INTRODUCTION 7 
diversity has become what we perceive it to be, we have to confess an 
ignorance nearly total.”—William Bateson, Problems of Genetics 
(1913), p. 248. 
“The demonstration of evolution as a universal law of living 
nature is the great intellectual achievement of the nineteenth century. 
Evolution has outgrown the rank of a theory, for it has won a place 
in natural law beside Newton’s law of gravitation, and in one sense 
holds a still higher rank, because evolution is the universal master, 
while gravitation is among its many agents. Nor is the law of evolu- 
tion any longer to be associated with any single name, not even with 
that of Darwin, who was its greatest exponent. It is natural that 
evolution and Darwinism should be closely connected in many minds, 
but we must keep clear the distinction that evolution is a law, while 
Darwinism is merely one of the several ways of interpreting the work- 
ings of this law. 
“Tn contrast to the unity of opinion on the law of evolution is the 
wide diversity of opinion on the causes of evolution. In fact, the 
causes of the evolution of life are as mysterious as the law of evolution 
is certain. Some contend that we already know the chief causes of 
evolution, others contend that we know little or nothing of them. 
In this open court of conjecture, of hypothesis, of more or less heated 
controversy the names of Lamarck, of Darwin, of Weismann figure 
prominently as leaders of different schools of opinion; while there are 
others, like myself, who for various reasons belong to no school, and 
are as agnostic about Lamarckism, as they are about Darwinism or 
Weismannism, or the more recent form of Darwinism, termed Muta- 
tion by De Vries. 
“Tn truth, from the period of the earlier stages of Greek thought 
man has been eager to discover some natural cause of evolution, and 
to abandon the idea of supernatural intervention in the order of 
nature. Between the appearance of The Origin of Species, in 1859, 
and the present time there have been great waves of faith in one 
explanation and then in another: each of these waves of confidence 
has ended in disappointment, until finally we have reached a stage 
of very general scepticism. Thus the long period of evolution, experi- 
ment, and reasoning which began with the French natural philosopher, 
Buffon, one hundred and fifty years ago, ends in 1916 with the general 
feeling that our search for causes, far from being near completion, has 
only just begun. 
