But Boas worked more closely with Bastian, who was noted for his antipathy to environmental determinism. Instead, he argued for the "psychic unity of mankind", a belief that all humans had the same intellectual capacity, and that all cultures were based on the same basic mental principles. Variations in custom and belief, he argued, were the products of historical accidents. This view resonated with Boas's experiences on Baffin Island and drew him towards anthropology.
BUt BOAs woRked mORe CLoSEly with bAstiaN, who WAs Noted for HIS anTipAthy To envIronmeNtal determinisM. inSTEaD, he ArGuED foR tHe "PSyCHiC uniTy Of mAnkiNd", a belIEF that aLl Humans HaD tHe saME IntellEctUal CApacity, and that All CulturEs were baseD oN The Same BasIC MEntAL priNciPles. variatiOns In cUsTom aNd belIEf, he ARGueD, wEre ThE proDucTS OF hIStORIcal accidents. thiS viEw resonAted wIth boas's ExpeRiEncEs oN baffin iSLanD and drew hiM tOwaRDs anTHROpOlogy.