68 THE PRINCIPLES OF HEREDITY 



the mother, in the great majority of instances the children 

 will be more like ordinary men and women of their race than 

 either parent. In other words, there may be exclusive 

 inheritance, but more often there will be particulate, and 

 especially blended, inheritance. Only very exceptionally will 

 the child of such parents display a progressive variation that 

 is, be taller or darker than the father or shorter or fairer than 

 the mother. 



113. In this case, then, the combination of dissimilar germ- 

 plasms commonly results, not in progressive variations, but in a 

 regression towards the parental, and therefore the specific, 

 mean. But a regression towards the specific mean implies a 

 lapsing of progressive variations, and a lapsing of progressive 

 variations implies a failure in recapitulation, a reversion to the 

 ancestral type. Suppose, again, a man with a short thick 

 nose mates with a woman with a high thin nose; do we 

 commonly get a new and extraordinary type of nose as the 

 result a nose such as the current theory of the origin of 

 progressive variations would lead us to expect ? No. Again 

 there is reversion. The exceptional peculiarities of the parents 

 tend to disappear. Suppose, yet again, that a man with a sixth 

 digit mates with a normal woman. Do the offspring usually 

 have a seventh digit or any other exceptional peculiarity? 

 Assuredly not. Once again the general tendency is towards 

 a return to the specific, the ancestral type ; in one or more 

 generations the sixth digit tends to disappear. We may run 

 through the whole gamut of progressive variations and we shall 

 constantly get the same result. In every instance there is a 

 tendency to reversion, which is generally to the immediate 

 ancestors, but which may be to remoter ancestors, as when a 

 bird resembling Colnmba livia arises in the dovecot, or when 

 pure white sheep have dark-coloured offspring, or when a 

 cultivated plant reverts to the wild type. 



114 But now suppose two people mate who have the same 

 progressive variations who, for example, are both tall and 

 dark or short and fair, or who both have noses of the same 

 peculiar shape, or who have each a sixth digit what then is 

 the usual result ? Universal experience tells us that in such 

 cases the children tend to inherit the progressive variations which 

 the parents possess in common. They tend to be tall and dark, 

 or short and fair, and so forth. So that we may lay it down 

 as a general rule that bi-parental reproduction tends to eliminate 

 the characters in which parents differ, and to leave unaffected 

 those in which they agree. It follows that we have every 

 reason to believe that whenever bi-parental reproduction acts 



