Natural selection (1 of 4) Variation
There is variation in traits. For example, some beetles are green and some are brown.
Natural selection (3 of 4) Heredity
There is heredity. The surviving brown beetles have brown baby beetles because this trait has a genetic basis.
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.