A stimulus is anything that causes an organism to react. Examples of stimuli include heat, light, gravity, or sound. Generally speaking, organisms will react to a stimulus in a way that will increase its chances for survival. Homeostasis is defined as a process by which an organism responds in order to preserve the conditions necessary for life. If we get too hot or too cold, our bodies respond by sweating or shivering.
Most organisms can produce more offspring than are able to survive.
The genes responsible for the survival of most organisms is reproduced more often producing changes in the organism and also eventually in the environment. This process is known as natural selection . This moth was mostly light-colored. The light-colored moth could land on trees and not be seen by its predators. However, as the industrial revolution progressed, the tree trunks began to darken due to the pollution in the country.