By chance?

[Mister Agenda]

Well what I’m saying is that mutations ARE like magic. As Luck and magic would have it , look what they accomplished, among everything from owls, eyes. to blood clotting to the insect doppelgänger of a leaf and many other examples of traits that seem too good to be true.
And.  What did your parents say about things that are usually too good to be true?
If I was stuck in the middle of the desert dying of thirst what would the chances be that a case of spring water would be behind the next rock?

Evolution is not too good to be true. 99% of all the species that ever existed are extinct, essentially because they did not find that spring behind the next rock when their reproductive fitness environment changed.

If there were 100 million people in that desert, do you see how it's a whole different game to bet that ONE of them will find spring water behind the next rock? And that that is the one that will survive?

If a million butterflies have regular spots and one butterfly has slightly larger spots that give it a better chance of surviving to reproduce, that's great for that butterfly, but the rest are doomed (in the particular case of the Owl Butterfly species) to have their 'small spot genes' gradually out-competed by and replaced by that one lucky butterfly's 'slightly larger spot genes'.