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Different plants and animals have features that help them live in different places.

Some kinds of organisms that onced lived on Earth have completely disappeared.

All species are different.

All organisms have similar needs and structures.

Some organisms that lived long ago are similar to organisms that live today while others are different.

Some individual differences provide better opportunities for surviving and reproducing.

Extinction means there are no living organisms of a certain species..

Millions of species of animals, plants, and microorganisms are alive today. Although different species might look different, the internal structures among organisms is similar, their chemical processes, and common ancestry.

Biological evolution explains how the diversity of life and the uniqueness of each species' properties developed through a slow processes over many generations through biological adaptation, which involves the selection of naturally occurring variations in populations, which include changes in structures, behaviors, or physiology that enhance survival and reproduction success in a particular environment. Small differences can accumulate in successive generations so that descendants are very different from their ancestors. Individual organisms with certain traits are more likely to survive and reproduce. Changes in environment can affect the survival of individuals and entire species.

Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to allow its survival. Fossils indicate that many organisms that lived long ago are extinct. Extinction of species is common; most of the species that have lived on the earth no longer exist.