ARCHDALL REID ON RECAPITULATION 9 



viz., the recapitulation of the parent by the child, and, conse- 

 quently, of the life-history of the race by the individual. In 

 every normal individual in every individual who survives 

 the variations from the parent are as a drop in the ocean 

 compared with the likenesses. Were it otherwise, no organism 

 would reproduce its kind. . . . Every variation, when once it 

 has started, may be looked upon as a structure capable of 

 independent variation in an almost infinite number of 

 directions, regressive and progressive. As a consequence 

 every species of plant and animal is in a condition of 

 continual flux and change. As a whole the likeness to the 

 parent is well preserved. But in minutiae there is an immense 

 amount of variation. 



" Evolution is adaptive racial change. . . . ( Many instances 

 could be given to prove that progression and retrogression 

 are the two main principles of evolution at large ' (De Vries). 

 A progressive variation constitutes a deviation from the 

 parental and ancestral type, which, speaking generally, is in 

 the direction of increased magnitude and complexity. It 

 results from the complete recapitulation of the parental 

 development plus an addition. A regressive variation 

 constitutes a deviation from the parental towards the 

 ancestral type. As a rule it is in the direction of diminished 

 magnitude and complexity. It results from an incomplete 

 recapitulation of the parental development. . . . The tendency 

 to vary spontaneously has been evolved by Natural Selection. 

 Like any other character it may be increased or diminished 

 by the same agency, or by reversion to a more or less variable 

 ancestral type. Whenever a hitherto stable environment 

 changes, the tendency is increased. If the stringency of 

 selection is increased, the tendency to vary is exalted by 

 Natural Selection. If the stringency is diminished, the 

 tendency is exalted by reversion. In both cases adaptation 

 to the changing environment is hastened. . . . Every instance 

 of regression is a failure to recapitulate part of the parents' 

 development, and consequently part of the life-history. It is 

 therefore, of logical necessity, an instance of reversion. . . . 

 The remote ancestor of the modern horse, the Hipparion, had 

 three functional toes. The embryo of the horse has also 

 three toes of considerable size. But the two outer toes ot 

 each limb, which in the embryo are nearly as well developed 

 as in the Hipparion, degenerate partially during development, 

 so that the horse is born with only one functional toe. 

 Occasionally a foal is born with two hoofs on one limb. 

 When an outer toe persists, we have plainly, in a real sense, 

 an arrest of development. The toes remain in the embryo 



