This is a species of harp seals that have been reproducing together for millions of years. There is high gene flow between the members of this species.
As the earth falls into a heat age that lasts for several hundred years, the ice where the seals live begins to melt and the climate becomes warmer.
Due to the melting ice, the seals are separated into two groups forced to move inland towards the remaining ice in different locations and the gene flow within the species decreases because the two groups can no longer mate together.
Over thousands of years, the climate reverts back from a heat age to an ice age, once again cooling the earth.
The ice age causes the ice and glaciers to freeze, allowing the two groups of harp seals to reunite in their old home, but do to random genetic mutations and natural sele