The theory of evolution that most modern scientists believe

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"In biology, evolution is the change in the characteristics of a species over several generations and relies on the process of natural selection. The theory of evolution is based on the idea that all species are related and gradually change over time."

Explanation:

Scientists don't believe so much in Natural selection anymore, but they do believe that evolution takes place over a very long time. The species would evolve because of a need a may have. Giraffes did not have long necks, but over time they evolved to reach the leaves. Same with some finches. Some grew sharper beaks for bigger seeds. Other stayed the same, sin ce they did not need it.

Evolution is a series of changes in an organism that takes place over many many years.

the fossil record provides evidence of a common ancestor to many species.