101. Cultural Context
The presence or absence of other connections is also a factor of greatest importance. In other words, no fact relating to human civilization may be judged wholly without reference to its context or background. If there are known connections, either in space or in time, between two nations, the likelihood of their having separately evolved a common trait is much less than as between two peoples in different continents or separated by thousands of years. It is not known precisely how knowledge of the true arch and of liver divination were carried from ancient western Asia to the Etruscans of Italy. Yet the fact that Babylonia and Etruria shared two such specific culture traits as these, greatly increases the probability for each one having been borrowed from the Asiatic by the European people. When the consideration is added that the ancients had traditions of the Etruscans having come to Italy out of Asia Minor, the likelihood of diffusion is strengthened to the point of practical certainty.
Connection in space is a particularly cogent argument in favor of diffusion, because of its powerful presumption of accompanying communication. When several hundred Indian tribes without a break in their ranks between Quebec and Argentina cultivate maize, it would be absurd to dream of each of them having originated the domestication of the plant for itself. To be sure, it is logically conceivable that maize agriculture was independently developed by two or three of the most advanced tribes of the hundreds and then became diffused until the two or three areas of dispersion met and coalesced into one greater area. Yet the principle that economy of explanation is the best would militate even against this interpretation as compared with diffusion from a single center, unless there were definite indications in favor of the multiple origin explanation. Such indications might be radically distinct types of the plant or of agricultural implements in several parts of the maize area.
So, when the tribes on the Alaskan and Siberian sides of Behring Sea relate similar Raven legends, the geographical proximity is so close that it would be pedantic to let the fact that two continents are involved stand in the way of an explanation by diffusion. Even where the distribution of a trait penetrates much farther into both America and Asia, as is true of the composite bow (ยง [210]), the continuity of area leaves little doubt as to diffusion from a single center, especially since it is reinforced by other traits showing the same intercontinental distribution: the Magic Flight story, for instance. It is only when the areas are discrete as well as remote, when other similarities between them are few or absent, when their cultural backgrounds are radically dissimilar, as in the case of the couvade, that parallelism begins to knock at the door of interpretation with serious hope of admittance.