Buoyed by Christian idealism, Oldham and his admirers in Australia and the Pacific region saw no reason why difference should lead to hostility. Rather than countering scientific determinism on its own terms, Oldham, Paton, and Burton opposed it on ethical grounds, based in the Christian belief in the essential unity of humankind. Although their writing did not move away entirely from notions of racial hierarchy, it reframed them in the language of obligation. While arguments based on moral and humanitarian grounds were explicitly denounced by biological determinists, missionary writers drawing on them were able to appeal to a new authority — that of the League of Nations and a new internationalism. This had considerable resonance in Australia as the new mandate over New Guinea triggered reflection within and beyond missionary circles. Attempting to engage a secular as well as a religiously committed audience, missionaries and other humanitarians employed the discourse of international relations and the associated new science of economics to further their constant message of Christian humanism as the principle which should guide relations with the Pacific Islands and with Pacific Islanders.