the same type of sport has again appeared in this country and in Sweden, This 

 "turnspit" type of animal is sometimes found among dogs, the Dachshund 

 being a common example. 



At other times there have appeared sheep with unusually long wool, and 

 these were saved as a basis for further breeding. Peacock fanciers sometimes 

 find a single bird with plain black plumage. Several times whole flocks of 

 such birds have been established from a smgle freak mated with the normal 

 type. These sports, or jumps, occur also in plants, A wild dewberry without 

 thorns was the basis for Luther Burbank's thornless blackberry. A grain stalk 

 may appear without the sharp bristles, or awns, among the grains, A seedless 

 plum or a seedless orange grows unexpectedly upon a tree that had previously 

 borne only respectable fruit with seeds. 



Mutations^ Darwin knew of such sports, but looked upon them as 

 freaks rather than as significant features in the formation of species. In more 

 recent years biologists have been giving special attention to sports. From the 

 fact that such freak individuals sometimes establish distinct lines of descend- 

 ants, the Dutch botanist Hugo de Vries developed a theory to account for 

 the origin of new species. De Vries himself cultivated many lines of new 

 plants which originated in this sudden or discontinuous manner from evening 

 primroses and from other species, both wild and cultivated (see illustration 

 opposite). Such suddenly arising departures from the parental type de Vries 

 called mutations. The individuals bearing the new characters for the first 

 time are called mutants — from a Latin word meaning "to change". 



In most cases, the observed mutants do not deviate greatly from their 

 parents. The changes are usually confined to one or a few details, such as 

 shape or coloration or size or the number of like parts. Nor are most of the 

 mutations observed of any great importance, either as natural advantage to 

 the organism or as useful in practical cultivation. 



The mutation theory does not attempt to explain how it is that plants and 

 animals do depart from the parent types. It declares merely that new types 

 become established only if individuals appear with distinctive qualities which 

 they, in turn, transmit to their offspring. It does not assume that mutants 

 have any superiority or advantage over the parental type, although some may 

 have. It is sufficient for the theory if new types of individuals are capable of 

 living and of establishing themselves through their progeny. This theory, like 

 the theory of Lamarck and the theory of Darwin (see pages 464 and 466), 

 depends upon the facts of heredity. 



We know definitely that such jumps occur. We do not know what brings 

 about such freak behavior during the reproduction of plants and animals. We 

 know merely that such a jump away from the ancestral line is, in effect, the 

 beginning of a new species. 



^See page 522. 

 510 



