The notion that the traits that help a species survive and reproduce are passed along more frequently than those that do not (i. e. differential reproduction and adaptation) is known as

Natural selection

Explanation:

According to  Darwin's theory, natural selection is the process by which individuals better adapted to their environments have more chances to survive and reproduce, and thereby their descendants will be better represented in the next generation. This mechanism exploits the existence of natural variation among members in the population which is used to select those individuals that are better adapted (i.e., with a higher adaptive fitness) for their environments. Natural selection is a key mechanism of evolution by which species change across time.

one comes through sex and the other does not lul im not

then that particular organisms become extinct.