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 Jluctuational 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 mid, yet that colour is a most definite 



