Populations of organisms evolve by natural selection.

*Individual organisms with certain traits are more likely than others to survive and have offspring.
*Every organism has a set of instructions for specifying its traits.
*Hereditary information (set of instructions) is contained in genes, located on chromosomes.
*Each gene carries a single unit of information.
*A human cell contains many different genes.
*Organisms reproduce and pass their genes to the next generation (their offspring).
*Genes can randomly change or mutate, causing changes in certain traits of the offspring.
*Changes in environmental conditions can affect the survival of populations and entire species.
*Small differences in organisms can accumulate in successive generations so that descendents are very different from their ancestors.
*Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to allow its survival.

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