Harbor seals live in northern oceans and have a layer of blubber (fat) that keeps them warm. Seals can have blubber of different thicknesses. Seals with thicker blubber are more likely to stay warm and survive in cold ocean waters. But, in warm ocean waters, thicker blubber can make the seals overheat and die.

(First picture)

Harbor seals live in northern oceans and have a layer of blubber (fat) that keeps them warm. Seals can have blubber of different thicknesses.

Seals with thicker blubber are more likely to stay warm and survive in cold ocean waters. But, in warm ocean waters, thicker blubber can make the seals overheat and die.

Diagram titled Population Before containing 2 rows of seal icons. The first row is labeled Medium Blubber and contains 2 seal icons. The second row is labeled Thin Blubber and contains 9 seal icons.

The diagram above shows a population of seals that lived in an area of ocean. Scientists had previously only seen seals with medium or thin blubber in this area of ocean; they had never seen seals with thick blubber.

The diagram below shows how the population changed after many generations.

(second picture)

Edin says the change in the seal population was caused by a change in the environment.

Vada says the change was caused by a mutation.

Miko thinks both Edin and Vada are correct.

Who do you think is right? Explain what happened to the seals over many generations.