AUGUST 20, 1914] 
jungle-fowl. So we are taught; but try to recon- 
struct the steps in their evolution and you realise your 
hopeless ignorance. To be sure there are breeds, 
such as black-red game and brown leghorns, which 
have the colours of the jungle-fowl, though they 
differ in shape and other respects. As we know so 
little as yet of the genetics of shape, let us assume 
that those transitions could be got over. Suppose, 
further, as is probable, that the absence of the 
maternal instinct in the leghorn is due to loss of one 
factor which the jungle-fowl possesses. So far we 
are on fairly safe ground. But how about white 
leghorns? ‘Their origin may seem easy to imagine, 
since white varieties have often arisen in well-authen- 
ticated cases. But the white of white leghorns is not, 
as white in nature often is, due to the loss of the 
colour-elements, but to the action of something which 
inhibits their expression. Whence did that something 
come? The same question may be asked respecting 
the heavy breeds, such as Malays or Indian game. 
Each of these is a separate introduction from the East. 
To suppose that these, with their peculiar combs and 
close feathering, could have been developed from pre- 
existing European breeds is very difficult. On the 
other hand, there is no wild species now living any 
more like them. We may, of course, postulate that 
there was once such a species, now lost. That is 
quite conceivable, though the suggestion is purely 
speculative. I might thus go through the list of 
domesticated animals and plants of ancient origin 
and again and again we should be driven to this 
suggestion, that many of their distinctive characters 
must have been derived from some wild original now 
lost. Indeed, to this unsatisfying conclusion almost 
every careful writer on such subjects is now reduced. 
If we turn to modern evidence the case looks even 
worse. The new breeds of domestic animals made 
in recent times are the carefully selected products of 
recombination of pre-existing breeds. Most of the 
new varieties of cultivated plants are the outcome of 
deliberate crossing. There is generally no doubt in 
the matter. We have pretty full histories of these 
crosses in gladiolus, orchids, cineraria, begonia, 
calceolaria, pelargonium, etc. A very few certainly 
arise from a single origin. The sweet pea is the 
clearest case, and there are others which I should 
name with hesitation. The cyclamen is one of them, 
but we know that efforts to cross cyclamens were 
made early in the cultural history of the plant, and 
they may very well have been successful. Several 
plants for which single origins are alleged, such as 
the Chinese primrose, the dahlia, and tobacco, came 
to us in an already domesticated state, and their 
origins remain altogether mysterious. Formerly 
single origins were generally presumed, but at the 
present time numbers of the chief products of domes- 
tication, dogs, horses, cattle, sheep, poultry, wheat, 
oats, rice, plums, cherries, have in turn been accepted 
as ‘‘polyphyletic’’ or, in other words, derived from 
several distinct forms. The reason that has led to 
these judgments is that the distinctions between the 
chief varieties can be traced as far back as the 
evidence reaches, and that these distinctions are so 
great, so far transcending anything that we actually 
know variation capable of effecting, that it seems 
pleasanter to postpone the difficulty, relegating the 
critical differentiation to some misty antiquity into 
which we shall not be asked to penetrate. For it 
need scarcely be said that this is mere procrastination. 
If the origin of a form under domestication is hard 
to imagine, it becomes no easier to conceive of such 
enormous deviations from type coming to pass in the 
wild state. Examine any two thoroughly distinct 
species which meet each other in their distribution, 
NO. 2338, VOL. 93] 
NATURE 
639 
as, for instance, Lychnis diurna and vespertina do. 
In areas of overlap are many intermediate forms. 
These used to be taken to be transitional steps, and 
the specific distinctness of vespertina and diurna was 
on that account questioned. Once it is known that 
these supposed intergrades are merely mongrels be 
tween the two species the transition from one to the 
other is practically beyond our powers of imagination 
to conceive. If both these can survive, why has their 
common parent perished? Why when they cross do 
they not reconstruct it instead of producing partially 
sterile hybrids? I take this example to show how 
entirely the facts were formerly misinterpreted. 
When once the idea of a true-breeding—or, as we 
say, homozygous—type is grasped, the problem of 
variation becomes an insistent oppression. What can 
make such a type vary? We know, of course, one 
way by which novelty can be introduced—by crossing. 
Cross two well-marked varieties—for instance, of 
Chinese Primula—each breeding true, and in the 
second generation by mere recombination of the 
various factors which the two parental types severally 
introduced, there will be a profusion of forms, utterly 
unlike each other, distinct also from the original 
parents. Many of these can be bred true, and if 
found wild would certainly be described as good 
species. Confronted by the difficulty I have put 
before you, and contemplating such amazing poly- 
morphism in the second generation from a cross in 
Antirrhinum, Lotsy has lately with great courage 
suggested to us that all variation may be due to such 
crossing. I do not disguise my sympathy with this 
effort. After the blind complacency of conventional 
evolutionists it is refreshing to meet so frank an 
acknowledgment of the hardness of the problem. 
Lotsy’s utterance will at least do something to expose 
the artificiality of systematic zoology and botany. 
Whatever might or might not be revealed by experi- 
mental breeding, it is certain that without such tests 
we are merely guessing when we profess to distin- 
guish specific limits and to declare that this is a 
species and that a variety. The only definable unit in 
classification is the homozygous form which breeds 
true. When we presume to say that such and such 
differences are trivial and such others valid, we are 
commonly embarking on a course for which there is 
no physiological warrant. Who could have foreseen 
that the apple and the pear—so like each other that 
their botanical differences are evasive—could not be 
crossed together, though species of Antirrhinum so 
totally unlike each other as majus and molle can be 
hybridised, as Baur has shown, without a sign of 
impaired fertility? Jordan was perfectly right. The 
true-breeding forms which he distinguished in such 
multitudes are real entities, though the great 
systematists, dispensing with such laborious analysis, 
have pooled them into arbitrary Linnean species, for 
the convenience of collectors and for the simplification 
of catalogues. Such pragmatical considerations may 
mean much in the museum, but with them the student 
of the physiology of variation has nothing to do. 
These ‘‘little species,” finely cut, true-breeding, and 
innumerable mongrels between them, are what he 
finds when he examines any so-called variable type. 
On analysis the semblance of variability disappears, 
and the illusion is shown to be due to segregation and 
recombination of series of factors on pre-determined 
lines. As soon as the ‘‘little species’? are separated 
out they are found to be fixed. In face of such a re- 
sult we may well ask with Lotsy, is there such a 
thing as spontaneous variation anywhere? His 
answer is that there is not. 
Abandoning the attempt to show that positive 
factors can be added to the original stock, we have 
