192 EVOLUTION OF THE EARTH 



surrounding the Roman Empire were also suffering from 

 drought and famine. Therefore they began to make raids, 

 which set more prosperous people also into motion, and soon 

 barbarian invasions threatened the very existence of the 

 Roman Empire. If the climate had remained favorable there 

 might have been an occasional raid, but there is no reason to 

 think that there would have been the great disasters which 

 finally became so terrible. 



Worst of all, the climatic changes seem to have had a sad 

 effect upon the energy of the Romans themselves. We have 

 already seen how close is the connection between climate and 

 energy. As the variability of the Italian climate decreased 

 because the storms diminished in number, the energy of the 

 people seems also to have declined. This was particularly 

 unfortunate because special energy was needed to resist the 

 ravages of malaria, to overcome the agricultural difficulties, to 

 engender the self-control and patience which are essential when 

 political difficulties arise because of undue taxation or other 

 causes. Most of all, energy was needed to resist the invasions 

 of barbarians, but instead of this the people's energy declined. 

 They became prone to sit still and wait for someone to feed 

 them, prone to think only of pleasure, and hence ready for 

 the disaster which finally overtook the Roman Empire. 



It would be interesting to carry this discussion farther and 

 see how these same principles apply to almost every country. 

 It is easy to attribute too much to climate, and I am well aware 

 that many of my hearers will think that I have done so in this 

 lecture. It must be remembered, however, that this is merely 

 a brief attempt to show the importance of one of the great, 

 factors in the evolution of civilization. The fact that the 

 importance of climate is here emphasized does not mean that 

 I deem it a whit more important than the other factors. So 

 far as inherent mental capacity is concerned climate is in one 

 sense a minor factor. It is more important as regards material 



