CHAPTER V 



THE LIMITS OF HEREDITY 



Another subject of great interest in connection with 

 human inheritance is the question of its hniits. 

 Are there any details of structure so small, or of such 

 a nature, as to be beyond the reach of heredity ? 

 Galton considered this subject, and in his book on 

 Finger Prints (1892) found such structures in the 

 more minute details or minutiae of the individual 

 ridges of the finger-print patterns.* We have already 

 considered another case (p. 74) in right and left- 

 handedness of cereals. Obviouslv the observation 

 of human duplicate twins should throw much light 

 on this subject, and since Galton 's studies, in which 

 he classified finger-tip patterns as loops, whorls, and 

 arches, a considerable literature has grown up which 



* I cannot refrain from pointing out again how closely Galton 's 

 views agreed with some of the current conceptions of continuous 

 and discontinuous variation. He says [I.e., p. 211): "Not only 

 is it impossible to substantiate a claim for natural selection, that 

 it is the sole agent in forming genera, but it seems, from the 

 experience of artificial selection, that it is scarcely competent to 

 do so by favouring mere varieties, in the sense in which I under- 

 stand the term. 



"My contention is that it acts by favouring small sports. 

 Mere varieties from a common typical centre blend freely in the 

 offspring, and the offspring of every race whose statistical charac- 

 ters are constant, necessarily tend, as 1 have often shown, to 

 regress towards their common typical centres. Sports, on the 

 other hand, do not blend freely; they are fresh typical centres 

 or sub-species, which suddenly arise, we do not yet know precisely 

 through what uncommon concurrence of circumstances, and which 

 observations show to be strongly transmissible by inheritance." 



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