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Evolution

Review your understanding of evolution in this free article aligned to NGSS standards.

Key points

  • Evolution is the change in inherited traits that occurs in a group of organisms over multiple generations. Inherited traits are those that are passed from parents to offspring via genes.
    • Evolution is made possible by genetic variation, or gene differences, in a population. Genetic variation causes organisms within a population to have a range of different traits.
    • One source of genetic variation is sexual reproduction. This type of reproduction causes offspring to have different sets of alleles (and traits) compared to their parents.
    • Traits in a population can change over multiple generations of parents and offspring. New traits may arise. Or, existing traits may become more or less common. When this type of change has occurred, the group of organisms has evolved.
    • Small differences between generations can add up. With enough time, evolution can give rise to new types of organisms. For example, over many generations, one species can evolve into two.
  • Over the billions of years that life has existed on Earth, evolution has given rise to the amazing diversity of organisms on our planet.
A collage of animal images. The collage shows a frog, an owl, a tiger, a spider, a snail, a turtle, a bee on flowers, a fish, a monkey, a shark, and a butterfly.
Evolution has given rise to the amazing diversity of life on Earth. Image credit: “Animal diversity October 2007" by User:Justin, CC BY-SA 3.0.

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