Several lines of theoretical and empirical evidence suggest that there can be a positive correlation between alpha diversity (genus richness) of marine communities (D) and average longevity of marine genera included in these communities (L). One possible reason for such a correlation is that diversity can be expected to give rise to ecosystem stability, which, in turn, may slow down the extinction of taxa. However, this hypothesis has not been verified on the global scale. The analysis of two large data sets (Sepkoski's compendium of fossil marine genera and the Paleobiology Database) shows that the correlation (1) actually exists and (2) is robust to some possible sources of errors in L and D estimation. Further analysis reveals that the correlation is not a secondary pattern caused by any of the following factors: (1) encounter probability of taxa, which is greatly influenced by differential incompleteness of the fossil record; (2) degree of sediment lithification, which is one of the major factors affecting the preservation of fossils; (3) onshore-offshore gradient; (4) parallel growth of both L and D through the Phanerozoic; (5) paleolatitudinal gradient. Although there may be other factors that influence both L and D in a similar way, the results generally confirm the hypothesis that higher alpha diversity enhances longevity of genera.