 Lamarckians believed that environmental forces could precipitate rapid and enduring changes in organisms that had no inherited source; thus, Lamarckians and environmental determinists often found themselves on the same side of debates.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.