JuLy 16, 1897.] 
they were then known to science. If they 
are mutable, it was argued, how would it 
be possible to separate so many which are 
known as perfectly distinct and not even 
capable of crossing so as to mix one with 
another. Sterility was seen to be an im- 
passable barrier distinguishing one species 
from another, and, as the individuals of 
one generation are to be accounted for only 
as descendants of a ‘previous one, how 
would it be possible to make this barrier 
on the theory that the law of each species 
is not fixed and immutable? But although 
the theory of mutability of species was 
thought to be absurd a century ago, and 
was supposed to contradict the fundamen- 
tal principles of natural history, the idea of 
specific mutability has now become an es- 
tablished truth in our philosophy of or- 
ganisms, and variability, or the power of 
the organism to divert from the current 
paths of development of its ancestors, has 
become the important factor in evolution. 
We find, in fact, Bateson, in his elaborate 
treatise on variation,* saying: ‘“ Variation 
whatever may be its cause, and however it 
may be limited, is the essential phenome- 
non of evolution; variation, in fact, is evo- 
lution ”’ (p. 6). 
When we follow up the history a step 
further we discover that the theory of 
mutability of species is built directly upon 
the Cuvierian philosophy, butit is by break- 
ing down the distinction between varieties 
and species as originally understood. 
Lamarck and Darwin both accepted the 
old conception of the normal or funda- 
mental uniformity of the processes of gen- 
eration, but, recognizing the fact of depar- 
ture from this uniformity, assumed that the 
variation is due to the active adjustment 
by the organism of its structure to changed 
conditions of environment (Lamarck) ; or, 
*Materials for the study of variation treated with 
special regard to discontinuity in the origin of species, 
by Wim. Bateson. 1894. 
SCIENCE. 
75 
the variations being spontaneous or acci- 
dental, they are preserved and transmitted 
in generation from parent to off-spring 
(Darwin). 
Both schools and, so far as I have ob- 
served, the great majority of all those who 
discuss these problems, have started with 
the assumption that the normal province of 
what is called by the general name of re- 
production is the cyclical repetition of 
phenomena expressed in the ancestors, 7. ¢., 
that the phenomena will be alike unless 
some cause can be discovered for their dis- 
similarity. Hence to discover the cause of 
differences has been the chief purpose of 
observers and speculators. 
Darwin’s ideas regarding the nature of 
variability in organism are clearly set forth 
in his ‘Origin of Species.’ In the first chapter 
on ‘ Variation under Domestication,’ under 
the general title ‘ Causes of Variability,’ we 
find this significant sentence: ‘It seems 
pretty clear that organic beings must be 
exposed during several generations to the 
new conditions of life to cause any appre- 
ciable amount of variation, and that when 
the organization has once begun to vary it 
generally continues to vary for genera- 
tions” (p. 14). <A few sentences further 
on are these words: ‘It has been disputed 
at what period of life the causes of varia- 
bility act,” and “ I am strongly inclined to- 
suspect that the most frequent cause of 
variability may be attributed to the male 
and female reproductive elements having 
been affected prior to the act of conception,” 
and again : “‘ When any deviation of struc- 
ture often appears, and we see it in the 
father and child, we cannot tell whether it 
may not be due to the same cause having 
acted on both” (p. 19). Again in the 
chapter on ‘ Laws of Variation:’ ‘‘ Never- 
theless, we can, hereand there, dimly catch 
a faint ray of light, and we may feel sure 
that there must be some cause for each 
deviation of structure, however slight ” 
