Note 331 — Chapter VII · —Geographical Boundaries

The distribution of animals and races shows the limit of their movements or expansion. Any boundary defining the limits of such movements can not from its nature be fixed, and hence can not be a line. It is always a zone. Yet "Wallace's Line," dividing the Oriental from the Australian zoological realm, and running through Macassar Strait southward between Bali and Lombok, is a generally accepted dictum. The details of Wallace's investigation, however, reveal the fact that this boundary is not a line, but a zone of considerable and variable width, enclosing the line on either side with a marginal belt of mixed character. Though Celebes, lying to the east of Macassar Strait, is included in the Australian realm, it has lost so large a proportion of Australian types of animals, and contains so many Oriental types from the west, that Wallace finds it almost impossible to decide on which side of the line it belongs.331 The Oriental admixture extends yet farther east over the Moluccas and Timor. Birds of Javan or Oriental origin, to the extent of thirty genera, have spread eastward well across Wallace's Line; some of these stop short at Flores, and some reach even to Timor,332 while Australian cockatoos, in turn, have been seen on the west coast of Bali but not in Java, Heilprin avoids the unscientific term line, because he finds his zoological realms divided by "transition regions," which are intermediate in animal types as they are in geographical location.333 Wallace notes a similar "debatable land" in the Rajputana Desert east of the Indus, which is the border district between the Oriental and Ethiopian realms.334