Natural Selection in Caribou Herds - Critical Thinking Activity (6-8 Grade)

The process of natural selection requires two things – variation in a population and selective pressure. Read about the caribou and “construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals’ probability of surviving and reproducing in a specific environment.” Use simple probability statements and proportional reasoning to construct your explanations. (MS-LS4-4.)

Caribou migrate long distances over a brutally cold, snow-covered habitat every year. They eat lichens that cling to rocks and soil and grass, where available. In the winter, they must dig through ice covered snow with their hooves to reach their food. They often have to flee and/or defend themselves and their young from wolves and other predators. Males fight amongst themselves for control of groups of females, called harems, every fall during the rut for the right to breed. These conflicts use a lot of energy and sometimes result in injuries.

Herds of caribou have a variation of traits found in body and antler size, foot and hoof size, amount of hair on their feet, body posture and dominant behavior, length of legs and stride, etc. Some of these may be adaptive traits that help them survive longer and produce more young. This is called differential reproduction and can lead to these traits appearing throughout the herd over many generations. This is adaptation.

Describe, on the worksheet provided, which of the caribou’s traits might give them a selective advantage for survival in their habitat described above and for producing more young, who might carry their adaptive traits.