THE EVOLUTION OF LIFE 7
Ererythiiig in nature is gro^wing older and changing in eondition; slowlj or rapidly, depending npon circumstances; the meteorological elements and gravita- tion are tearing down the high places of the earth; the eroded materials are transported to the bottoms of valleys, lakes and seas; and these results beget farther consequences.
Thus, in answer to our second question, it certainly appears that living matter does not follow the old evolutionary order but represents a new assemblage of energies and new types of action, reaction, and interaction — ^to use the terms of Newton — ^between those chemical ele- ments which are as old as the cosmos itself, unless they prove to repre- sent, as Clarke, Lockyer, and Butherford have suggested, an evolution from still simpler elements.
Third, is there a continuation of the same physico-chemical laws? Yes, so far as we observe, the process is still evolutionary rather than creativBj because all these new characters and forms invariably arise out of new combinations of preexisting matter and appear to broadly conform to the laws of thermodynamics, and especially to Newton's third law. According to the interpretation by Pupin of this third law of Newton, action and reaction refer to what is going on be- tween material parts in actual contact, whereas interaction refers to what is going on between two material parts which are connected with each other by other parts. Action and reaction are simultaneous, whereas interaction refers to an action and reaction which are not simul- taneous. For example, when one pulls at a line the horse feels it a little later than the moment at which the line is pulled ; there is interaction between the hand and the horse's mouth, the line being the interconnect- ing part.
In this lecture I shall attempt to show that since in their simple forms living processes are known to be physico-chemical and are more or less clearly interpretable in terms of action, reaction and interaction, we are compelled to believe that complex forms will also prove to be interpretable in the same terms.
If we affirm that the entire trend of our observation is in the direc- tion of the physico-chemical rather than of the vitalistic hypotheses this is very far from affirming that the explanation of life is purely materialistic or that any present physico-chemical explanation is either final or satisfying to our reason. Chemists and biological chemists have very much more to discover. May there not be in the assemblage of cosmic chemical elements necessary to life, which we shall distinguish as the "life elements/^ some Jcnown element which thus far has not be- trayed itself in chemical analysis? This is not impossible, because a known element like radium, for example, might well be wrapped up in living matter but as yet undetected, owing to its suffusion or presence in excessively small quantities or to its possession of qualities that have escaped notice. Or, again, an unknown chemical element, to which the
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