HEREDITY. 85 
with regard to the most important things involved in the 
theory, in order to satisfy his mind that there is great 
diversity of opinion.” (Fairhurst.) 
The general abandonment of the Darwinian hypothe- 
sis by biologists, adverted to in our next chapter, is main- 
ly due to the failure of heredity to account for the gradual 
modification of organs and of habits. 
Various expedients are resorted to by Haeckel and 
a few others in their attempts to bolster up a theory which 
has broken so signally on the rock of heredity. Prin- 
cipal among these is the reference to unlimited time. 
It is asserted that, after all, such minute differences might, 
in the course of many ages, result in new and more perfect 
organs. However, here a new and unexpected difficulty 
presents itself. The physicist, who has measured the heat 
of the sun, rises up and says that the age of the earth, as 
estimated by specialists like Lord Kelvin, is not nearly so 
great as is demanded by the Darwinian. The period 
which the physicists, in their mercy, appear to be willing 
to grant the inhabitable globe is from twenty to forty 
million years. But the evolutionists maintain with great 
fervor that this period is far too short for the pro- 
duction of such complicated types of organism as now 
live on the earth; they demand from two hundred to a 
thousand million years! And so these two groups of 
scientists, the evolutionistic biologist and the physicists 
are hopelessly at odds. 
A new generation of evolutionists has within the past 
twenty years arisen which holds that the changes in the 
organizations of plants and animals do not come by slow 
growth of favorable characteristics, but arise suddenly. 
Such is the “Mutation” theory of Hugo de Vries. But 
science has failed to receive this and similar theories with 
the same acclaim which once greeted Darwin’s “Origin of 
Species.” Naturalists have become cautious. They re- 
