2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/41986Operating with the bilarge neutrino mixing, we show that in the option of Dirac neutrinos the fermion universality -- expressed by the proportionality of neutrino masses to charged-lepton masses -- predicts $Δm_{21}^2$ of the order $10^{-5} {\rm eV}^2$, consistently with the LMA MSW solar solution. In contrast, in the option of Majorana neutrinos the fermion universality -- introduced as the seesaw proportionality of neutrino masses to charged-lepton masses squared -- predicts $Δm_{21}^2$ of the order $10^{-8} {\rm eV}^2$, what is consistent rather with the LOW MSW solar solution. Thus, the favored LMA MSW estimation of $Δm_{21}^2$ might be a signal from the Dirac nature of neutrinos.8 pages, latex, no figuresHigh Energy Physics - Phenomenologytext