JUNE 13, 1912] 
of discontinuity; in fact, fluctuation in the sense 
of plus and minus variation was not ‘recog- 
nised at the time; the notion of variation was 
that derived directly from field rather than from 
laboratory notes. 
The distinctive features of the later develop- 
ment of the theory in Wallace’s mind were his 
more implicit faith in it, his insistence on utility 
or selection value, his rejection of Lamarckism, his 
dependence on spontaneous variations as supply- 
ing all the materials for selection. This confidence 
appears in the following passages from his mili- 
tant reply in the volume of 1889 to the critics of 
Darwinism :—‘‘ The right or favourable varia- 
tions are so frequently present that the unerring 
power of natural selection never wants materials 
to work upon. . . . The importance of natural 
selection as the one invariable and ever-present 
factor in all organic change and that which can 
alone have produced the temporary fixity com- 
bined with the secular modification of species.”’ 
The principle of discontinuity is less clearly 
brought out; the selection of fluctuation is favour- 
ably considered. The laws and causes of varia- 
tion are, however, assumed rather than taken up 
as a subject of inquiry. These opinions of 1889 
were the summation of twenty-nine years of 
work. ‘ 
The colouring of animals as observed in the 
tropics and the Malayan Islands was the subject 
in which Wallace made his most extensive and 
original contributions to Darwinism. Returning 
from the Archipelago in 1862, he published in 1864 
his pioneer paper, “The Malayan Papilionide or 
Swallow Tailed Butterflies, as illustrative of the 
Theory of Natural Selection,’’ in which he at once 
took rank beside Bates and Miller as one of the 
great contributors to the colour characteristics 
of animals. We see him step by step developing 
the ideas of protective resemblance which he had 
fully discussed with Bates, of alluring and warn- 
ing colours, and of mimicry, pointing out the 
prevalence of mimicry in the female rather than 
in the male. The whole series of phenomena are 
believed to depend upon the great principle of 
the utility of every character, upon the need of 
colour protection by almost all animals, and upon 
the known fact that no characteristic is so variable 
as colour, that, therefore, concealment is most 
easily obtained by colour modification. Protec- 
tive resemblance in all its manifold forms has 
ever been dominant in his mind as a greater 
principle than that of the sexual selection of colour 
which Darwin favoured. 
NO. 2224, VOL. 89] 
NATURE 
3°9 
In 1867 Wallace advanced his provisional solu- 
tion of the cause of the gay and even gaudy 
colours of caterpillars as warnings of distasteful- 
ness in a manner which delighted Darwin; in 
1868 he propounded his explanation of the colours 
of nesting birds, that when both sexes are con- 
spicuously coloured, the nest conceals the sitting 
bird, but when the male is conspicuously coloured 
and the nest is open to view, the female is plainly 
coloured and inconspicuous. His theory of recog- 
nition colours as of importance in enabling the 
young of birds and mammals to find their parents 
was set forth in 1878, and he came to regard it 
as of very “© Tropical 
great importance. In 
| Nature ’’ (1878) the whole subject of the colours 
of animals in relation to natural and sexual selec- 
| tion is reviewed, and the general principle is 
brought out that the exquisite beauty and variety 
of insect colours has not been developed through 
their own visual perceptions, but mainly and per- 
haps exclusively through those of the higher 
animals which prey upon them. This conception 
of colour origin, rather than that of the general 
influence of solar light and heat or the special 
action of any form of environment, leads him to 
his functional and biological classification of the 
colours of living organisms into five groups, 
which forms the foundation of the modern more 
extensive and critical classification of Poulton. 
Twelve years later he devoted four chapters of 
his ‘‘ Darwinism ”’ to the colours of animals and 
plants, still maintaining the utility, spontaneous 
variation, and selection theory. 
The study of geographic distribution of animals 
also sprang from the inspiration of the Malayan 
journey and from the suggestiveness of the 
eleventh and twelfth chapters of ‘‘ The Origin of 
| Species ’’ which Wallace determined to work out 
in an exhaustive manner. Following the pre- 
liminary treatises of Buffon, of Cuvier and Forbes, 
| and the early regional classification of Sclater, 
Wallace takes rank as the founder of the science 
of zoogeography in his two great works, ‘‘ The 
Geographical Distribution of Animals’’ of 1576, 
and ‘‘ Island Life’’ of 1881, the latter volume 
following the first as the result of four years of 
additional thought and research. His early ob- 
servations on insular distribution were sketched 
out in his article of 1860, ‘‘ The Zoological Geo- 
graphy of the Malayan Archipelago.’’ Here is 
his discovery of the Bali-Lombok boundary line 
between the Indian and Australian zoological 
regions which has since been generally known hy 
his name. 
