Pace Six 



EVOLUTION 



September, 1928 



If the land gradually sinks — the earth crust is ever 

 rising and falling — the mud and sand can accumulate 

 until an enormously thick layer is formed. The lime 

 or silica contained in the water would tend to cement 

 the particles into a solid mass, aided by the pressure 

 of the overlying sediments and by the heat resulting 

 from that pressure and derived from the earth beneath. 

 Meanwhile the animal matter will disappear and be re- 

 placed by lime or silica, thus forming a layer of rock 

 containing fossils. The very rocks themselves may con- 

 sist largely of fossils, chalk, for example, being mostly 

 the disintegrated shells of simple marine animals called 

 foraminifers. 



Even after an object has been fossilized, it is far 

 from certain that it will remain in good condition until 

 found, while the chance of being found is exceedingly 

 small. Only here and there has nature made the con- 

 tents of the rocks accessible by turning the strata on 



edge, heaving them up into cliffs or furrowing them 

 into valleys. A vast number of the pages of the fossil 

 record must ever remain unread. The wonder is that 

 we have learned so much, for nature is careless in keep- 

 ing the records — preserving only scattered fragments 

 and then subjecting them to many accidents. Some get 

 badly flattened by the weight of subsequently deposited 

 strata, others are cracked and twisted by movements -of 

 upheaval or subsidence, and if at last they are brought 

 to the surface, the same sun and rain, frost and snow, 

 from which they once escaped, are ready to renew 

 the attack and crumble even the hard stone to dust. 

 That, briefly, is why fossils are not more plentiful, why 

 we have mere hints of the existence of many animals 

 and why myriads of creatures may have flourished and 

 passed away without leaving behind so much as a trace 

 of their presence. 



Brains — How Come ? 



By All.-vn Strong Broms 



MAN heads the class in brain power because he got 

 the lucky breaks. That pre-monkey ancestor who 

 took to the trees did him a couple of good turns. For 

 one thing, he developed the skilful hands to help man's 

 brain do its stuff. We have already discussed that. Also, 

 his tree life made his eyes over into the best of all guides 

 by giving them a new power. That was a second big 

 boost. But that is really the end of this story and we 

 must begin at its beginning. 



Man's earlier ancestors smelled their way through life. 

 Some had sharp eyes, but for learning the really vital 

 things they used their noses. Smell, and its kindred 

 sense taste, told all that was important about food. 

 Smell distinguished friends from enemies, sexual mates 

 from sexual rivals. Food or poison? Friend or enemy V 

 Mate or rival? Those are vital problems of animal lilc. 

 And the animal nose knows. 



But smell tells nothing of direction, form and several 

 other details. The eyes do that. The warning sniff 

 of danger that brings a deer up alert probably comes 

 down the wind, but the deer never can tell for sure 

 until it sees. Nor does it know whether the enemy scent 

 means a h/^rmless passer-by or a stalking hunter, until 

 it sees. "Safety first" might seem to dictate, "Beat it 

 while the beating is good," but the question, "Which 



way?" makes it best to "stop, look and listen." One 

 look tells which way, tlie definite guiding fact to which 

 can be fitted a definite, and therefore eff^ective, course of 

 action. 



Exact and detailed knowledge comes, not through the 

 nose, but through the eyes. And real animal intelligence 

 arose only when the eyes supplanted the nose as the 

 m.ain gateway to the thinking brain. For millions of 

 years, however, smell held sight down, for u happe)ied 

 that there was not room enough in the brain for both, 

 nor on the face either. To understand this, we must 

 take a look at the brain. 



For present purposes, the brain of a back-boned ani- 

 mal may be divided into front-brain (top brain in 

 monkeys and man) and rear-brain, the latter in several 

 sections. The special job of the front-brain is gathering 

 new information and thinking about it. The rear-brain 

 handles nothing but old automatic routine. The front- 

 brain associates, which is just high-brow for putting two 

 and two together. It compares and chooses, — courses of 

 action, for instance. It considers new problems, decides 

 what to do about them and then orders the muscles to 

 do the work. 



The rear-brain does not think; it just acts, and always 

 in the old, routine ways. But if circumstances change, 



Bf\^lN OF Th£ Jumping 5mrew 



BRftIN Of ThE TBEE SHfltw 



MOTOR 

 PRtffiONTAL 



BfVMN OF THE TAR51EA 



ACOU5TIC 



BRAIN OF TKF MARnojET 



VH41KlIc) 



Brain development resulting from tree life. 1. Ground dwelling Jumping Shrew guided by smell (olfactory); 2. Tree Shrew guided 

 more by vision, less by smell; 3. Pre-monkey Tarsius, see* one ob'ect with both eyes, but not stereoscopically; 4. Marmoset, our low- 

 est monkey, sees stereoscopically, its large perfrontel area controlling eye convergence and muscular accord. 



From G, Elliot Smith. 



