The fact that a healthy deer can outrun a timber wolf is an example of

natural selection

Explanation:

the slower, weaker deer get taken by the wolf, thus leaving the healthier faster ones that can outrun it. the healthy big strong deer has the muscle and stamina to be able to outrun the wolf. However even though the prey animals have the advantage of stamina and living in herds over most of there prey, the predator animals are smarter and are capable of stalking the prey, and in the case of a wolf pack, they are able to out smart the prey by setting up a trap to catch there prey. although wolves also have very high stamina compared to most predators, lots of times it comes down to who gets tired first.

natural selection