d. II.
page 82.), and that he regarded as a mere counsel of despair:--"to make
continents, as easily as a cook does pancakes." (Ibid. II. page 74.)

The question of multiple origins however presented itself in another
shape where the solution was much more difficult. The problem, as
stated by Darwin, is this:--"The identity of many plants and animals,
on mountain-summits, separated from each other by hundreds of miles of
lowlands... without the apparent possibility of their having migrated
from one point to the other." He continues, "even as long ago as 1747,
such facts led Gmelin to conclude that the same species must have been
independently created at several distinct points; and we might have
remained in this same belief, had not Agassiz and others called vivid
attention to the Glacial period, which affords... a simple explanation of
the facts." ("Origin of Species" (6th edition) page 330.)

The "simple explanation" was substantially given by E. Forbes in 1846.
It is scarcely too much to say that it belongs to the same class of
fertile and far-reaching ideas as "natural selection" itself. It is
an extraordinary instance, if one were wanted at all, of Darwin's
magnanimity and intense modesty that though he had arrived at the theory
himself, he acquiesced in Forbes receiving the well-merited credit.
"I have never," he says, "of course alluded in print to my having
independently worked out this view." But he would have been more than
human if he had not added:--"I was forestalled in... one important point,
which my vanity has always made me regret." ("Life and Letters", I. page
88.)

Darwin, however, by applying the theory to trans-tropical migration,
went far beyond Forbes. The first enunciation to this is apparently
contained in a letter to Asa Gray in 1858. The whole is too long
to quote, but the pith is contained in one paragraph. "There is a
considerable body of geological evidence that during the Glacial epoch
the whole world was colder; I inferred that,... from erratic boulder
phenomena carefully observed by me on both the east and west coast of
South America. Now I am so bold as to believe that at the height of
the Glacial epoch, AND WHEN ALL TROPICAL PRODUCTIONS MUST HAVE BEEN
CONSIDERABLY DISTRESSED, several temperate forms slowly travelled into
the heart of the Tropics, and even reached the southern hemisphere; and
some few southern forms penetrated in a reverse direction northward."
("Life and Letters", I