320 ESSENTIALS OF BIOLOGY 



years man has, very sensibly, influenced the distribution of forms 

 of Hfe on the earth ; that he has caused the appearance of many 

 new kinds of useful plants and animals, has eliminated other 

 species and that it is certain he will do so, in his own interests, 

 in an increasing degree in the future. We may place no immediate 

 limits on his power over nature. Even should human mentality 

 not evolve further than it has done, the progress of scientific 

 knowledge in the past assures us of the expectation of further 

 progress in the future. We may be certain that anything that 

 can be clearly thought out (as a train of mathematical reasoning 

 is thought out) is ultimately susceptible of " physical significance," 

 that is, may ultimately resolve itself into power over nature. We 

 may not, then, regard human evolution merely as an episode in 

 the vertebrate type of organisms, for man may become sensible 

 of whatever excess-value his own evolution implies and will 

 acquire the power of averting his own loss of dominance as an 

 animal. 



That does not mean that human civilization, as we know it, 

 may not be an episode. This civilization of the present does, 

 indeed, present no element of persistence. Clearly it expresses 

 itself in forms that are based on the exploitation of natural energy- 

 accumulations (coal and oil) that are unrenewable in those periods 

 of time by which we measure the durations of civilizations. Just 

 as clearly our present civilization will undergo extinction within 

 the few centuries, or at most thousands of years, that measure 

 the practical exhaustion of those natural energy-stores. In spite 

 of all that has become known as to the almost immeasurable 

 quantities of energy that exist in the bound mode (in the atoms) 

 w^e cannot envisage any immediate possibility of bringing that 

 energy under human control. It may be that such processes as 

 those of the " annihilation of matter " and the consequent release 

 of free energy can proceed only under conditions that make the 

 materialization of life impossible (that is in such physical states 

 as w^e imagine in the interiors of the stars) and it may be that 

 the radio-active disintegrations of the atoms are phases in the 

 passage of nature that are already " made " (Section 2e) and 

 which we cannot influence. In such a cosmic process it would 

 appear that human civilizations must revert to the persistent 

 pastoral-agricultural type. Of course what we do know of the 

 physical conditions that we call " transcendental " expresses our 



