Darwin's theory of natural selection was based on the idea that traits are often _______.

More offspring are produced than can _______ in their environment.

The source of new heritable traits in a population is _______ mutations.

Over generations, populations become _______ to their environment.

Traits that are _______ in one environment might be harmful in another.

Natural selection acts on _______ variation in a population.

Groups that can no longer interbreed due to geographical barriers may become separate _______.

Sexual reproduction creates variation by mixing and matching _______ variants.

heritable, survive, random, adapted, helpful, separate species, gene