APRIL I, 1897 | 
NATURE 
509 
good in case all the individuals of the species lay upon the left 
side, then (if I rightly understand the meaning of the terms), 
natural selection cannot be the cause of its lying on the right 
side rather than the left, neither can this character of the species 
be considered a useful character, though it is persistently 
inherited. 
Standing near me is a flower-pot, in which are several stalks 
of the common calla (I believe the botanical name is Rzchardia 
ethiopica) in bloom ; and a little inspection shows that each 
spathe and leaf-bud is twisted in the same way. If the leaf is 
held with the point up, and the upper surface toward you, the 
half of the leat on your left is the part that formed the inside of 
the leaf-bud, and the margin of the leaf on your right is the part 
that formed the outside of the leaf-bud This character is quite 
persistent in the specimens of this species found in this city, 
though I am told that a leaf twisted in the opposite way some- 
times appears ; whilein the distinct species, popularly called the 
black calla, I believe the character is reversed. Now, does this 
persistence prove that the character in question is essential to 
the welfare of the species? Are we justified in assuming that 
natural selection is the cause of the persistence of such character- 
istics ? Can any one throw light on the subject that will make 
it easier to believe that the adaptation of the species would be 
in the least impaired if all the leaves and spathes were twisted 
in the reverse way ? 
The usual method of meeting the natural inference from such 
cases is based on a double assumption, the first part of which is 
that natural selection is the only intelligible explanation of the 
modification of species or the persistence of character that has 
ever been given, and that, ifin any case we abandon this explana- 
tion, it is equivalent to abandoning all explanations ; the second 
part of the assumption being that it is simply our ignorance of 
the facts that prevents us from recognising the life-preserving 
results that are gained by the characteristic in question. This 
assumption ignores both the fact that species presenting 
character of the kind referred to are found on every side, indeed 
that almost every species that fails to maintain complete 
symmetry of form is an example, and the fact that Darwin him- 
self pointed out another principle beside natural selection pro- 
ducing persistent characters. This principle of sexual selection 
he carefully distinguished from natural selection, showing that 
the results produced by it could never be produced by natural 
selection, and even maintaining that ‘‘ It is not surprising that a 
slightly injurious character should have been thus acquired ” 
(** The Descent of Man,” 2nd ed., p. 601). 
For my part, Ido not think much progress can be made in 
discovering where natural selection is the chief agent, and where 
it is not the chief agent, till we have carefully defined what we 
mean by utility and natural selection, and then adhere to our 
definitions. ‘In my papers on ‘‘ Divergent Evolution through 
Cumulative Segregation” and ‘Intensive Segregation” (the 
former published in the Lixnean Society's Jcurn.—Zoology, 
vol. xx. ; the latter in the same, vol. xxiii.), I have endeavoured 
to show that there must be several principles somewhat similar 
to sexual selection, which I have grouped with it under the 
names reflexive segregation and reflexive selection. In the 
former of these papers, pp. 212-214, I have pointed out that 
“OF freely crossing forms of any species it is only those that 
are most successful that are perpetuated ; while of forms that 
are neither competing nor crossing, every kind is perpetuated 
that is not fatally deficient in its adaptations ” ; and this will be 
the case whether the forms are held apart by reflexive, or 
-environal segregation. 
Let us consider the case of two allied species occupying the 
same area, and differing from each other in what Dr. Wallace 
_ has so appropriately called their recognition marks, and in the 
segregating sexual and social instincts correlated with these 
marks. If investigation justifies the belief that an early stage of 
‘divergence, due, perhaps, to local segregation, resulted not only 
in sexual and social segregation, but also in what I have called 
divergent social selection (or what Dr. Wallace prefers to call 
selective association), then we are warranted in the belief that 
this segregative and selective principle was sufficient to perpetuate 
‘and intensify the new character, although the section of the 
species possessing the new character had not migrated into any 
new environment, and had not been exposed to any change in 
the old environment, and although it had not gained any new 
adaptation to the common environment of the two sections, 
and, therefore, while both sections of the species were equally 
subject to identical forms of natural selection. 
