50 THE EVOLUTIONARY THEORY 



evidence was yet available that warranted an abandon- 

 ment of belief in the fixity of species. Moreover, so 

 long as men continued to believe that organic life was 

 of comparatively recent origin on this planet, the 

 amount of time which was available seemed to be quite 

 too brief for the accomphshment of a gradual evolu- 

 tion of existing species from a few protoplasmic forms 

 of life. Catastrophism, or behef in a series of vast 

 upheavals in the earth's surface, still occupied the field 

 in geological science, and this doctrine also deprived 

 the theory of a gradual evolution of species of plaus- 

 ibihty. 



The work of Sir Charles Lyell, who began to pub- 

 lish his Principles of Geology in 1830, had the effect of 

 enlarging men's conceptions of time and of overthrow- 

 ing the catastrophistic doctrine. He helped the scien- 

 tific world to beheve that all the geological changes of 

 the past have been achieved by the slow working of 

 causes that still operate, and that organic life is far 

 more ancient than had previously been acknowledged. 

 Thus he seemed to remove a difficulty which obviously 

 would have seriously hindered scientists from accept- 

 ing the Darwinian theory of evolution. The ground 

 was also broken for Darwinism by the theory of 

 Malthus, first pubhshed in 1798, but subsequently 

 elaborated.^ Malthus estabhshed the fact that human 

 population tends to increase in a geometrical ratio, 

 whereas there can be no such increase of the means of 

 subsistence. The consequence is that sooner or later 



1 Principles of Population, revised in 1803. 



