Traits that improve an animal's chances of survival are adaptations. Adaptations can be a physical change to an organism or a behavioral change that affects the way an organism acts.
Adaptations start off as genetic or mutational changes in an animal's DNA. If the change is favorable, it is passed down through the organism's offspring. As more and more individuals in a species inherit the mutation, it becomes a normal part of the species, thus an adaptation. An example of a physical adaptation is the way certain plants have evolved to store water in their leaves and stems when growing in the desert. Animal migration is an example of a behavioral adaptation, as seen in gray whales that migrate from colder waters to warmer waters in order to give birth.
Adaptations usually develop as a result of changes that happen in an organism's environment. A notable example is the English spotted moth. Prior to the industrial revolution, the most common type of moth coloration was cream colored with few spots. However, a few showed mutations that changed their color to gray or black. As the industrial revolution continued, the cream colored moths died out, and the gray and black ones thrived. This is because they better blended in with the trees covered in pollution, meaning predators were more likely to prey upon cream-colored moths than the darker ones, which left the darker moths to reproduce and pass on the mutation to their offspring.