THE OUTLOOK 
self-destruction have been evoked from time to time, 
$0 as virtually to annihilate successive, civilisations. Or 
again, it is not improbable that various kinds of diseases 
and plagues have acquired from time to time a viru- 
lence which he could not withstand. The modern 
history of epidemics indicates that their fluctuations 
are very extraordinary, and it is not unlikely that in 
prehistoric days the human being was less efficient in 
spontaneously developing protective reactions against 
a menacing environment. That he had large animals 
among his living enemies is evident from their remains; 
but the nature of his struggle with them can hardly be 
conjectured. To-day, however, they have practically 
disappeared, and the total loss from venomous rep- 
tiles, or ferocious animals, is relatively small. What 
he suffered from insects we have no idea, and it may 
be added that entomologists are by no means certain 
that in the future Man has nought to fear from his 
smaller enemies. 
Further, it is by no means impossible that there 
have been cosmic disasters of which neither historical 
accounts, nor geological nor astronomical evidences 
remain. From facts that have come to hand through 
developments in astronomy and astrophysics, leading 
to the great surveys now being made of the solar 
system and of the stellar universe, these can be readily 
visualised. The present intense activity of the solar 
surface, and the changes that are taking place thereon, 
have been studied for only a few decades. It is be. 
coming increasingly evident that climatological changes 
on the earth are largely due to physical alterations 
in the sun, and to variations in the energy radiated 
from its surface. It is likely that all manifestations of 
life are correlated with the energies received from the 
centre of our solar system, but so far we do not know 
whether Man’s actual power to increase his numbers is 
wholly dependent upon great meteorological factors 
[3