Chapter XV: , does enable us in the main to understand how the physical (1)

evolution of man has come about. With regard to mental characters to be discussed in Chapter XVIII, we shall find that the task cannot be similarly completed. With a far less degree of certainty than in the case of physical characters we shall arrive at some idea as to how mental characters have evolved. This, however, still leaves unanswered the problem as to how far the evolution of mental characters accounts for what we call history. To attack this problem it is necessary to consider how the environment acts as a stimulus upon the mind, conditions the degree to which and the direction in which the mind is used, and thus leads to the building up of tradition. In Chapter XIX we consider the nature of human mental endowment and the manner in which tradition is built up and handed on. In Chapter XX we consider the nature of the environment under which human mental activities have been exerted. This will enable us in Chapter XXI to survey the broad facts of history and to come to some conclusion as to the parts played respectively by the changes in human mental endowment, by the direct influence of the environment upon the mental faculties, and by its influence as a stimulus upon the exercise of these faculties. In a concluding chapter the results of the whole inquiry will be summed up.

XIV
THE INFLUENCE OF THE ENVIRONMENT AMONG ANIMALS AND PLANTS

1. A brief inquiry into the part played by the environment among animals and plants forms a necessary introduction to a similar inquiry as regards man such as we shall undertake in the next chapter.

In the second chapter something was said as to fertilization and as to the development of the zygote or fertilized egg to the adult form. It has been shown by Herbst that, if this process of development is to result in a normal adult, all the factors comprising the normal environment must be present. Herbst ascertained the exact composition of sea-water at Naples.[1529] Using as his material the larvae of sea-urchins, he changed slightly in many different ways the composition of the water. The experiments were very exhaustive. At every stage in the development he observed the results of abstracting one or more of the constituents of sea-water—the normal environment of the larvae. Commenting upon the results of these experiments, Jenkinson says: ‘Whatever may be the ultimate explanation of the facts, there can be no doubt whatever that the most complete demonstration has been given of the absolute necessity of many of the elements occurring in ordinary sea-water, its normal environment, for the proper growth and differentiation of the larva of the sea-urchin. Nor is this all. Some of the substances are necessary for one part or phase of development, some for another, some at the very beginning, others only later on. Thus potassium, magnesium and some degree of alkalinity are essential for fertilization, chlorine and sodium for segmentation, calcium for the adequate cohesion of the blastomeres, potassium, calcium and the hydroxyl-ion for securing the internal osmotic pressure necessary for growth, while without the sulph-ion and magnesium the due differentiation of the alimentary tract and the proper formation of the skeleton cannot occur; the secretion of the skeleton depends on the presence of some sulphate and alkalinity, the skeleton requires calcium carbonate, cilia will only beat in an alkaline medium containing potassium and magnesium, and muscle will only contract when potassium and calcium are there.’[1530]

Summing up the results of these and other experiments, Jenkinson says: ‘Every factor, or nearly every factor [of the environment], is necessary for this or that phase or part of the process, some for the whole. Light of a certain wave length will accelerate development; light of another kind, or, in some instances, darkness, will retard it, or will stop it altogether; a certain degree of heat is indispensable; oxygen is required for respiration, water for growth; some eggs demand constant agitation, others complete rest; fertilization or segmentation or gastrulation, or some one or other of the later phases of development may depend absolutely on the presence of some particular chemical element; remove the factor in question, whatever it may be, and that particular process will not occur, and the specific typical end which is reached in normal development will not be attained.’[1531]

Putting aside until later the question as to what is implied by the term normal environment, we may now ask what the relation is between heredity and environment. To regard a developing organism as subject to the action of two forces, one tending to thrust it in one direction and the other in another, is to view the matter in a wholly false light. Heredity and environment are, as is clear from the evidence given above, complementary one to the other; without a germinal constitution there can be no organism; without appropriate stimuli an organism cannot develop. Similarly it is misleading to speak of the relative importance of the two factors unless the terms are very clearly defined. To see that careful definition is necessary, we have only to remember that, because, with the exception of the anaerobic bacteria, all organisms require free oxygen, environment might be held to be all important. Here, however, we are not concerned with the problem as to the conditions under which we might speak of the relative importance of the two factors; we have merely to note that they are essentially complementary.

