268 



Supplement to '* Nature," August 1 8, 1923 



sporadically in North Africa and Central Asia. Here 

 again we see characters which were worked out in 

 fcetal months passing on to become characters of 

 adult life. 



Such examples could be multiplied to a wearisome 

 extent. I do not wish to minimise the number and 

 importance of transient simian features which appear 

 in the body of the human foetus and infant ; they are 

 well known and of great significance. But 1 do desire 



to give a true interpretation to_ such Tiu man" 



as are represented TSyT ^rTs small face and jaws; his 

 forehead, tendmg to^je devoid of supr a-(; )rhiti3l rJHgPc • 

 his large hearij[^ise(roira long and relatively slen(jgf 

 jneck : they are features firs tj^raducett" JfT tlie-Jcatal^ 

 stages ofTiigher primates and now retained by man in 

 his adult state. _Th&J endpnry -te procorvc such fo e tftl ^ 



characters is seen in certain genera of S onrp Amenra n 

 monkeys. But all "tKe~tossil progenitors of ape and-> 

 man' wejiflvp y^T <lntrr<vpf^fl ha ve a face, jaws, skull ^ 

 afid^neclTorthe more prirnitive and bestial type. 



The Bearing of Fcetal Inheritance on 

 Huxley's Conception. 



I return to Huxley's disbelief in " use-inheritance " 

 and to his conviction that animals — including man — 

 tend to evolve " along their predetermined line of 

 modification." It is clear that the mammalian 

 placenta, particularly that kind of placentation which 

 occurs in the womb of man and of anthropoids — 

 identical systems — cannot in any way be accounted 

 for by " use-inheritance." They have been worked 

 out by properties inherent in embryonic tissues. The 

 fact that the most characteristic features of the human 

 body appear first in embryonic or foetal life, and that 

 human-like characters appear transiently in fcetal 

 stages of anthropoid apes, the further fact that many 

 constant structural modifications of man's body are 

 seen as occasional variations of the ape's body, all 

 bear out Huxley's dictum that evolution tends to 

 evolve along predetermined lines of modification. 

 The machinery of evolution works out its untrammelled 

 ends in the embryo and the foetus, except in so far as 

 that machinery can be injured or deflected by what 

 may be termed poisons of the germ-plasm. It is clear, 

 too, that if we are to cast man's horoscope we can 

 read the omens only in the tendencies manifested in 

 his embryonic and fcetal stages. We can alter man's 

 future only in that limited way discovered by Darwin — 

 by applying his principle of selection. 



A Simile. 



To make my meaning clear, let me borrow a simile 

 from human affairs. Some thirty years ago, in the 

 incipient stages which led to the modern development 

 of the great motor-car industry, small workshops 

 sprang up in almost every town and supplied a car 

 of local design for local needs. The struggle for 

 survival set in, and successful types, ousting local 

 types, led to the formation of great firms which catered 

 for the needs of continents. The workmen engaged 

 and the types of car made became specialised and 

 standardised. These great firms, we know, keep an 

 eye on the market — benefit by experience — and modify 

 their types to suit demand. Invention succeeds 

 invention in their workshops. But in the factory 



where human types of body and mind are produced 

 I am presuming there is no intelligence department. 

 I am also presuming, as Huxley did, that the workmen 

 — the cells of the embryo — employed in turning out 

 new human machines, are specialised into vocational, 

 hereditary castes — each caste turning out its work i; 

 a certain way — a way which ensures a function;: 

 result. I am presuming, too, that the workmti 

 represented by the embryonic cells are co-ordinated 

 in their toil by an elaborate system of intercommunica- 

 tion — already described — the system of hormone- 

 All hands in the human factory are co-ordinated- 

 not by orders from managers or foremen, but by , 

 self-regulating system of hormone-control which work 

 out functional ends automatically. Variations — useful 

 adaptations — are produced by a bias which is inherent 

 in the machinery of control. The mere fact that I 

 have to resort to so crude a simile shows how ignorant 

 we still are of the machinery' of animal evolution. 



Conclusion. 



John Hunter gave utterance to an important truth 

 when he said man's bony and vascular tissues retained 

 the same automatic purposive behaviour as is mani- 

 fested by the lowest forms of organised life, such as 

 the hydra. In the formative period of the human 

 embryo, and on the phase when adaptational con- 

 trivances are being worked out in its heart, brain, 

 muscles, and skeleton, the embryonic cells retain many 

 of the purposive, almost conscious, attributes possessed 

 by primitive unicellular organisms. No doubt the 

 behaviour of embryonic cells, as of the simplest 

 protozoa, will prove to be reflex in nature — mere 

 protoplasmic reactions to appropriate stimuli. In 

 bringing about the collective reactions of embr^-onic 

 tissues, which mould them to form structural adapta- 

 tions, we may presume that hormones play a leading 

 role. The hormone system, to give the results it does, 

 must be framed upon a teleological basis. 



If we would rightly understand the evolution of 

 the machinery of adaptation, or, what is the same thing, 

 the machinery of government, in the developing body 

 of an animal, we shall do well, as Herbert Spencer 

 suggested, to study the evolution of a people rising 

 from savagedom to civilisation. In the earlier stages 

 of the evolution of human society we see that the 

 machinery of government is represented by the auto- 

 matic working of a herd-instinct — an instinct tending 

 in all its operations towards the preservation of the 

 community. The instinct is biassed in the direction of 

 producing functional or effective results. We have 

 to study what, in our present ignorance, we must call 

 the " herd-instincts " of the vast community of proto- 

 plasmic units embraced by the body of a human embr>-o, 

 if we would understand how the structural contrivances 

 of the human body have been evolved. I, for one. 

 believe with Huxley that the government which ruk 

 within the body of the embryo proceeds along its wa\ 

 altogether uninfluenced by occurrences or experiences 

 which affect the body or brain of the parent. In 

 short, man has come by his great gifts — his brain, his 

 upright posture, his strange foot and his nimble hand- 

 not by any effort of his own, but, like a favoured child 

 of the present day, has fallen heir to a fortune for 

 which he has never laboured. 



Printed in Great Britain *j' R. & R. Clark, Limited, Edinburgh. 



