The small species of seal, live in the artic that's surrounded in white snow. The seals are eaten by a hungry polar bear that lurks around the artic waters.
More seals are being birthed then the waterline can hold. There's not enough food and space for the seal can be held. Some of the seals are eaten by the polar bear.
Not all the seals are born white. Some of them can be of different colors. All the seals are competing to stay hidden and alive from the polar bear so they can live and not be the next meal of a polar bear. "GET SNATCHED"
The colored seals stand out in the white area, making them easy to be hunted by the polar bear. and the white seals are easier to hide from the polar bear.
Because of the color of the snow, the white seals are able to avoid the polar bear better. White seals are eaten less often and are easier to survive longer.
Only the surviving seals get a chance to reproduce. Because most of the seals are white, they pass on their white color trait to there offspring. Therefore, a greater percentage of seals are white in the next generation.