What is a Variation? 95 
conclusion will bear the test of further research. To Darwin the 
question, What is a variation? presented no difficulties. Any difference 
between parent and offspring was a variation. Now we have to be 
more precise. First we must, as de Vries has shown, distinguish real, 
genetic, variation from fluctuational variations, due to environmental 
and other accidents, which cannot be transmitted. Having excluded 
these sources of error the variations observed must be expressed in 
terms of the factors to which they are due before their significance 
can be understood. For example, numbers of the variations seen 
under domestication, and not a few witnessed in nature, are simply 
the consequence of some ingredient being in an unknown way omitted 
from the composition of the varying individual. The variation may 
on the contrary be due to the addition of some new element, but to 
prove that it is so is by no means an easy matter. Casual observation is 
useless, for though these latter variations will always be dominants, yet 
many dominant characteristics may arise from another cause, namely 
the meeting of complementary factors, and special study of each case 
in two generations at least is needed before these two phenomena can 
be distinguished. 
When such considerations are fully appreciated it will be realised 
that medleys of most dissimilar occurrences are all confused together 
under the term Variation. One of the first objects of genetic analysis 
is to disentangle this mass of confusion. 
To those who have made no study of heredity it sometimes 
appears that the question of the effect of conditions in causing 
variation is one which we should immediately investigate, but a little 
thought will show that before any critical inquiry into such possi- 
bilities can be attempted, a knowledge of the working of heredity 
under conditions as far as possible uniform must be obtained. At 
the time when Darwin was writing, if a plant brought into cultivation 
gave off an albino variety, such an event was without hesitation 
ascribed to the change of life. Now we see that albino gametes, 
germs, that is to say, which are destitute of the pigment-forming 
factor, may have been originally produced by individuals standing an 
indefinite number of generations back in the ancestry of the actual 
albino, and it is indeed almost certain that the variation to which the 
appearance of the albino is due cannot have taken place in a genera- 
tion later than that of the grandparents. It is true that when a new 
dominant appears we should feel greater confidence that we were 
witnessing the original variation, but such events are of extreme 
rarity, and no such case has come under the notice of an experi- 
menter in modern times, as far as I am aware. That they must have 
appeared is clear enough. Nothing corresponding to the Brown- 
breasted Game fowl is known wild, yet that colour is a most definite 
