The matter-antimatter asymmetry problem is solved by simply considering the number densities of variousspecies of non-interacting massive fermions and antifermions, the equations of which are presented andexplained in this article in the context of the evolution of the universe. Their respective number densitiesdepend on temperature and also on chemical potential of the respective species. Of great importance here isthe change in sign of the non-zero chemical potential of the respective fermion species as well as the dippingin temperature of the matter due to the expansion of the universe when comparing the equations of thenumber densities of fermions and antifermions of the respective species. This explains the initially slight andlater significant predominance of fermions over antifermions in cosmic evolution as well as the almostcomplete disappearance of antimatter in today’s universe.