2. We may now observe that, just as a normal adult only develops under normal stimuli, abnormal stimuli experimentally induced may be followed by every kind of result from the most extreme to the most insignificant changes both of form and of life-cycle. We may note the results of a few of the vast number of experiments which have been made. With regard to plants it has been shown that ‘each developmental stage depends upon special external conditions, and in cases where our knowledge is sufficient, a particular stage may be obtained at will. In the Green Algae, as in the case of the Fungi, we may classify the stages of development into purely vegetative growth (growth, cell-division, branching), asexual reproduction (formation of zöospores, conidia), and sexual process (formation of male and female sexual organs). By modifying the external conditions, it is possible to induce algae or fungi ... to grow continuously for several years, or, in the course of a few days, to die after an enormous production of asexual or sexual cells. In some instances even an almost complete stoppage of growth may be caused, reproductive cells scarcely being formed before the organism is again compelled to resort to reproduction. Then again the sequence of different stages of development may be modified as we desire.’[1532]

Another kind of experiment shows that foliage shoots can be converted into runners and vice versa; it is, for instance, possible to induce a germinating tuber of the potato to form foliage shoots under the influence of a higher temperature. The transfer of plants from one environment to another is often followed by remarkable changes. MacLeod, for instance, states that a species of Philodendron which has large leaves pierced with round holes was cultivated for many years in the Botanical Gardens at Ghent in a greenhouse which was rather cool and dry. The holes were found to be rare; at times it was not possible to observe a single perforation in any of the leaves of a specimen. In every other respect the plants were healthy. The plants were later transferred to a greenhouse that was warm and moist and after a few months the new leaves were found to be abundantly perforated.[1533] Bonnier made some very interesting observations on the dandelion. He found that the plant, when sown at a high altitude in the Pyrenees, produced very short stems with hairy, dark green leaves and a compact flower. On the other hand, seeds gathered from such plants growing at a high altitude and sown in the neighbourhood of Paris produced after three years elongated stems with less hairy and brighter leaves, or, in other words, plants very similar to those grown from seeds obtained in the neighbourhood of Paris. The modifications acquired during a given time by a lowland plant grown at a high altitude, or by a highland plant grown at a low altitude, took about the same time to disappear on returning the plants to their original climates.[1534] Similarly ‘Schubeler sowed seeds of various plants in different latitudes in Norway and proved that the brilliancy of the flowers increased with the latitude. So great was the difference that it was difficult to conceive that they were produced from the same batch of seeds.’[1535] Observations on European peach-trees transported to Réunion were made by Bordage. Such trees lost their deciduous habit and became evergreen, though in some cases it took twenty years before the change was complete.[1536] Lastly the red primrose ‘reared at a temperature of 30°–35° C. (with moisture and shade) has pure white flowers, but the same plants reared at 15°–20° C. have red flowers. If the white-bearing plants are brought into a cooler place, the flowers that are already in bloom remain white, but those that develop later in the cooler temperature are red.’[1537]

