Years ago, my wife worked with yeast in a genetics lab. For some reason which I can no longer recall, she needed to "create" yeast that could digest a sugar called galactose. The yeast she was starting with naturally digest a different sugar (glucose). So how do do this? You take a bunch of naturally occuring yeast and hit it with a low level of radiation to induce mutations. Then you stick them in a petri dish with nothing but galactose. Voila, a few day later you have a petri dish full of galactose-eating yeast. There was nothing random about this outcome. Yes, the radiation induces random mutations and, by chance, some of the mutations lead to yeast cells capable of digesting galactose. But it is the selection pressure induced by the environment that ensures that only those mutants survive and the rest die off.