110 HEREDITARY CHARACTERS 



"regressive." The regressive variation may be briefly de- 

 scribed as the failure of some character present in the 

 parents to appear in the offspring. In the disappearance of 

 racial characters such as we have seen in organisms which 

 take to a parasitic mode of life, we have an example of the 

 disappearance of well-established characters. 1 Variations, 

 however, occur constantly, and the great majority of them 

 do not tend to produce new racial characters, although they 

 are capable of being transmitted from parent to offspring. 

 The majority of variations occurring in an individual are, 

 as we shall see later, generally eliminated in two or three 

 generations unless they are the subjects of selection. Thus, 

 regressive variations the disappearance in the offspring of 

 variations occurring in the parent must be quite as 

 frequent as progressive variations. It is necessary, in order 

 to obtain a clear conception of this phenomenon, to consider 

 very briefly some facts connected with the development of 

 the individual. 



We know that in the case of man, as in all multicellular 

 organisms, every individual commences existence as a single 

 cell the fertilised ovum. This cell divides, the daughter 

 cells again divide, and so the organism is built up. 2 In the 

 complicated process of development the cells produced are 

 at first arranged in two layers, then a third layer grows 

 between the first two, and by gradual and complicated but 

 orderly stages all the parts of a man are developed. The 

 same series of changes takes place in the development of 

 every normal human individual, so it is quite certain that 

 in man the same processes are gone through in the de- 

 velopment of the offspring that were gone through in the 

 development of the parent. The same thing happened in 

 the case of the parents, for they in their turn went through 

 the same series of changes in the process of development 

 that their parents went through before them. Thus, the 



1 See p. 66. 



2 The following theory of recapitulation has been formulated in detail by 

 Archdall Reid, The Principles of Heredity, 1905, p. 52 sqq. 



