THEORIES OF LAMARCK AND DARWIN 389 



principle they will be selected, is another question and a 

 notable one. Darwin's reply was that those variations which 

 are of advantage to the individual will be the particular ones 

 selected by nature for inheritance. While Darwin implies 

 the inheritance of acquired characteristics, his theory of 

 heredity was widely different from that of Lamarck. Dar- 

 win's theory of heredity, designated the provisional theory of 

 pangenesis, has been already considered (see Chapter XIV). 



Natural Selection. Since natural selection is the main 

 feature of Darwin's doctrine, we must devote more time to 

 it. Darwin frequently complained that very few of his 

 critics took the trouble to find out what he meant by the term 

 natural selection. A few illustrations will make his meaning 

 clear. Let us first think of artificial selection as it is applied 

 by breeders of cattle, fanciers of pigeons and of other fowls, 

 etc. It is well known that by selecting particular variations 

 in animals and plants, even when the variations are slight, 

 the breeder or the horticulturalist will be able in a short 

 time to produce new races of organic forms. This artificial 

 selection on the part of man has given rise to the various 

 breeds of dogs, the 150 different kinds of pigeons, etc., all 

 of which breed true. The critical question is, Have these all 

 an individual ancestral form in nature ? Observation shows 

 that many different kinds as pigeons may be traced back 

 to a single ancestral form, and thus the doctrine of the fixity 

 of species is overthrown. 



Now, since it is demonstrated by observation that varia- 

 tions occur, if there be a selective principle at work in 

 nature, effects similar to those caused by artificial selec- 

 tion will be produced. The selection by nature of the forms 

 fittest to survive is what Darwin meant by natural selection. 

 We can never understand the application, however, unless 

 we take into account the fact that while animals tend to 

 multiply in geometrical progression, as a matter of fact the 



