The Essence of Ecology

extinction - a species is extinct when it no longer exists on Earth. Sometimes extinction is caused by huge natural disasters, like the ice age. Sometimes humans have hunted animals until there are no more left, like the Dodo bird or the passenger pigeon.
evolution - evolution is the process of change over time that can be seen in a species. Evidence from fossils shows us that human beings have changed gradually over millions of years to become the way we are today. The first fossils show that humans did not make tools and did not speak. Later fossils show that both tool-making and language developed. Organisms usually only change when that change is a benefit to them over time.