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One of the most remarkable aspects of the natural world is the fit between organisms and their environments.

Coyotes, for example, have teeth and other traits that allow them to eat birds with ease. And the wings of birds, in turn, give them the chance to escape predators like coyotes.

Natural selection is the evolutionary process that generates such matches between organisms and their environments. Evolution by natural selection or adaptive evolution occurs if three conditions are met.

First, there must be variation in traits among individuals, such as the difference in color among these beetles. These trait variations stem from random genetic mutations, which occur regardless of whether they are good or bad for the organism.

Second, these trait differences must be heritable, meaning that they can be passed down from parent to offspring.

Third, some forms of the trait must provide an advantage in survival and reproduction.

Here, green beetles are better camouflaged on green grass than yellow beetles, so more yellow beetles are seen and eaten by birds.

Because of this advantage, green beetles represent a greater and greater proportion of the population over the course of generations. In this case, green color is an adaptation for beetles living in a green grassy environment.