They are not claiming that the radiation led to evolution of an entirely new gene..that would be unprecedented. You don't get "brand new genes" in that kind of

They are not claiming that the radiation led to evolution of an entirely new gene..that would be unprecedented. You don't get "brand new genes" in that kind of evolutionary time frame. Also, there is not single gene for melanin. Several genes are required for the ultimate effect that you observe as dark skin. A mutation in any of these genes, or in any of the transcription factors which control expression of these genes, could lead to observed differences in frog skin color. FYI, "new genes" are usually the result of duplication of an existing gene (https://en.wikipedia.org/wiki/Gene_duplication#Mechanisms_of_duplication https://en.wikipedia.org/wiki/Gene_duplication#Mechanisms_of...). Duplicating a gene can be useful in and of itself by providing functional redundancy. However, the new copy is then also subject to its own mutations without affecting the original copy, and over time the two genes may diverge in function.