Eusociality is the most successful animal social system on earth. It is found in many social insects, a few crustacean species, and only three vertebrates: two African naked mole rats and human beings. Eusociality, so unusual for a vertebrate, is one of main factors leading to human beings becoming the most successful land vertebrate on earth by almost any measure. We are also unique in being the only land vertebrate with religions. Could the two be related? This article will present (...) evidence, illustrated primarily with Judaism and Christianity, that these two seemingly unrelated social systems – eusociality and religion – that correlate temporally in our evolution, are possibly related. Evidence will also be presented that a non-reproducing exemplar caste of celibate clergy was a eusocial-facilitating aspect of religion in western social evolution. (shrink)