Animals gradually adapt to changes within their environment over time. This gives them a better chance of surviving rather than going extinct because of the change. Say there is a gene mutation affecting color within a population of beetles in a rain-forest. All of the beetles used to be red, but now a few of them have experienced a gene mutation and are green. Because they live in a rain-forest, it is likely that the green beetles would blend in with their surroundings far better than the original red beetles, and those red beetles would be wiped out by predators because they are easier to spot. The green beetles would live on and flourish, and their population would increase. Soon there would be few or none red beetles, and many green beetles.
