THE TRENDS OF EVOLUTION 179 



representative, man, they are free of the adaptive structures 

 which restrict over-all size and the size of the brain case be- 

 low critical limits. In man, size has at last been adjusted to 

 what would appear to be a happy compromise. According 

 to the fossil record, nature explored the possibility of gigan- 

 tic forms even in man but, as elsewhere, dropped back to 

 something less spectacular. The need for very rich blood to 

 nourish man's comparatively high brain requires a nicely 

 balanced, over-all physiology, and his present average size 

 would seem to be about the best. He is now unlikely to 

 evolve to any greater or smaller bulk. Eddington once 

 pointed out that man is almost precisely half-way between 

 an atom and a star in size. Our position in respect to size and 

 to other factors like food preference is very good; but be- 

 fore we indulge in our usual exaggeration and begin to con- 

 sider ourselves altogether successful, let us be reminded that 

 the check which may be working against us is our difficulty 

 in adapting to a truly cooperative and peaceful society. 



In the trend toward greater complexity we see the mar- 

 velous organizing powers of nature at work. Steadily and 

 progressively, as we have tried to show in this thesis, nature 

 has combined the basic "particles" of the substrate into pat- 

 terns of increasing intricacy-not willy-nilly, but sparingly 

 on a plan of general forms. Nature is very wasteful with in- 

 dividuals but quite conservative with form, having evolved 

 all the great variety of the world from one universal drive. 

 In Chapter 5 the basic forms of the plant and animal king- 

 doms were briefly described. They constitute, after all, a 

 wonderfully designed series with each form leading natu- 

 rally, and so logically and so economically, into those which 

 succeeded. All forms tend toward greater and greater effi- 

 ciency of organ and system function, the better to see and 

 to hear and to feel and to know. 



Out of this organizing capacity which has carried the in- 

 animate through levels from the subatomic to the atomic to 

 the molecular to the animate gene, and thence from the eel- 



