There is a population of green lizards and dark lizards living in the environment.
CHANGES IN GENE POOL
where is all my food ?
There is an overpopulation of green lizard and the dark lizards are struggling to survive due to predators such as hawks but the green lizards are able to blend into the green grass and produce more babies.
However due to a volcano eruption a hundred, the lava has dried resulting in the environment changing. Instead of green grass, the environment is now covered in dark black rock. Now dark lizards are able to blend in and produce while green lizards are getting eaten.
More lizards are able to reproduce than green lizards now that the dark lizards are able to survive in the environment. Now the only gene pool is dark lizards.