It is yet to be determined how the Grimm are created and how they reproduce. The current hypothesis is that they are mutated from a basic form by exposure to a powerful mutagen or mutagens. All captured Grimm have possessed no reproductive organs, leading to the conclusion that only a few representatives of the species if any are able to reproduce, and that their whole culture is built around the idea of protecting and sustaining these few.
Contrary to popular belief, Grimm are not led by a hive mind and do not possess any telepathic link to each other. They are a highly specialized society of experts (even if such expertise is for smashing human heads with clubs) and advance through feats and accomplishments in their fields. The more advanced Grimm are called alphas, but unlike in most species, alphas do not fight for supremacy – they hand it over to the most evolved individual. Currently, they are led by a human, John Grimmsham and it is probably so because they perceive him as a highest evolutionary form of Grimm – a multi-tasker.