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Natural selection (3 of 4) Heredity

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There is heredity. The surviving brown beetles have brown baby beetles because this trait has a genetic basis.

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Natural selection (1 of 4) Variation
There is variation in traits. For example, some beetles are green and some are brown.

Natural selection (2 of 4) Differential reproduction
There is differential reproduction. Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.

Natural selection (4 of 4) End result
End result: The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown.

Natural selection in a test tube
How do biologists "evolve" RNA in a test tube? The same way that a population of organisms evolves in the real world: natural selection.

Natural selection - Beetle example
Over the course of many generations, green beetles have been selected against, and brown beetles have flourished.