Which mechanism are responsible for introducing new allies into a population’s gene pool a gene flow b emigration c niche shift d natural selection

Well...to answer and explain this answer to,you got to think on the simple possibilities. Let's look at the answer natural selection. As you may know,natural selection is the survival of the strongest(or fittest). Nature is picking the best of alleles for the gene pool. Ex. Humans who can survive the harshest of weather or diseases will be chosen to reproduce and keep the genes going.

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I believe it’s A but I’m not exactly sure