We may also notice the results of some of the experiments upon developing animals. Stockard experimented with the fish _Fundulus heteroclitus_. He subjected the eggs both before cleavage began, and after the two- and four-celled stages had been reached, to solutions of magnesium salts in sea-water. The eyes of a large percentage of the embryos were abnormal. In some cases there was a single median eye; in other cases there was a median eye showing signs of a double structure.[1538] ‘In a long series of experiments Féré has shown that monstrosities can be produced by exposing the hen’s egg to the unfavourable influence of a large variety of substances. Vapour of ether, alcohol, essential oils, nicotine, mercury and phosphorus, injection of alkaloids such as morphine, nicotine, strychnine and others, of bacterial toxins (those of tubercle and diphtheria), of peptone, dextrose, and glycerine, several alcohols, certain salts ... are all harmful, retarding and distorting the embryo to a greater or less extent.’[1539] Many experiments show the effect of differences in food, temperature, and humidity upon developing organisms. Agar carried out some experiments on a small water-flea, Simocephalus. This animal is enclosed in a kind of shell composed of two valves, somewhat like a mussel. Normally the edges of the valves nearly meet, so that if a section is cut across the animal transversely the shape of the body enclosed in the valves is oval. When the food was varied in a certain way, Agar found that the edges of the valves were turned outwards so that the shape of a transverse section was no longer oval but bell-like. He also found that the length was reduced by exposure to a high temperature.[1540] Experimenting with a beetle, Tower found that both the colour and the colour pattern could be modified by changes in temperature and humidity.[1541] Similarly Morgan showed that a species of the fruit fly exhibited a peculiar formation of the abdomen in the presence of moisture; when raised in dry conditions the abnormality disappeared.[1542] Poulton obtained some remarkable results when working with the larvae of moths. ‘Larvae surrounded by the leaves on which they fed, became, in the majority of species, light brown or light grey in colour. If, however, an abundance of twigs had been mixed with the leaves of the food plant, they became dark in colour. The larvae of the Peppered Moth afforded the most striking result of all, for when reared among green leaves and shoots they became bright green without exception, whilst in the presence of dark brown twigs they nearly all assumed a corresponding colour.’[1543]

A Japanese experimenter exercised rats for 90 to 180 days; he found that this long-continued exercise markedly increased the weight of the heart, kidneys, and other organs on an average to about 20 per cent.[1544] A thickening has been observed in the stomach of a gull fed on grain for a year and this change is said to take place under natural conditions in the herring gull, which feeds in winter on fish and in summer on grain. Conversely if graminivorous birds are fed on a carnivorous diet, the gizzard assumes the form of a carnivorous bird’s stomach. Cuvier found the length of the intestine of the wild boar is as 9 to 1 and of the domestic boar as 13·5 to 1, a difference which is in part probably due to diet.[1545] The colour of birds’ plumage is affected by their diet. Hempseed causes bullfinches and other birds to become black. Cayenne pepper causes yellow to change to orange red. In the New York Zoological Gardens it has been shown that some birds, such as the bobolink, may be so dieted that they keep their breeding plumage throughout the year and will sing their spring song in mid-winter.[1546] Warren produced marked changes in the common water-flea, Daphnia, by keeping them in a confined space for many generations. ‘Semper and de Varigny found that when fresh-water snails were reared in vessels of a shape that allowed them abundant water but very little surface in which to take exercise they developed into dwarf forms. Every precaution was taken to procure abundant food, perfect aeration and thorough removal of waste products. De Varigny’s experiments were particularly careful and point convincingly to the conclusion that the condition of dwarfing was the restricted area for exercise.’[1547] Lastly it may be remembered that, as is well known, parasites may induce remarkable changes in their hosts.

3. From what was said in the third chapter it follows that the results of artificial subjection to abnormal stimuli just described are to be interpreted as examples of the fact that different responses are given to different stimuli by the same or approximately the same germinal constitution. But large and conspicuous changes of this nature are not visible only as the result of artificial circumstances. Many species are normally subject to more or less definite and sudden changes in the surroundings, and some of them exhibit more or less definite responses to such changes. This is especially obvious in the case of sessile organisms the outward form of which is clearly modified by the surroundings. Thus ‘the water ranunculus, when growing submerged beneath the surface of a pond, produces leaves the blades of which are cut up into a number of fine thread-like segments. As soon as the top of the plant reaches the surface of the water, those leaf-rudiments which are just commencing their existence, proceed to develop in a totally different fashion. The leaves to which they give rise possess a wide and unpointed blade, which floats upon the surface of the water. The two sets of leaves are as utterly different in their appearance as it is possible for leaves to be. Yet the effect of the external conditions upon the young leaf-rudiment determines which of the kinds is to appear.’[1548]