Now, seeing that the individuals of the segregated sections are 
NO. 1431, VOL. 55] 
able to find and keep company with associates, and in the season 
to pair with suitable mates, as affectually, but no more effec- 
tually, than before they were segregated, what shall we say of 
the usefulness of the distinctive characters that produce the 
segregation ? It is plain that these divergent characters are in 
constant use ; but does that prove that the divergence is a 
useful divergence ? Is it not possible that there should be a 
difference in use, which is not a useful difference? and if 
nothing has been gained by the difference either in main- 
taining the conditions of individual life, or in propagating 
the species, how can we call it a useful difference? And how 
can we attribute the divergence to natural selection, seeing 
natural selection is the superior maintenance and propagation 
of those better adapted to maintain life under the conditions 
surrounding the species ? 
I maintain that this reflexive segregation through the sexual 
and social instincts of the divergent sections of the species, is the 
firs\ in a series of divergent characters which may become a 
great advantage to both sections of the species, by enabling 
them to become adapted to different kinds of resources, 
requiring incompatible adaptations ; but it cannot be claimed 
that the usefulness to which this segregative character may 
attain in the future, or may have already attained, was the 
cause of the divergence which was steadily perpetuated, being 
intensified by sexual and social selection, and so completed 
while as yet this character was of no service to the species. 
The segregative character is preserved by its segregativeness, 
though at the time it arises, and for many subsequent gener- 
ations, it may not be of any advantage to its possessors. In 
most such cases, I believe, the initial divergence is gained by 
a local variety, in some measure protected by local segregation ; 
but having gained a character which secures segregation, even 
when commingled with the other section of the original species, 
it is no longer liable to be swamped by crossing. It seems to 
me that such cases are examples of divergence, produced by 
segregate breeding, brought about by sexual and social segre- 
gation, reinforced and strengthened by sexual and social selec- 
tion, and not by diversity in the action of natural selection. 
Another fundamental distinction, that needs to be kept in 
mind, is that diversity in the action of natural selection on 
segregated sections of a species may be due to three classes of 
causes, which are the real causes of the divergence, which 
results in the production of different species. 
(1) Different life-supporting and life-endangering conditions 
existing in the different districts in which the different sections 
of the species are distributed. 
(2) Different methods of using resources and escaping dangers, 
adopted by the different sections, though occupying the same 
district. 
(3) Different methods of using resources, and escaping dangers, 
adopted by the different sections of the species occupying 
isolated districts, whose resources and dangers are alike, 
If the members of the original species are brought under the 
influence of the first class of causes, it is due to diversity in 
the environments to which migration introduces them ; if under 
the second class, it is due to diversity in the action of life- 
preserving habits, while competing with each other ; if under 
the third class, it is due to diversity in this second respect, 
while not competing with each other. : 
Now, in some of the cases in the second class and in all 
those of the third class, it is impossible that the differences 
should be useful. This is most easily shown as regards the 
third class; for if in any case a new character attained by one 
of the sections is an advantage, then the same character would 
be an advantage for each of the other sections, exposed to the 
same conditions in other regions, and, therefore, there is no 
advantage in the difference. A 
If my thought is correct, some of the differences produced 
by diversity in the action of the several forms of reflexive segre- 
gation and selection, and all those produced by diversity in the 
action of natural selection, when that diversity is due to different 
habits that are not necessitated by any difference in the en- 
vironment, are non-useful differences. Therefore, beside the 
principle of ‘‘ correlated variation” referred to by Prof. Lan- 
kester (NATURE, vol. liv. pp. 245, 365), we have other ex- 
planations of certain kinds of specific characters that are not 
useful ; but the class of characters, of which right-handedness 
and left-handedness are examples, seem to lie beyond the reach 
of these explanations, and perhaps beyond the reach of the 
explanation suggested by Prof. Lankester. 
15 Concession, Osaka, Japan. Joun T. GULICK. 
