Because predators and prey must learn (or adapt) new ways of survival. Deer over time have learned to be much more sensitive to the surrounding environment, therefore, a deer's predator must also adapt/evolve and learn how to beat the deer at it's own game and catch it for food. Animals must evolve/adapt to any given environment. If humans lived in Antarctica for thousands of years, we would eventually be able to withstand the cold due to evolution. People who live in the Himalayas today actually breath normally at such high altitudes whereas if someone who lives at sea level went to where the Himalayan people lived, the result could potentiality be fatal because the body has not adapted/evolved at that point to withstand minimal oxygen.