Examples may also be found in the life-history of free-living organisms. One is afforded by the common honey-bee. As is well known, a queen bee differs markedly from a worker bee in shape. Both queens and workers arise from fertilized eggs; whether a queen or a worker develops from any one egg appears to depend wholly on the environment—a larva that gives rise to a queen receiving in the first place different and presumably more nutritious food than that received by a larva giving rise to a worker, and, in the second place, inhabiting a cell which differs in size and shape from that inhabited by a worker larva. Another is afforded by the life-history of the plant lice (Aphids). At certain seasons of the year winged forms appear. It has long been suspected that the appearance of winged forms depends on some environmental stimulus. That this is so has been rendered practically certain by the work of Shinji, who has shown that aphids reared on plants watered with certain solutions are winged almost without exception.[1549]

Among mammals the assumption of a winter coat by the lemming, ptarmigan, and variable hare is a similar phenomenon. Sir John Ross has told how a Hudson Bay lemming was protected from the cold on board his ship by keeping it in the cabin. It retained its normal summer coat during the winter. On exposing it in a cage on deck to a temperature of 30° below zero, the fur on the cheeks and a patch on each shoulder became perfectly white during the first night. After another day’s exposure ‘the patches on each shoulder had extended considerably, and the posterior part of the body and the flanks had turned a dirty white.... At the end of a week it was entirely white except in a dark band across the shoulders prolonged posteriorly down the middle of the back.’[1550]

A curious example of the importance of the environment before birth is afforded by the difference between the mule and the jennet. The former is the product of a cross between a stallion and a she-ass, the latter between a jackass and a mare. There is every reason to believe that it is not the fact that horse-ancestry is in one case traced through the father and in the other case through the mother that gives rise to the difference; the difference can only be attributed to the fact that in one case the period before birth is passed within a mother of one species and in the other case is passed within a mother of another species.

4. We are now in a position to discuss what is meant by the term ‘normal environment’. There is a more or less definite range of variations of the environmental stimuli to which species in a state of nature are subject. The range may differ greatly from species to species, but remains more or less constant for any species. So long as the variations fall within this range, the environment may be described as normal. Such variations will be followed by different responses on the part of similar germinal constitutions, and the variations among the members of any species under a normal environment are due to the combined influence of differences in the environment and of differences in the germinal constitutions. From time to time in a state of nature organisms are subject to variations of the environmental stimuli which fall outside the normal range, and there are thus produced extreme modifications similar to those which can be experimentally induced. Thus Gemmill on examining a large number of fish embryos found monsters with a single eye very similar to those experimentally produced by Stockard.[1551]

It may next be observed that there is a marked difference in the degree to which sessile organisms on the one hand and free-living organisms on the other hand respond to differences in the normal environment. The former are much more susceptible to differences—or at least to certain differences. Sessile organisms, for instance, differ from one another very greatly in form and such variations are known to be chiefly due to differences in the environmental stimuli. Free-living organisms do not vary in this manner. The reason is fairly clear. All species are adapted to a particular niche in nature, and among the former the mode of adaptation of necessity takes the form of susceptibility to surrounding conditions; a tree or a sponge must be able to adapt itself to its actual surroundings. A free-living organism is, on the other hand, adapted by its specific form to its niche in nature and, in order that it may reach and maintain this form, it must exhibit a relative lack of susceptibility to surrounding conditions.

5. The broad features of the situation among species in a state of nature are now fairly clear. By outward inspection it cannot be ascertained whether any particular characteristic is of the nature of a modification or of a mutation. But we know that among sessile organisms outward form is largely of the nature of modification, whereas among free-living organisms, which interest us more closely because conditions are more nearly comparable to those obtaining among men, modifications play a much smaller part. A large number of measurements has been made of certain features of particular species in a state of nature as, for instance, by Allen for the squirrel and Weldon for the common shrimp. Though on general grounds we may have reason to suspect how far the variations recorded are of the nature of modifications, we can arrive at no certain answer. Observations made on members of a species in a state of nature, some of which are subject to conditions that differ from those to which the rest of the members are subject, are of more assistance for our present purpose. Thus the tiger ranges from tropical to temperate regions. Tigers from the former regions exhibit certain differences from those from the latter regions in respect of the condition of the coat. It is possible that these differences are purely environmental. Again certain marine molluscs from cold waters exhibit differences when compared with members of the same species from warmer waters; these differences may again be purely environmental. In those cases in which a species has within recent years spread to a new environment, it is often found the degree of variation has increased. Thus Bumpus found that the egg of the common sparrow is more variable in the United States than in England;[1552] it has also been noticed that the variation of the common periwinkle is greater in America than in England—both these species having been recently introduced into America.[1553] It is also of interest to observe that Montgomery found greater variations among migratory than among non-migratory species of birds and the greatest variation among those that had the widest range.[1554] Though, until the matter has been put to the test of experiment, nothing can be affirmed as to the nature of these differences, it is probable that in part at least these differences are environmental. Such observations help to exhibit the degree of importance that we are led to attribute to modifications among free-living animals in a state of nature. It must also be borne in mind that departures from the normal range of variations of the environmental stimuli are not so very infrequent and that more or less extreme modifications, as result, for instance, from the attacks of parasites, do occur.

