THEORIES OF LAMARCK AND DARWIN 383 
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 implics 
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 
