CRITIQUE OF DARWINISM 259 
Pearl; and of many mutationists who make much greater claims for 
that theory than does De Vries himself. 
Second. Each generation of biologists is so occupied with its own 
work and contemporary theories that it makes no real effort to 
understand preceding theories. 
This second tendency seems to me most marked in the attitude of 
present workers along genetic lines towards natural selection. They 
reveal an apparent lack of understanding of what Darwin really meant 
and of what he claimed; and when criticising that theory they are 
often engaged in the classic, but unprofitable, exercise of “fighting 
windmills.” 
In view of these facts I hope you will pardon me if I present in as 
few words as possible just what I believe to be the main factors which 
Darwin presented as resulting, in their actions and reactions, in 
natural selection. These factors are three in number: 
First. Heredity, by which the progeny tend to resemble their 
parents more than they do other individuals of the same species. 
Second. Individual variation, by which the progeny tend to 
depart from the parental type and sometimes from the specific type. 
Third. Geometrical ratio of increase, by which each species tends 
to produce more individuals than can survive. 
Each of these factors is practically axiomatic, so little is it open 
to argument. 
No one doubts the fact of heredity, whether pangenesis, Weis- 
mannism or Mendelism be the.correct expression of the mechanism 
involved. These do not affect the fact of heredity nor invalidate it 
as a factor in natural selection. 
No one doubts the fact of variation; whether it is the “individual 
variation” of Darwin, the “fluctuating variety” or the “mutation” 
of De Vries. All that is necessary for Darwin’s purpose is that there 
be heritable variations. That there are such things all parties agree 
and it matters little what you call them. They are adequate to act 
as a factor in the Darwinian scheme. 
No one doubts the fact of geometrical ratio of increase. It is a 
proposition easily capable of mathematical demonstration, and that 
is sufficient for Darwin’s purpose. 
These three factors, then, are not debatable as facts, whatever 
their mechanism or causes. 
A moment’s reflection will show that geometrical ratio of increase 
is a quantitative factor, giving an abundance lof individuals from 