Lastly we may go a step farther and ask what happens when the environment changes. This inquiry, if pursued, would lead us beyond the scope of this chapter. A reference, however, to this problem may assist to render the relation of a species under natural conditions to its environment rather more clear. Change of environment may be due either to the migration of some or all the members of a species to a locality where the environment is different, or to an actual change in the environment in the same locality. If the change is at all marked, then there will be a different response on the part of the germinal constitution to the new conditions. Let us suppose that the diet is changed and that some members of a species of bird take to a diet of grain having previously existed on a diet of fish. There will be a different response in that the stomach will assume a different form. But it is most unlikely that the old germinal constitution will be that which gives the best response to the new conditions. Almost certainly a somewhat different type of germinal constitution will be that which will give the best response to the new conditions, will be that, in other words, from which there will arise the form of stomach most suited to dealing with grain. If and when, therefore, a mutation arises exhibiting this changed type of germinal constitution, it will be favoured, and in this manner a new variety and ultimately a new species may be formed. It has thus to be remembered that, although the germinal constitution to some extent responds differently to different stimuli, it is very unlikely that any average type of germinal constitution will give the best response to any other environment than that to which the species is now subject. It does not therefore follow that, because the responses of the germinal constitution are various, there are not factors making for a change in the germinal constitution when the environment changes.

Summing up what we have said, we have to think of every species as living under a more or less clearly defined environment into which very many elements enter; whether the variations in these elements are great or small, there is an average condition, and to that average condition a certain type of germinal constitution gives the best response. In the case of a free-living animal in the adult form the germinal constitution does not respond readily to ordinary variations from the normal, though it has to be remembered that extreme influences such as those caused by parasites may cause marked reactions. Further, it has always to be borne in mind that during development all animals and plants are particularly susceptible to environmental changes. It is not possible to make any precise statement as to how far the differences we see under natural conditions are modifications and how far mutations. All that we can say is that the part played by the environment in producing modifications is on the whole smaller in the case of free-living animals than in the case of sessile animals and of plants.

XV
THE INFLUENCE OF THE ENVIRONMENT UPON MAN

1. The way has now been cleared for a consideration of the influence of the environment upon man. The relation of the ancestors of man to the environment must have been the same as that between any wild species and its environment. In the course of his history man has moved away from this position until his relation to the environment has become so different from that described for other animals and plants that we can no longer speak of a normal environment. This has not come about because man is not subject to the same laws as are other organisms. It has come about because his relation to the environment has been modified in many ways.

The conception of the normal environment involved the idea that, much as the different elements composing the environment might vary, there was some more or less clearly defined limit to their variations. In one sense this remains true for man; but the variations are so much greater in degree and in kind that there is a clear distinction between the conditions obtaining among civilized races and those obtaining among any wild species. Let us glance for a moment at what has happened. It is obvious that man has varied his surroundings in every respect, not only with regard to what we may call external circumstances, but also with regard to nutrition and to customs and habits that we sum up under the name of use. The most obvious changes in external circumstances are those connected with the spread of man to every corner of every continent. Man has become subject to every extreme of heat and cold, humidity and aridity, of barometric pressure and all that goes to make up climate. There is in addition a vast mass of artificial influences, due in the first place to various methods of protection adopted against climate. Every description of house is known, involving all degrees of access to fresh air. Dress again varies almost infinitely—the variations all being of possible influence upon the development of mental and physical characters. The aggregation of men into towns involves exposure to smoke, noise, and vibration among other factors. Modern industrial conditions in particular expose workers to varied surroundings. Human diet has become equally varied. The cooking of food was an innovation involving great changes in the factors which play upon the digestive organs. Innumerable animals and plants have been drawn upon by man as food. Perhaps more important than the variations in what man eats are the variations in what he drinks. Under the heading of use come all those habits such as reading, washing, smoking, and shaving. Various occupations bring with them various degrees of muscular activity or involve its reduction to next to nothing. There are various modes of riding and various ways of sitting. Lastly the prevalence of disease has introduced another factor which has a profound influence upon mental and physical characters.

