Hello there.
Why did identifying rock layers because of their fossils become important?
It was the first indication that the layers were from different ages.
They are held together by weak hydrogen bonds
Frogs lay eggs under water. When they hatch they are called tadpoles. After a time as tadpoles they undergo metamorphosis where they grow legs and lungs and become the little friendly hippidy hoppidy guys you see on your porch every night.
Natural Selection proposes that organisms that are better adapted to their environment are able to survive and reproduce.
Even though these frogs are the same species, their shades of green is what helps them to survive in their habitat. In this case, frogs with a lighter shade of green are able to be seen by predators easier, whereas frogs with darker shades are able to blend in (camouflage) more with their surroundings. After a period of time, due to them being easily seen, lighter-shaded green frogs will die off.
To anseer your question, natural selection would have a gradual affect on the frequency of the alleles. Lighter-green allele frequencies would eventually cut off, and darker-green allele frequencies will increase.
Hopefully the following image will help:
As seen in the image, (please forgive the quality, as I had drawn this on some random kids drawing site on the internet...) you can see the affects of natural selection on the allele frequencies. The brighter-green shades gradually decrease over time, as the darker shades increase.
Hope you find this helpful.
Most color pigmentation goes towards hair and not much is left for skin.