Complex Spinors and Unified Theories

In this paper delivered by Murray Gell-Mann at the Stony Brook Supergravity Workshop in 1979, several paths to unification are discussed, from N=8 supergravity to $S{U}_5$, $S{O}_{10}$, and $E_6$. Generalizations of $S{O}_{10}$ to spinor representations of larger groups are introduced. A natural mechanism for generating tiny neutrino masses is proposed in the context of $S{O}_{10}$, and finally, focus on $S{U}_3$ rather than $S{U}_2$ or $S{O}_3$ family symmetries is noted.