For this natural selection story, focus on just ONE GENETIC TRAIT that has two alleles. This is a make-believe story but the story line should sound plausible. Do not involve humans in any way. Once...

For this natural selection story, focus on just ONE GENETIC TRAIT that has two alleles. This is a make-believe story but the story line should sound plausible. Do not involve humans in any way. Once upon a time there was a population of polar bears. Most of the polar bears had/were_(a)___ but a small proportion of the population had/were__(b) ___ Over many generations, the proportion of bears expressing the rare allele became more common through natural selection. What was going on within this population to cause this shift? ___(c)_(very brief is great!) Note: do NOT mention whether the alleles are dominant/recessive nor about individuals being homozygous etc. We are looking at the big picture population-level patterns only.