210 ADAPTATION AND PROGRESS 
provided the physiological correlate of the psychical change we 
are endeavoring to explain and we find many different anatomical 
factors championed as the most important. Darwin stresses 
erect posture and prehensile thumb; Heineman holds that the 
mutation which made erect posture possible was in the ento- 
cuneiform bone and position of the foramen magnum, and that 
this change, forcing man from the tree life of his ancestors, left 
him at so great a disadvantage in the struggle for existence that 
success was possible only by the use of the little intelligence he 
possessed to outwit his rivals, this necessity and use determining 
the whole succeeding order of his evolution;! others, on the con- 
trary, hold that the development of the intellect came first and 
led to a new mode of life in a new environment and that this fur- 
nished the occasion for physiological variations and the selection 
of those that were especially serviceable. Delay in the closing of 
the sutures of the skull was an important factor,? so too, were the 
development of the apparatus of speech, the organ of speech 
located by Broca in the third frontal convolution of the brain,? 
the nervous connection between the organ and the apparatus, the 
development of the cerebrum, and the free use of the forearms 
made possible by erect posture and terrestrial life. 
Approaching the problem from the standpoint of psychology 
we have two lines of study, the first using the comparative method 
with the endeavor to find the differential psychical element be- 
tween man and beast, and here the power of abstraction and 
association of ideas seems at present to be most stressed; and 
second, the method used by Baldwin and others, of observing the 
steps in the child’s mind by which the transition is made from 
reflexive and instinctive activity to that which is self-conscious 
and purposeful. 
From the sociological point of view we have a study of the 
materials furnished by the development of civilization as a whole, 
of separate groups and of contemporary social movements, by 
means of which we are able to analyze the social factors that 
enter into the transition. 
1 The Physical Basis of Civilization, p. 31. 
2 Keane, Ethnology, ch. III. 5 Macnamara, Human Speech, ch. X. 
