VARIATIONS 113 



place in connection with the reduction division, where 

 during synapsis certain character-determining units in 

 the chromosomes may become exclianged, so that the 

 chances are about equal whether one or the other char- 

 acter from respectively one or the other parent will be 

 present in the new cell. Mendel found that about one- 

 fourth of the second generation plants show a given char- 

 acter from one of the original plants and one-fourth the 

 character from the other plant, while one-half stiU re- 

 tains (at least potentially) both characters, although only 

 one is visible, it being "dominant" over the other char- 

 acter which is "recessive." That both characters are 

 present is shown by the fact that seeds from this half 

 produce plants which divide up again into one-fourth, 

 one-fourth, and one-half, etc. 



164. In sexual reproduction the various differences 

 borne by the different chromosomes, or ■ perhaps more 

 accurately by the unit structures of the chromosomes, 

 will be redistributed among the daughter and grand- 

 daughter plants in new combinations. Some of these 

 will be advantageous to the plant, and it will succeed 

 better and be able to reproduce more freely; other com- 

 binations may be less favorable, and the plants with 

 such combinations will have a poorer chance in the 

 struggle for existence, and will not reproduce so freely. 

 As a result, "Natural Selection" sorts out those whose 

 combinations are most favorable. Thus we see that 

 sexual reproduction forms a means by which the con- 

 stantly arising individual differences (and why they arise 

 we do not know) are made use of in the most manifold 

 combinations, the most favorable of which are perpet- 

 uated. This is what was called by Darwin "The 

 survival of the fittest." 



165. These inheritable variations may be slight or 



