Answer:

Hardy-Weinberg (& Castle) Theorem - 1908, G. H. Hardy and W. Weinberg and W. Castle independently disproved the naive supposition that by numerical prevalence, an allele will become more common through time (i.e., gene frequencies change on their own, randomly)

In the absence of evolutionary processes, gene frequencies will stay the same through time.

Several assumptions are made: No mutation, No migration, No selection, No inbreeding (i.e., an infinitely large population), No drift (i.e. same as above), Completely random mating

Three points made by the H-W theorem:

Allele frequencies do not change from one generation to the next
equilibrium genotype frequencies do not change and are given by the H-W formula
Equilibrium is attained in a single generation (if the allele frequencies are the same in both sexes)