Multiple Origins 303 
the agency of birds; and when in explanation of the Scandinavian 
elements in the Spitzbergen flora he had to choose between a former 
land connection and the agency of birds, he preferred the bird}.” 
Darwin objected to “continental extensions” on geological grounds, 
but he also objected to Lyell that they do not “account for all the 
phenomena of distribution on islands’,” such for example as the 
absence of Acacias and Banksias in New Zealand. He agreed 
with De Candolle that “it is poor work putting together the merely 
possible means of distribution.” But he also agreed with him that 
they were the only practicable door of escape from multiple origins. 
If they would not work then “every one who believes in single 
centres will have to admit continental extensions’,” and that he 
regarded as a mere counsel of despair:—“to make continents, as 
easily as a cook does pancakes*.” 
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 
tniles 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 
...@ simple explanation of the facts®.” 
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®,” 
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 
1 Guppy, op. cit. u. pp. 511, 512. 2 Life and Letters, i. p. 77. 
3 Ibid. 1. p. 82. 4 Ibid. u. p. 74. 
> Origin of Species (6th ed.) p. 330. ® Life and Letters, 1. p. 88. 
