Yes. The pure luck that their ancestors just happened a tiny bit more like a leaf than their fellows, due to a random mutation or random environmental factor a

Yes. The pure luck that their ancestors just happened a tiny bit more like a leaf than their fellows, due to a random mutation or random environmental factor affecting gene expression. Over time, many tiny bits of pure luck accreted as something that actually looked almost exactly like a leaf. Natural selection is 100% pure luck. Sexual selection may be as well.