This varying of the environment has come about gradually, slowly at first and with increasing speed latterly, until at the present day, of four men having their homes in the same town one may do clerical work involving no exercise, another may labour in a cotton mill where it is warm and moist, a third may perform hard physical labour in a mine in semi-darkness where the air is full of a particular kind of dust, and a fourth may work on board ship exposed to all the rigours of the Atlantic. To such differences may be added all the differences between meat-eaters and vegetarians, smokers and non-smokers, alcoholic drinkers and abstainers, and so on. Contrast the variations in the environment of modern man with the variations in the environment of any species in a state of nature and it will be apparent why it was said above that the relation of man to his environment was clearly distinguishable from that of any species in a state of nature to its environment.

We are about to consider in this chapter the influence of the environment upon the physical basis of life; we shall be concerned, in other words, with its function as the complement of the germinal constitution. The discussion will be limited to the notice of such factors as are in operation; of the possible effects of the environment there is no need to speak. From two other points of view also the environment is of importance; as a factor in selection it will be considered in Chapters XVII and XVIII; as the subject-matter, so to speak, upon which mental processes work, it will be considered in Chapters XIX and XX. It is important to distinguish the influence of the environment in this latter respect from the sense in which it is considered in this chapter. The failure to do so has vitiated many contributions to the subject. It is felt that the environment is somehow of great influence in social life and it is not realized that, if in the respect in which it is considered in this chapter we find reason to conclude that its influence is not great, there is another field in which its influence may be established.

When considering the influence of the environment on man, it is convenient to distinguish between physical and mental characters. Mental characters may be considered under the head of the intellect, the disposition, and the temperament. It must, however, be clearly understood that this is merely a distinction convenient for our present purpose which is not based upon, and does not imply, any fundamental distinction. Mental characters, such as the instinct of gregariousness, and physical characters, such as head form, are for our purpose merely characters resulting from the play of certain stimuli upon a certain germinal constitution.

2. It is remarkable how little on the whole is known with regard to the influence of the environment on man. For the most part we have to depend upon observations as distinguished from experiments. Though a few experiments have been made, some deliberately but others accidentally, we are for the most part in the position with regard to man that we should be with regard to other animals, had we only such observations to go on as those quoted respecting the size of marine molluscs, the variation in the coat of the tiger, and the changes in the sparrow and the periwinkle when introduced into America. Though such observations may strongly suggest certain conclusions as to the part played by the environment, no definite or precise results can be reached.

We may first consider some evidence bearing upon the influence of particular factors such as exercise and climate. We may disregard those rare cases of extreme modifications deliberately induced, such as the distortion of the shape of the head or of the feet by pressure. These extreme modifications approximate to mutilations such as amputation of the finger-joints or the knocking out of the incisor teeth.

It is well known that exercise has considerable effect upon the development of the muscles. It is also well known that there is a clearly defined point for each individual beyond which exercise will produce no further effect. Though exercise has a considerable effect upon other organs, especially certain internal organs, it is probable, not only that it has more effect upon the muscles than upon any other system of organs, but that the effect upon the muscles is relatively at least as great as, if not greater than, the effect upon any organ of any other factor that we shall consider except disease. Owing to differences in the amount of exercise the bodily development of man in a modern community varies very considerably; owing to such modifications clerical workers differ from blacksmiths, whether or not there are also germinal differences. So too owing to differences in habits men of one race differ from men of another race. Darwin, for instance, refers to the thin legs and thick arms of the Payagua Indians who spend a large part of their lives in canoes.[1555] It is certain that all such physical differences are not due to germinal differences and that environment in the shape of use is in part the cause. The position is similar with regard to certain peculiarities observable among races that have adopted unusual modes of squatting.

