128 HEREDITARY CHARACTERS 



best, and so will have the best chances of producing offspring 

 in their turn. In the next generation we might conceivably 

 get individuals with 6A+4X. In any case, if selection went 

 on in favour of A for a large number of generations, it would 

 seem that we ought theoretically to end with 10 A. Without 

 selection, however, the chances of A being preserved are 

 exceedingly small. Even supposing a large proportion of 

 the entities were represented by the variation A, and some 

 other favourable variation B were the subject of selection 

 while A ceased to be the subject of selection, A would 

 certainly be eliminated in favour of B. 



Thus, there does not appear to be any material objection 

 to the assumption that individual chromosomes or parts of 

 chromosomes represent individual variations, and on this 

 hypothesis the effect of bi-parental reproduction must be to 

 eliminate all those variations which are not the subject of 

 selection. 



This problem the effect of bi-parental reproduction 

 has been approached in quite a different way, and similar 

 conclusions have been arrived at by Archdall Reid. 1 He 

 begins by citing examples which must have come within 

 the experience of every one. He points out that the off- 

 spring of parents differing from each other materially, are 

 generally more like the average of the race than like either 

 of the parents. " The exceptional peculiarities of the parents 

 tend to disappear." If two people both possessing the same 

 peculiarity mate, however, " the children tend to inherit the 

 progressive variations which the parents possess in common." 

 If varieties or species are crossed, instead of new variations 

 being produced, there is generally a great tendency towards 

 reversion, that is, to the non-appearance of some of the char- 

 acters of one or both parents. If a Burchell zebra is mated 

 with a horse, " some of the hybrids in make and disposition 

 strongly suggest their zebra sire, others their respective dams, 

 but even the most zebra-like in form are entirely unlike their 

 sire in their markings. It is not a matter of taking after the 



1 Principles of Heredity. 



