but individuals of a different constitution will do better as composers or 

 inventors. 



The individual differences that correspond to "constitution" are due to 

 inherited genes. A particular constitution or talent may never be trans- 

 mitted as a whole, since it results from the interaction of many genes — some 

 dominant and some recessive. Individuals will thus continue to differ from 

 their parents, but they will not deviate in a consistent direction because 

 of similar experience, as Lamarck thought. Nor will they deviate in a 

 consistent direction because of selection, as Darwin thought. The species re- 

 mains constant, just as the level of the sea remains constant, or the composi- 

 tion of the blood, on the average — that is, through constant fluctuations. 



If Species Are Constant, How Can New Forms Arise? 



Sports From time to time animal-breeders and horticulturists report 

 the appearance of an individual that is in some respect strikingly different 

 from his ancestors. Such an individual is a "sport" and it is often a deformed 

 plant or animal which cannot live very long. Or it may be strong enough to 

 survive, a freak like those exhibited in the side show of a circus. In many 

 cases, however, a sport has some valuable or interesting qualities that the 

 breeders seek to preserve. 



There appeared on a farm in Massachusetts, in 1791, a queer sheep with 

 a long body and very short, crooked legs. This freak, ancon sheep was not 

 particularly handsome. When it had grown up the owner considered the odd 

 shape of value. It kept the animal from jumping fences. By using this sport 

 as one of the parents for a new flock he obtained in the course of years an in- 

 creasing number of these short-legged sheep (see illustration below). The 

 original ancon breed was kept going about a hundred years. More recently 



There are no known descendants 

 of the original ancon ram that 

 suddenly appeared on a Massa- 

 chusetts farm in 1791. More val- 

 uable sheep sports have since 

 appeared and have become es- 

 tablished, but the ancon remains 

 of interest as a classic example 

 of a breed's becoming estab- 

 lished through the selection of a 

 recessive character that started 

 as a freak or sport. The ancon 

 mutation in the picture appeared 

 on a farm in Norway, in 1919 



I hi i^tian Wriedt 



A CLASSIC TYPE OF MUTATION 

 509 



