4o6 The Inward Urge to Change 



superior intelligence." And Professor Osborn finds it *' sur- 

 prising that under these circumstances the Neanderthal brain 

 attained the large dimensions which threw even the genius 

 of Huxley off the track as to the very primitive character 

 of this race." But why is this surprising? We may observe 

 the outcome of the various processes, both known and un- 

 known, at work and leading to the phenomena which we call 

 collectively ** progressive evolution," or development in 

 rather well defined directions. We may also distinguish be- 

 tween these end results and hypothetical causo-mechanical 

 factors from which result or emerge determinate variations, 

 and which we call for convenience " orthogenesis." //, now, 

 there is actually at work an agency that brings about deter- 

 minate variation or directed evolution, as Osborn believes 

 there must be, then we should not be surprised at the relatively 

 rapid evolution of the human brain and of the concomitant 

 mentality. Somewhere in the past there must have emerged 

 a situation in which was inherent the orthogenetic develop- 

 ment of man, the inevitable development of man, as Nageli 

 would say. 



We should not be surprised, furthermore, since we know 

 nothing of the circumstances that led to hypothetical 

 mutations in the direction of larger brains. Osborn, in his 

 writings, sometimes combines orthogenesis with natural 

 selection. At other times he sees orthogenesis at work 

 independent of natural selection, or even in spite of natural 

 selection. It may be, however, that orthogenesis is merely 

 a description of what the students of the facts have seen, 

 rather than an explanation of how the changes have come 

 about. 



Explanations 



It is frequently difficult to distinguish between a de- 

 scription and an explanation. What do we mean when we 

 " explain " an event or a fact? What is a " good " explana- 



