PRESENT PROBLEMS I.\ EVOLTTION AXI) HEREDITY. 347 



ill the sepui'iite elements of the loot aloiK', coiupletelN' neutralize eaeli 

 other so far as "-surNivar' is eoncevned : how the loot would neutralize 

 the hand, or the foot and hand wouUl neutralize the lumbar re<;ion.* 



It is this consideration of sinjile origans, the observation of their in- 

 dependent history, the rise of new eompound or«4ans by steady g'rowth 

 trom iiiiinitesimal beiiinniuiis of their sei)arate elements, the combined 

 testimony of anatomy and paheontology which force us to regard the 

 tluMiry of evolution by the natural selection of chance variations as 

 wholly untenable. With the utmost desire to regard the discussion in 

 as fair a s))irit as i)Ossible, the explanations offered by the adherents of 

 Weismann's doctrine strike me as strained, evasive, and illogical.! 



We can however by no means undervalue or dispense with natural 

 selcH-tion, which mnsr be in continuous o])eration upon every character 

 of sutticient importance to weigh in th(^ scale of survival. I need 

 hardly remind you that this selecting ]>rinciple was first discovered in 

 I81.> by Dr. W. ('. Wells, of Charleston, in connection v\ith the immu- 

 nity from certain tropical diseas(\s enjoyed by negi'oes and nuilattoes.| 



The eliminating- factor in selection is illustrated almost daily in cases 

 of appendicitis. 1 regret I have not had time to ascertain whether or 

 not this disease is considered due jjurely to accident or to congenital 

 variation in the ajjcrture of the a])pendix, which favors the admission 

 of hard objects. If so, modern surgery is only benefiting the individual 

 to the detriment of the race by its efticient preventive o])erations; and 

 (»very individual who succumbs to this disease can reflect with melan- 

 choly satisfaction that he does so pto bono publico. 



Conclusions as to the factors of <'volution. — The conclusions we 

 reach from the study of the muscular and skeletal systems are there- 

 fore as follows: 1. That in<lividual transformism in the body is the 

 main determinant of variations in the germ cells, and is therefore the 

 main cause of definite progressive oi' retrogressive variations in single 

 organs. 2. That evolution in these organs is hastened where all mem- 

 bers of the race are subject to the same individual transtbrmism. The 

 contrast between the rate of indi\'idual transformism ami ra,ce trans- 

 formism is due to the strong conservative forces of the germ ]dasina. 

 .">. That cNolution is most rapid whei'c variations are of sulhcient rank 

 to l)econn' liictors in survival. Then selection and use inheritance unite 

 forc(^s as actixc progressive })rinciples o])posing the conservative prin- 

 ci[)le in the germ plasma. 4. That fortuitous and chancer variations 

 also aris(^ from disturl)ances in the body or germ cells; they may be 

 perpetuated, or disappear in succeeding generations. 



' I Iiave expanded this idea fully in recent iiapers upon the tlieory of evolution of 

 till' horse. See ''Are Acquired Variations Inherited f" American \'atiir((}inl. Fel>- 

 ruary, ISiM. 



t See Weisinaiin's Inst essay, " Retrojijressive l)ev(do]inient.'" in .\<iliiie, IJiol. Mem., 

 trans., in press. 



I See Introduction of Darwin's ()ri(jin of Sitccies. 



