandrels of San Marcos', by Stephan J. Gould and Richard Lewontin (1978).