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Show 120 THE DESCENT OF MAN. PART I. time, the femora to the tibiro were as 244 to 230; and in three Negroes as 258 to 241. The humerus is likewise shorter relatively to the forearm. This shortening of that part of the limb which is nearest to the body, appears to be, as suggested to me by Mr. Forbes, a case of compensation in relation with the greatly increased length of the trunk. rrhe Aymaras present some othe1~ singular points of structure, for instance, the very small projection of the heel. These men are so thoroughly acclimatised to their cold and lofty aLode, that when formerly carried down by the Spaniards to the low Eastern plains, and when now tempted down by high wages to the gold-washings, they suffer a frightful rate of mortality. Nevertheless Mr. Forbes found a few pure families which had survived during two generations ; and be observed that they still inherited their characteristic peculiarities. But it was manifest, even without measurement that these peculiarities had all decreased ; and on me~surement their bodies were found not to be so much elongat~ d as those of the men on the high plateau; whilst the~r f~~ora ha~ become somewhat lengthened, as had their t1bue but m a less degree. The actual measurements may be seen by consulting Mr. Forbes' memoir. From these valuable observations, there can, I think, be no doubt t~at residence during many generations at ~ great.elev~twn ten~s, b~th d~rectly and indirectly, to mduce mhented modrficatwns m the proportions of the body.33 ~lthough man may not have been much modified durmg the latter stages of his existence through the 33 Dr. Wilcke~s ('Lanch~irthschaft. Wochenblatt,' No. 10, 1869) ha~ lately publtshed an IUterestino- essay shewing how d t" . ammal h. h 1. · 0 omcs 1c modifie~. w lC tve m mountainous l'egions, have their framea CIIAl' lY. MANNER OF DEVELOPMENT. 121 increased or decreased use of parts, the facts now given shew 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 mfer, that when at a remote epoch the progenitors of man were in a transitional state, and were changing from quadrupeds into bipeds, natural selection would probably have been greatly aided by the inherited effects of the increased or diminished use of the different parts of the body. Arrests of Development.-Arrested development differs feom arrested growth, as parts in the former state continue to grow whilst still retaining their early condition. Various monstrosities come under this head, and some are known to be occasionally inherited, as a cleft-palate. It will suffice for our purpose to refer to the arrested brain-development of microcephalous idiots, as described in V ogt's great memoir.34 Their skulls are smaller, a~d the convolutions of the brain are less complex than m normal men. The frontal sinus, or the projection over the eye-brows, is largely developed, and the jaws are prognathous to an "e.ffrayant" degree ; so that these idiots somewhat resemble the lower types of mankind. Their intelligence 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 active, continually gamboling and jumping about, and making grimaces. They often ascend stairs on all-fours; and are curiously fond of climbing up furniture or trees. \f\T e are thus reminded of the delight 3{ ' Memo ire sur les 1\Hcroeephales,' 1867, p. 50, 1 25, 169, 171, 184- 198. |