40 THE DESCENT OF MAN. 



elevation tends, both directly and indirectly, to induce in- 

 herited modifications in the proportions of the body.* 



Although man may not have been much modified during 

 the latter stages of his existence through the increased or 

 decreased use of parts, the facts now given show that his 

 liability in this respect has not been lost ; and we positively 

 know that the same law holds good with the lower animals. 

 Consequently we may infer that when at a remote epoch 

 the progenitors of man were in a transitional state, and 

 were changing from quadrupeds into bipeds, natural selec- 

 tion would probably have been greatly aided by the in- 

 herited effects of the increased or diminished use of the dif- 

 ferent parts of the body. 



Arrests of Development. There is a difference between 

 arrested development and arrested growth, for parts in the 

 former state continue to grow while still retaining their 

 early condition. Various monstrosities come under this 

 head; and some, as a cleft-palate, are known to be occa- 

 sionally inherited. It will suffice for our purpose to refer 

 to the arrested brain-development of microcephalous idiots, 

 as described in Vogt's memoir, f Their skulls are smaller, 

 and the convolutions of the brain are less complex than in 

 normal men. The frontal sinus, or the projection over the 

 eye-brows, is largely developed, and the jaws are pro- 

 gnathous to an t( effrayant" degree; so that these idiots 

 somewhat resemble the lower types of mankind. Their in- 

 telligence, and most of their mental faculties, are extremely 

 feeble. They cannot acquire the power of speech, and are 

 wholly incapable of prolonged attention, but are much 

 given to imitation. They are strong and remarkably ac- 

 tive, continually gambolling and jumping about, and mak- 

 ing grimaces. They often ascend stairs on all-fours; and 

 are curiously fond of climbing up furniture or trees. We 

 are thus reminded of the delight shown by almost all boys 

 in climbing trees; and this again reminds us how lambs 

 and kids, originally alpine animals, delight to frisk on any 

 hillock, however small. Idiots also resemble the lower 



*Dr. Wilckens (" Landwirthschaft. Woclienblatt, " No. 10, 1869) 

 has lately published an interesting Essay showing how domestic ani- 

 mals, which live in mountainous regions, have their frames modified. 



fMernoire sur les Microcephales," 1867, pp. 50, 125, 169, 171, 

 184-198. 



