s no way of shutting the
door against the possibility that these individuals may have been so
numerous that they occupied a very large district, even so large that
it had become as discontinuous as the distribution of many a species
actually is. Such a concession would at once be taken as an admission of
multiple, independent, origin instead of descent in Darwin's sense.

For the so-called multiple, independently repeated creation of species
as an explanation of their very wide and often quite discontinuous
distribution, he substituted colonisation from the nearest and readiest
source together with subsequent modification and better adaptation to
their new home.

He was the first seriously to call attention to the many accidental
means, "which more properly should be called occasional means of
distribution," especially to oceanic islands. His specific, even
individual, centres of creation made migrations all the more necessary,
but their extent was sadly baulked by the prevailing dogma of the
permanency of the oceans. Any number of small changes ("many islands
having existed as halting places, of which not a wreck now remains"
("The Origin of Species" (1st edition), page 396.).) were conceded
freely, but few, if any, great enough to permit migration of truly
terrestrial creatures. The only means of getting across the gaps was by
the principle of the "flotsam and jetsam," a theory which Darwin took
over from Lyell and further elaborated so as to make it applicable to
many kinds of plants and animals, but sadly deficient, often grotesque,
in the case of most terrestrial creatures.

Another very fertile source was Darwin's strong insistence upon the
great influence which the last glacial epoch must have had upon the
distribution of animals and plants. Why was the migration of northern
creatures southwards of far-reaching and most significant importance?
More northerners have established themselves in southern lands than
vice versa, because there is such a great mass of land in the north
and greater continents imply greater intensity of selection. "The
productions of real islands have everywhere largely yielded to
continental forms." (Ibid. page 380.)... "The Alpine forms have almost
everywhere largely yielded to the more dominant forms generated in the
larger areas and more efficient workshops of the North."

Let us now pass in rapid survey the influence of the publication of "The
Origin of Species" upon the study of G