84 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



Significance of the descent from trees. — As a result of the descent 

 from the trees, certain definite factors were called into play, each of 

 which had its effect on the further evolution. Briefly enumerated, 

 these are: (i) Assumption of the erect posture; (2) liberation of the 

 hands from their ancient locomotor function to become organs of the 

 mind; (3) loss of the easily obtainable food of the tropical forests, 

 necessitating the search for sustenance, both plant and animal, and 

 man became a hunter; (4) need of clothing with increasing inclemency 

 of the weather, especially during the long winters; (5) freedom from 

 climatic restrictions — when an omnivorous diet and clothing were 

 acquired man was no longer limited to one definite habitat and the 

 result was dispersal; (6) the development of communal life, rendered 

 possible by the terrestrial habitat. Primates are at best gregarious, 

 submitting, as in the gorilla, to the leadership of the strongest male, 

 but it is only by communal life with its attendant division of labor 

 that man can rise above the level of utter savagery. 



Evolutionary changes. — -Human evolutionary changes which are 

 recorded are: more erect posture, shorter arms, perfection of 

 thumb opposability, reduction of muzzle and of size of teeth, loss 

 of jaw power, development of chin prominence, increase in skull 

 capacity, diminution of brow-ridges, diminution in strength of zygo- 

 matic or temporal arch, increase in size and complexity of brain, 

 especially frontal lobes, development of articulate speech. 



FOSSIL MAN 



Fossil remains of man are found under two conditions, in river 

 valley deposits and in limestone caverns which served first as a 

 dwelling-place and later as a sepulture. Of these the caverns 

 have been by far the most productive, but they contain only the 

 remains of the later races, as the caverns according to Penck did not 

 become available for human occupancy before middle Pleistocene 

 time. 



The rarity of human fossils may be explained, first, by the various 

 burial customs which seldom are sufficiently perfect to preclude the 

 possibility of alternate wetting and drying or of rapid oxidation, both 

 of which are prohibitive of fossilization. If man lived and died in the 

 forests the chances for his fossilization, in common with other forest 

 creatures, was very remote, for the remains of such are almost invari- 

 ably destroyed by other animals, by dampness, or by fungi, and rarely 

 attain a natural burial in sediment. If, on the other hand, he dwelt 



