August 25, 192 1] 



NATURE 



809 



conquered peoples are exterminated they invariably 

 absorb or expel the conquerors. Hence the dis- 

 appearance of the Greek, Roman, Saracenic, Norman, 

 and Turkish governments. 



All, or nearly all, human microbic diseases appear 

 to have originated in the Eastern hemisphere, where 

 men first multiplied sufficiently to provide a constant 

 supply of nutriment to the parasites. Myth and his- 

 tory tell first of epidemics. Such diseases as measles 

 suddenlv appeared, attacked young and old, and then, 

 having exhausted the food supply, passed to neigh- 

 bouring populations, leaving behind a human remnant 

 which had acquired immunity. Later, when popula- 

 tions became more dense, the multitudes of new births 

 furnished a perennial supply of food, and enabled 

 many of these diseases {e.g. measles and whooping- 

 cough) to become endemic. Epidemic disease, esf)eci- 

 ally if occurring- at rare intervals, is always the more 

 terrible ; for the old as well as the young are affected, 

 and in consequence the sick are left untended, business 

 is neglected, and famine follows. Manv perish who 

 would otherwise have survived. Witness in modern 

 times the fate of many Pacific Islanders. Endemic 

 disease selects more stringently, but more cleanly ; 

 the old who have acquired immunity tend the young, 

 and only the less resistant die. Some maladies, 

 especially those which are insect-borne (e.g. malaria), 

 are confined to localities, but most others are, in vary- 

 ing degrees, "crowd " diseases. Thus in England no 

 one escapes frequent contact with measles and tuber- 

 culosis, which cause illness unless the individual be 

 immune, and death unless he be resistant. All such 

 diseases tend to become endemic as the crowd 

 thickens. We speak of the deadly climate of West 

 Africa ; but that of England is even more deadlv 

 to visitors from thinly scattered tribes {e.g. nearly all 

 savages). There is no evidence that any human race 

 is mentally unfitted for civilisation, but there is the 

 clearest evidence that, physically, only those races are 

 capable of it which have evolved in response to that 

 slowlv increasing stringency of selection which occurs 

 when populations gradually become more dense. 



Of old the sword exterminated the conquered and 

 dug deep the foundations of permanent empires. With 

 advancing civilisation and the cessation of deliberate 

 extermination, it lost its power. But when Columbus 

 ended the long separation between East and West 

 he bore weapons more deadly than the sword. Except 

 malaria he met no considerable diseases, but the 

 microbes of the East found virgin soil. Thereupon 

 commenced the greatest event and tragedy in human 

 history. The races of one half of the world began to re- 

 place those of the other half. As in the ancient Eastern 

 world, measles, small-pox, and other diseases of de- 

 finite duration swept the continent in vast epidemics. 

 They left behind them an immune remnant. But 

 tuberculosis, endemic from the first, owing to its long 

 duration in the individual, exterminated wherever the 

 conditions favoured its spread. Spain and Portugal, 

 then powerful maritime States, and first in the field, 

 elbowed the weaker British and French into the 

 seeminglv inhospitable North. But, while the tropics 

 were defended bv majaria, nothing protected the North, 

 where British and French settlers poured into the 

 vast void created bv imported diseases. The former 

 w^on the battle of Quebec. French immigration 

 ceased, and all North America fell into the grasp of 

 the Anglo-Saxon. Later the microbes created, and 

 the Anglo-Saxons are now filling, another void in 

 Australasia. Thus our race won a place in the sun, 

 and to-dav has more room for exoansion than any 

 other race. In actual truth, even if soldiers, sailors, 

 and settlers founded the British Empire, it was the 

 microbes that established it on enduring foundations. 

 NO. 2704, VOL. 107] 



I Germany began her war a century too late. If history 

 I repeats itself, the Anglo-Saxons are sure to lose their 

 I Eastern conquests, where every European settlement 

 is surrounded by a flourishing native quarter; but 

 seemingly they are rooted for ever in the West, where 

 the natives can exist only in the wilds. Every 

 travelling disease has reached almost its limits, and 

 therefore diseases, like the sword, are losing- their 

 power of founding permanent empires. The period of 

 the great human migrations is drawing to an end. 

 The story of the evolution against narcotics is 

 similar. For example, individuals differ greatly in 

 their degree of susceptibility to the charm of alcohol. 

 I Some men swiftly acquire an intense craving for deep 

 indulgence in it ; but most of us are temjjerate with- 

 out effort or very little effort. In other words, we have 

 I no great susceptibility. Speaking generally, moderate 

 drinkers are not those who resist temptation, but thoi»c 

 who are not greatly tempted. Habitual heavy drinkers 

 are always much tempted. Alcohol is a poison which 

 especially affects the habitual heavy drinker, not only 

 killing the worst cases, but also making many more 

 susceptible to numerous ills — for instance, tuber- 

 culosis. Every race {e.g. Jew, Greek, Italian, South 

 i German, South French, Spanish, Portuguese, West 

 African) which is now temperate in the presence of 

 abundant supplies of alcohol was anciently drunken. 

 That is, every race is insusceptible to the charm of 

 alcohol in proportion to the length and severity of its 

 past experience of it. Precisely the same is true of 

 opium. Natives of India take it in moderation ; the 

 Chinese in greater excess, but in less excess than 

 formerly ; while Burmans and Australian blacks in- 

 dulge immoderately and perish swiftly. Nature's un- 

 failing plan of temperance reform is to remove the 

 heavy drinker. The human plan is to remove drink 

 and leave the potential drinker to multiply. But 

 yeast and sugar cannot be eliminated, and human, 

 unlike natural, laws are sometimes disobeyed, and 

 are never immutable. 



I have tried to sketch a little of the natural 

 history of man, concerning which so little has 

 been written, but which, even politically, is so 

 much more important than his voluminously 

 described political history. The evidence, none of 

 which I think is disputable, is derived mainly from 

 medical and historical sources, but the problems which 

 arise are biological. They are too big for doctors and 

 historians, who are mere specialists. Meanwhile what 

 has biology done to establish the actuality of natural 

 selection ? She has measured some frozen sparrows, 

 she has suffocated some crabs, and she is now con- 

 ducting some "physiological experiments " to ascer- 

 tain whether "acquired" characters are "trans- 

 missible." Some of her eminent professors have de- 

 clared that natural selection is a myth, and the pulpits 

 of the contemners of science are filled with acclamations. 

 But it is mind which presents biology with the 

 greatest of her problems, tasks, and opportunities. 

 Man is the educable animal. On the mental training 

 of his young depends the intellectual status of the 

 individual and the social status of the community. 

 Men of science, especially biologists, frequently urge 

 scientific education. W^hat is it? It implies, I con- 

 ceive, the supplying of information which is likely to 

 be useful, intellectually or materially, in such a manner 

 that the pupil is left a skilful, unbiassed thinker with 

 an open, receptive, reflective habit of mind. So far as 

 possible he is taught, not what to think, but ho-w to 

 think. In the opposite type of education an endeavour 

 is made to close the mind — to bias, to stupefy, to induce 

 an artificial incapacity to profit from fresh experience, 

 to hold beliefs even in the face of conclusive evidence ; 

 in brief, to teach the pupil -whaX to think, not how 



