  New experimental results, if correct, require at least one light sterile
neutrino, in addition to the three active ones, to accommodate the mass
differences required to explain the solar $\nu_e$ deficit, the anomalous
$\nu/e$ ratio produced by atmospheric neutrinos, and either the candidate
events for $\nu_\mu\to\nu_e$ (or $\bar\nu_\mu\to\bar\nu_e$) from the LSND
experiment, or the possible need for a hot component of dark matter. This
neutrino mass pattern can not only accommodate all these four requirements, but
also provide a robust solution to a problem presently making heavy-element
synthesis by supernovae impossible and resolve a possible discrepancy between
big bang nucleosynthesis theory and observations.
