Supplement to Nature 



No. 2807 



AUGUST 18, 1923 



The Adaptational Machinery concerned in the Evolution of Man's Body.^ 



By Prof. Sir Arthur Keith, F.R.S. 



Introductory. 



TELEOLOGY, a word so familiar to readers of 

 the works of Archdeacon Paley and of Sir 

 Charles Bell, has disappeared from the vocabulary of 

 scientific men. Darwin killed it ; he put an end to 

 natural theology and to Bridgewater treatises. Yet 

 all those wonderful contrivances which Paley culled 

 from the animal kingdom remain true ; they are facts 

 which have to be explained. The human hand is, as 

 Bell maintained, a most effectively designed structure ; ^ 

 a modern evolutionist can still study with profit the 

 account he gave of the mechanical contrivances to be 

 seen in every part of the human body.^ Modern 

 discovery has served but to heighten our sense of 

 wonder at the ingenuity which Nature has lavished on 

 the human body. The means she has installed for 

 fighting infection and internal disorders are almost 

 beyond belief. In complexity and in efficiency of 

 design the human brain far excels any invention or 

 organisation the most fertile imagination of man has 

 yet conceived. Engineers, in designing all their con- 

 trivances, ensure stability during emergencies by 

 allowing a " factor of safety " ; in all systems of the 

 human body the " factor of safety " is more than 

 ample. In this respect the human body has been 

 made almost " fool-proof." 



If, then, teleology has disappeared from our evolu- 

 tionary vocabulary, its substance remains ; we have 

 still to find a rational explanation for the manifest 

 contrivances of the human body ; a " doctrine of 

 adaptation to purpose " is still a necessity. The 

 followers of Paley had an easy task ; they had but to 

 wave a theological wand, and the origin of all of 

 Nature's contrivances was instantly explained. But 

 we followers of Charles Darwin have a much more 

 laborious undertaking in front of us ; we have to 

 discover and demonstrate in the body of man, in the 

 developing embryo, and in the growing child the 

 actual machinery which has wrought its marvellous 

 and purposive organisation. In this lecture, given in 

 memory of Huxley at his old hospital and school, I 



• The 1 2th Huxley Memorial Lecture, delivered at Charing Cross Hospital 

 Medical School on June 27. 



• The Hand, its Mechanism and Vital Endowments as evincing Design. 

 London, 1833. 



• Illustrations of Paley's "Natural Theology." An Appendix to Lord 

 Brougham's edition. 



propose to see how far modern discovery has revealed 

 the nature of the adaptational machinery of man's 

 body. 



Huxley as Human Anatomist. 



Of all the men who stood round Darwin as helpful 

 critics, Huxley has come out best ; time has upheld 

 his judgments and shown that when he doubted he 

 had the intuition of genius. His opinions concerning 

 the evolution and adaptations of the human body are 

 of particular value, for, at two periods of his career, 

 he was a close student of human anatomy. The first 

 of these was spent in this school, from 1842 to 1846, 

 when he passed from his seventeenth to his twenty- 

 first year, and quahfied for the practice of medicine. 

 Then, after sailing the high seas of zoology for a dozen 

 of years, he again made the human body one of his 

 main themes of interest, and it remained so for a period 

 of fully twelve years — from 1858 to 1871 — when he 

 again returned to the larger problems of zoology and 

 evolution. No doubt his return to the study of 

 man's body in 1858 was to correct certain doctrines 

 which Owen was promulgating concerning it, and to 

 support Darwin's " Origin of Species," which was 

 issued at the close of 1859. 



Huxley on Teleology, 



How, then, did Huxley explain the origin of those 

 excellent contrivances in the human body which had 

 commanded the admiration of so many generations of 

 anatomists ? It was not until 1876, when he was in 

 the fifty-first year of his age and at the zenith of his 

 intellectual power, that he gives us a glimpse within 

 his mind and permits us to see how he viewed teleology 

 — the science of adaptation. In the early spring of 

 1876 he gave a lecture in Glasgow, selecting " the 

 hand " as his subject — the text which had served Sir 

 Charles Bell for a Bridgewater treatise. How had 

 man come by his hand ? By what evolutionary means 

 had the clumsy climbing anthropoid hand become the 

 dexterous grasping hand of man ? If Huxley had 

 believed, as Lamarck, Spencer, and Darwin did, that 

 " functionally wrought " modifications could become 

 hereditary — that a simian stock, were it to use its arms 

 and hands as man now uses his, would in the course of 



