  Operating 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 $\Delta m_{21}^2$ 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 $\Delta m_{21}^2$ 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 $\Delta m_{21}^2$ might be a signal from the Dirac nature
of neutrinos.