Little is known as to the effects of use upon mental characters. To some degree no doubt the intellect is developed by use, though, perhaps, the degree to which this is so is apt to be exaggerated in popular estimation owing to the fact that modes of thinking acquired through education add to the efficiency of the faculty, which result is mistaken for the effects of use. That the effects of exercise are not great is shown by the experience of the Workers’ Education Association. This institution gives advanced courses to men often of middle age who have received but little intellectual training in early life. It does not appear that the strength of their intellects is much less than it would have been had they received a university training. It seems at any rate certain that the differences in the amount of use now obtaining between the various professions and classes in England have less effect generally upon mental than upon physical characters. Given, for example, two men of equal intellect, one of whom received the best educational training of the day, and the other of whom received the training given to the working classes, it does not seem that at the end of the training there would be anything like the same difference as regards strength of intellect between them as there would be between two men, one of whom received an athletic training and the other of whom did not.

3. Physical changes are not infrequently observed to follow upon changes in the environment, though, when these changes are complex, it is often impossible to say with which features of the environment the changes are connected. Thus ‘the Anthropological Committee of the British Association long ago showed the beneficent effects of the Factory Acts, which rescued young children from the hardships of daily toil. Boys of nine years in 1873 had a height and weight equivalent to the height and weight of boys of ten years old in 1833.’[1556]

It is known that stature has increased in certain European countries during the last century. Soren Hansen gives the following figures for Denmark:[1557]

1852 to 1856 165·42 cm. average height.
1879 „ 1888 167·78 „ „ „
1891 „ 1900 168·43 „ „ „
1904 „ 1905 169·11 „ „ „

Similarly the stature of the Dutch has increased from 165·5 cm. in 1866 to 167 cm. in 1883 and to 168 cm. in 1899. A number of reasons has been suggested to account for this marked increase, the higher standard of living, the decrease in the incidence of disease which is known to inhibit growth, and the smaller number of children in a family. This last factor is certainly of importance at the present day. From some observations made in an English manufacturing town Ewart concludes that when children are born at a longer interval than two years they are on an average three inches taller and three pounds heavier than children born at a shorter interval.[1558] It is a fair assumption that in families, where the income is small, the fewer the children the more favourable would be the environmental conditions.

The physical inferiority of people living in poorly endowed surroundings is often thought to be at least in part due to modifications induced by hard conditions. Thus physical inferiority is noticeable in districts in Europe that are markedly poorly endowed, as for instance in the area between Limoges and Périgueux in France. So far as this is so, the causes may have to be sought in climatic differences as well as in other differences more directly comparable with those which exist between well- and ill-treated children in the same country.

4. The influence of climate upon man has long attracted attention. Statistical evidence has been produced showing that the shape of the head—a characteristic usually considered not to be in any way susceptible to such differences in the environment as occur between one climate and another—is modified by climate. Boas produced figures showing that the cephalic index (a measure obtained by calculating the relation of breadth of the head to the length which is put at 100) of Sicilians born in America to be 80, while that of Sicilians born in Sicily is 78, and of Hebrews born in America to be 81, while that of Hebrews born in Eastern Europe, whence the immigrants came, is 83. It would appear that the Hebrews who are broad-headed in Europe become narrower-headed in America, and that the Sicilians who are narrow-headed in Europe become broader-headed in America. There would thus seem to be an approximation in America to a cephalic index the mean of which lies between 80 and 81.[1559] These results have been severely criticized from many points of view. Sergi claims to have shown that the results are the ‘pure effect of illusion due to the statistical methods employed by the author’.[1560] It has also been suggested that the results are due to selection. In this connexion it is interesting to note that both Ammon and Levi obtained somewhat similar results and that they both attributed them to selection. The former, working with figures from Baden, found that the inhabitants of cities tended to become longer-headed and concluded that the short-headed type tended to die out under the conditions of city life.[1561] Levi, working on Italian figures, came to the same conclusion and attributed it to the same cause.[1562] Others have suggested that the methods of nursing children may affect the shape of the head and that the changed habits of the immigrants in America may account for the changes in the shape of the head. Though it has certainly not been proved that the environment can in the manner suggested change the shape of the head, the question cannot be regarded as settled.

