10 SOCIAL EVOLUTION 



species (forms of life having a certain similarity and re- 

 lated by descent) appear "all at once" by mutations. 



In support of this theory, Professor De Vries takes the 

 case of a certain evening primrose which has shown sud- 

 den and repeated leaps with a remarkable subsequent 

 constancy. The Chelidonium ma jus laciniatum ap- 

 peared suddenly in the year 1590 in the garden of an 

 apothecary at Heidelberg, and has remained constant 

 ever since. These experiments and observations have 

 lead to another theory of descent. It is now held by a 

 school of biologists represented by De Vries, that species 

 have arisen by this discontinuous process, in which each 

 new unit, forming a fresh step in the process, sharply 

 and completely separates the new form as an independ- 

 ent species from that from which it sprang. The new 

 species originates from the parent species without any 

 visible series of transitional forms. It can perhaps be 

 made more clear by figure 3. The figure represents 

 by A B the direct line of descent from which the parent 

 B has sprung. Now with the usual fluctuating or 

 continuous variation, the offspring of B would not be 

 likely to have the same average (of any trait) as their 

 own parents, but an average much nearer the average 

 of the whole group to which the parents belonged. But 

 in the case of the "sport," whose origin we are explain- 

 ing, the offspring C of B will start a new and independent 

 line of descent. That is, the offspring D of C, will not 

 have an average nearer that of B than C was, but will 

 have an average nearer that of their parents C. Thus 

 the "sport" C, has established a new group type round 

 which there will be fluctuating or continuous variation. 



Galton has illustrated the process by analogy but 

 from another point of view. The polyhedron can be 



