164 The Descent of Man. 



cave-men the chin is almost wanting. A recent discovery 

 of human remains of the pre-Indian period in Arizona, goes 

 to show that primitive man was deficient in speech, as these 

 skeletons retain the primitive distinction of other speech- 

 less mammalia,' in having the hyoicl bones separated. In 

 man as we now know him, these bones are consolidated, 

 forming a single bone. 



The general theory of descent rests upon the study of 

 species in detail. There can be no doubt in the mind of 

 the student that the specific lines of definition are movable. 

 Each species has stages of variability, when it is com- 

 paratively plastic, and susceptible of change, before it 

 has developed an unyielding contour and form. After- 

 wards they develop into fixed types, and do not evolve 

 into other species thereafter. This is the condition in 

 which we find most of the animal forms at the present 

 day. Our cats, for example, are not variable, or are 

 variable only within specific limits. Dogs, on the contrary, 

 are very variable, and so are barn-yard fowls. Mankind is 

 in a condition of plasticity or variability, and herein lies 

 great promise of human progress in the future. 



In attempting to account for the evolution of man, we 

 have two theories, one of Lamarck and the other of Darwin. 

 Lamarck devoted himself to explaining the origin of 

 species, but not to the special problem of natural selection. 

 The post-Darwinians, as they have been happily named by 

 Romanes, have generally accepted Darwin's hypothesis as 

 a complete explanation of evolution, but we are beginning 

 to see that Lamarck's views cannot be set aside, and that it 

 is of great importance in explaining theorem of variations. 

 Without it, natural selection would have no opportunity for 

 operation. The Darwinians say that animals and plants 

 have a tendency to variation. But nothing happens acci- 

 dentally — there can be no variation without a cause. Seek- 

 ing out these causes of variation is the province of a certain 

 school of biologists at the present time. To this study, the 

 great nations of the world are all contributing. Chemistry 

 has been called a French science. In embryology Germany 

 stands at the head. Palaeontology will doubtless constitute 

 the contribution of America to this investigation. A rich 

 field for this investigation exists in our Western States and 

 territories, rivalled only by a similar field in the Argentine 

 Republic. The fact that the earth cooled first at the poles, 



