Why did Edmund Leach interpret Trobriand beliefs about conception as religious beliefs?

Edmund Leach interpreted Trobriand beliefs regarding human conception as religious rather than biological statements to distinguish them from pragmatic, everyday knowledge.1

While Trobrianders acknowledged the connection between sexual intercourse and procreation in animals, they maintained that human pregnancy resulted from the action of ancestral spirits. Leach argued that these assertions should be understood in the same manner as Christian beliefs concerning the Virgin Birth. By framing these claims as religious, he suggested they existed on a metaphysical plane outside the spectrum of ordinary experience.1

This interpretation allowed anthropologists to reconcile the Trobrianders' apparent denial of biological paternity with their practical intelligence, positing that they were not ignorant of the facts of reproduction but were instead making symbolic, religious statements that functioned at a different level of meaning.1