1 2 2 Psychology and Ethnology.
If ethnology is to become a science, it must postulate that the same cause cannot produce different effects, and that every effect must be fully explained by the hypothesis, or the hypothesis is null and void. If a custom is founded on an instinct, it must occur wherever and whenever that instinct is present, or we must be able to point to the cause that is counteracting the instinct. If a custom is founded solely on an instinct, every detail of that custom must be deducible from that instinct.
What should we think of a technologist who explained all the manifold methods of fishing, hunting and planting by the instinct of hunger? Yet I cannot see that he would be ex- plaining less than a sociologist, who would deduce all the varieties of exogamy from sexual jealousy, or the countless forms of totemism from confusion of identity or fear of animated nature.
Even assuming instinct to be at the bottom of all custom, yet that would not help us one atom. For the instincts of man do not form a harmonious body, but a struggling mass of competing impulses ; so that even if we could prove that a certain custom is a manifestation of a certain instinct, we should still have to explain why that particular instinct was allowed to come into play at all, and was not suppressed by its rivals. And this explanation can only lie in the historical antecedents.
For instance, over the greater part of the world, it would appear, it is the custom for the man to court and propose. The fact seems to require no explanation : it is the law of the animal world for the male to court and the female coyly to assent. And yet in parts of the Solomons it is quite common for the girl to propose : in the Western Torres Straits Islands^ it is even considered improper for the young man to propose, or to accept the young girl's proposal with too much eagerness. Here then the instinct has been completely set at naught, and not by any other instinct that ^Reports of the Cambridge Expedition to Torres Straits, vol. v., pp. 222 ff.