Answer :
If by "beneficial" you mean "more suited to its environment," then the answer would be natural selection. Natural selection is the process by which, over time, the individuals of a species that have the traits most suited to their environment survive at the highest rate, leading to an increase in the proportion of individuals that possess those "beneficial" traits.
A note here: natural selection is not something that is "used." Rather, it is a process that occurs naturally. This is why they say the environment "selects" for certain traits in a species. This same process can be harnessed by humans to breed a larger population of animals that possess a certain valuable trait that only a few members possess at the current point in time, but this process is called "artificial selection."
