AUGUST 20, 1914] 
not become part of the invaded host, and we cannot 
conceive it taking part in the geometrically ordered 
processes of segregation. These illustrations may 
seem too gross; but what refinement will meet the 
requirements of the problem, that the thing intro- 
duced must be, as the living organism itself is, 
capable of multiplication and of subordinating itself 
in a definite system of segregation? That which is 
conferred in variation must rather itself be a change, 
not of material, but of arrangement, or of motion. 
The invocation of additions extrinsic to the organism 
does not seriously help us to imagine how the power 
to change can be conferred, and if it proves that hope 
in that direction must be abandoned, I think we lose 
very little. By the re-arrangement of a very moderate 
number of things we soon reach a number of possi- 
bilities practically infinite. 
That primordial life may have been of small dimen- 
sions need not disturb us. Quantity is of no account 
in these considerations. Shakespeare once existed as 
a speck of protoplasm not so big as a small pin’s 
head. To this nothing was added that would not 
equally well have served to build up a baboon or a 
rat. Let us consider how far we can get by the 
process of removal of what we call ‘‘ epistatic’’ factors, 
in other words those that control, mask, or suppress 
underlying powers and faculties. I have spoken of 
the vast range of colours exhibited by modern sweet 
peas. There is no question that these have been de- 
rived from the one wild bi-colour form by a process of 
successive removals. When the vast range of form, 
size, and flavour to be found among the cultivated 
apples is considered it seems difficult to suppose that 
all this variety is hidden in the wild crab-apple. I 
cannot positively assert that this is so, but I think all 
familiar with Mendelian analysis would agree with 
me that it is probable, and that the wild crab con- 
tains presumably inhibiting elements which the culti- 
vated kinds have lost. The legend that the seedlings 
of cultivated apples become crabs is often repeated. 
After many inquiries among the raisers of apple 
seedlings I have never found an authentic case—once 
only even an alleged case, and this on inquiry proved 
to be unfounded. I have confidence that the artistic 
gifts of mankind will prove to be due not to some- 
thing added to the make-up of an ordinary man, but 
to the absence of factors which in the normal person 
inhibit the development of these gifts. They are 
almost beyond doubt to be looked upon as releases 
of powers normally suppressed. The instrument is 
there, but it is ‘‘stopped down.’’ The scents of 
flowers or fruits, the finely repeated divisions that give 
its quality to the wool of the merino, or in an 
analogous case the multiplicity of quills to the tail of 
the fantail pigeon, are in all probability other examples 
of such releases. You may ask what guides us in the 
discrimination of the positive factors and how we can 
satisfy ourselves that the appearance of a quality is 
due to loss. It must be conceded that in these deter- 
minations we have as yet recourse only to the effects 
of dominance. When the tall pea is crossed with the 
dwarf, since the offspring is tall we say that the tall 
parent passed a factor into the cross-bred which makes 
it tall. The pure tall parent had two doses of this 
factor; the dwarf had none; and since the cross-bred 
is tall we say that one dose of the dominant tallness 
is enough to give the full height. The reasoning 
seems unanswerable. But the commoner result of 
crossing is the production of a form intermediate 
between the two pure parental types. In such 
examples we see clearly enough that the full parental 
characteristics can only appear when they are homo- 
zvgous—formed from similar germ-cells, and that one 
dose is insufficient to produce either effect fully. When 
NO. 2338, VOL. 93] 
NATURE 
641 
this is so we can never be sure which side is positive 
and which negative. Since, then, when dominance 
is incomplete we find ourselves in this difficulty, we 
perceive that the amount of the effect is our only 
criterion in distinguishing the positive from the nega- 
tive, and when we return even to the example of the 
tall and dwarf peas the matter is not so certain as it 
seemed. Professor Cockerell lately found among 
thousands of yellow sunflowers one which was partly 
red. By breeding he raised from this a form whollv 
red. Evidently the yellow and the wholly red are the 
pure forms, and the partially red is the heterozygote. 
We may then say that the yellow is YY with two 
doses of a positive factor which inhibits the develop- 
ment of pigment; the red is yy, with no dose of the 
inhibitor ; and the partially red are Vy, with only one 
dose of it. But we might be tempted to think the 
red was a positive characteristic, and invert the ex- 
pressions, representing the red as RR, the partly red as 
Ry, and the yellow as rr. According as we adopt the 
one or the other system of expression we shall inter- 
pret the evolutionary change as one of loss or as one 
of addition. May we not interpret the other apparent 
new dominants in the same way? The white domi- 
nant in the fowl or in the Chinese primula can inhibit 
colour. But may it not be that the original coloured 
fowl or primula had two doses of a factor which in- 
hibited this inhibitor? The Pepper moth, Amphidasys 
betularia, produced in England about 1840 a black 
variety, then a novelty, now common in certain areas, 
which behaves as a full dominant. The pure blacks 
are no blacker than the cross-bred. Though at first 
sight it seems that the black must have been some- 
thing added, we can without absurdity suggest that 
the normal is the term in which two doses of inhibitor 
are present, and that in the absence of one of them 
the black appears. 
In spite of seeming perversity, therefore, we have 
to admit that there is no evolutionary change which in 
the present state of our knowledge we can positively 
declare to be not due to loss. When this has been 
conceded it is natural to ask whether the removal of 
inhibiting factors may not be invoked in alleviation 
of the necessity which has driven students of the 
domestic breeds to refer their diversities to multiple 
origins. Something, no doubt, is to be hoped for in 
that direction, but not until much better and more 
extensive knowledge of what variation by loss may 
effect in the living body can we have any real assur- 
ance that this difficulty has been obviated. We should 
be greatly helped by some indication as to whether the 
origin of life has been single or multiple. Modern 
opinion is, perhaps, inclining to the multiple theory, 
but we have no real evidence. Indeed, the problem 
still stands outside the range of scientific investiga- 
tion, and when we hear the spontaneous formation 
of formaldehyde mentioned as a possible first step 
in the origin of life, we think of Harry Lauder in 
the character of a Glasgow schoolboy pulling out his 
treasures from his pocket—‘‘ That’s a wassher—for 
makkin’ motor cars’’! 
As the evidence stands at present all that can be 
safely added in amplication of the evolutionary creed 
may be summed up in the statement that variation 
occurs as a definite event often producing a sensibly 
discontinuous result; that the succession of varieties 
comes to pass by the elevation and establishment of 
sporadic groups of individuals owing their origin to 
such isolated events; and that the change which we 
see as a nascent variation is often, perhaps always, 
one of loss. Modern research lends not the smallest 
encouragement or sanction to the view that gradual 
evolution occurs by the transformation of masses of 
individuals, though that faney has fixed itself on 
