User blog comment:Arbington/The Next Cycle/@comment-5267262-20120803203730/@comment-2250460-20120803205335

I am 100% certain it is mentioned somewhere (It may have been by someone working for Bioware on BSN) that the Reapers pick one race to transform in Sovereign-Class Reapers i.e. humans, and that the "lesser" races are turned into destroyers.