No. 607] 



BATS AND EVOLUTION 



397 



his species, selecting from among their blue offspring 

 those which are the most like a good exhibition Wyan- 

 dotte, and so on, for a number of generations. It is easy 

 to see that in such a case the general potential variability 

 of the whole group is very much increased. It diminishes 

 automatically again, because of the fact that in every 

 generation a few animals produce a great number of off- 

 spring. If ten young cockerells of a new species of fowl 

 were habitually derived from ten fathers, the progress 

 in the direction of purification, '^fixing" the breed, would 

 be almost nothing. But as ten young males habitually 

 have only one or on the average less than one father, in 

 other words, as only a very small percentage of males 

 in every generation is used for breeding purposes, auto- 

 matic purification, automatic diminishing of the total 

 potential variability of the group, is very rapid. It is to 

 be noted that in the absence of selection, the group may 

 become pure for almost any conceivable genotype given 

 in the potential variability, the genotypic diversity of the 

 first animals. Therefore any character which has re- 

 ceived no or small attention from the breeder may turn 

 out to be different from what it was in the species to be 

 altered into a new breed. It is for this reason, very com- 

 mon to observe that a number of apparently closely re- 

 lated species in the common fowl, or in domestic pigeons, 

 differ, not only in the points which are obvious to every 

 observer, but in other minor points as well, points which 

 need not be in any way correlative to the obvious dif- 

 ferences. A few examples. The different species of Leg- 

 horn resemble each other very closely, differing to a 

 casual observer in color only. But the comb of black 

 Leghorns is noticeably larger than that in white and 

 brown Leghorns and the ears of the black species are 

 larger than in the brown and the white. The white Leg- 

 horn has a lesser tendency to become broody than the 

 buff. The hens lay more eggs than those of the buff or 

 the black breed. The plumage is generally looser and 

 longer in buff Leghorns than in blacks. 



