We find that the globular cluster systems of the Milky Way and of our neighboring spiral galaxy, M31, comprise two distinct entities, differing in three respects. First, M31 has a set of young globular clusters (GCs), ranging in age from a few 100 Myr to 5 Gyr old, as well as old globular clusters. No such very young GCs are known in the Milky Way. Second, we confirm that the oldest M31 GCs have much higher nitrogen abundances than do Galactic GCs at equivalent metallicities. Third, Morrison et al. have shown that M31 has a subcomponent of GCs that follow closely the disk rotation curve of that galaxy. Such a GC system in our own Galaxy has yet to be found. The only plausible scenario for the existence of the young M31 GC comes from the hierarchical-clustering-merging (HCM) paradigm for galaxy formation. We infer that M31 has absorbed more of its contingent of dwarf systems in the recent past than has the Milky Way. This inference has three implications: First, that all spiral galaxies could differ in their globular cluster properties, depending on how many companions eac
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