Observations have been made on the cephalic index of Jews which may perhaps be held to lend support to the views of Boas. Huntington gives the following table:[1563]

_Country._ _Cephalic Index of _Cephalic Index of _Difference_ Jews._ other Races._ Caucasus 87·5 87·4 0·1 Galicia 83·6 84·4 0·8 Baden 83·5 84·1 0·6 Little Russia 82·9 83·2 0·3 Turin 82·4 84·9 2·5 Lithuania 81·7 80·6 1·1 Russian Poland 81·9 80·9 1·0 White Russia 80·9 82·5 1·6

It would appear that there is a tendency for the cephalic index of Jews to vary as does that of the surrounding types. Fishberg has attributed this fact to intermarriage[1564] and this may be in part at least the explanation, though in the present state of our knowledge the possible influence of the environment cannot be altogether excluded.

The uncertainty surrounding the matter is in fact a good example of the state of our knowledge regarding many similar problems affecting man.[1565] Boas himself, it may be noticed, only believes in a ‘strictly limited plasticity’[1566] of head form; it is indeed evident that this and other physical characters which distinguish the races of man are for the most part of the nature of mutations and not of modifications. Europeans who migrate to tropical climates and the inhabitants of tropical climates who come to live in Europe retain the greater part of their distinguishing physical characters.

The manner and degree in which tropical climates influence Europeans is a matter of considerable interest. There is as yet but little known on the subject. Sir Patrick Manson, writing in 1907, said that ‘although many attempts have been made to trace and explain the effect of temperature on the physiological processes of the human body, more especially in reference to the pathological proclivities to which atmospheric heat and cold may conduce, it cannot be said that any important conclusions have been attained.... But though we may not be able to indicate precisely the way in which our bodies are physiologically affected by extremes of atmospheric temperature, especially prolonged high temperature, our sensations, the loss of physical and mental energy, the modification of physical characteristics undergone by white races when placed for several generations in tropical conditions, and the dark skins of all tropical races indicate that the white races on first arrival are not in all respects adapted for tropical conditions, that they are somehow prejudicially affected thereby, and that while living in tropical countries they are more open to certain pathological risks than are the natives of those countries.’[1567] Since the year in which Sir Patrick Manson wrote further information has been obtained on this subject. Our knowledge is, however, still scanty. With regard to actual facts it is known that the pulse, rate of breathing, and temperature of the body do not vary when measured in Europe and when measured among white men under tropical conditions. The number of red blood-corpuscles and the amount of haemoglobin in the blood is the same and metabolism is not less intense. On the other hand the rate by which a nervous impulse travels along a nerve decreases in Europeans the longer they live in the tropics. The muscles and the connective tissue become more elastic. The well-known pallor of Europeans living in the tropics is due to a thickening and softening of the epidermis, which becomes opaque.[1568]

It is very difficult to arrive at any conclusions as to what the effects of a tropical climate upon Europeans really are. It is necessary to discount the effect of tropical diseases and of the habits and customs of Europeans living in the tropics. On the whole it is probable that the popular notion of the considerable and generally injurious nature of the modifications undergone by Europeans living in the tropics is exaggerated. It is said that, for example, in Java, when sanitary conditions are good and reasonable habits adopted, the death-rate among European children is less than in Europe. Nevertheless a tropical climate does have an injurious effect upon Europeans. There is no doubt that Europeans in the tropics are more irritable and in general more highly strung than in their native land. Clearly in some fashion the nervous tone is injuriously affected by residence in tropical climates. In a similar manner nervous tone is affected by many elements in the environment in civilized countries, such as vibration, noise, and so on, leaving aside the effect of food, drink, and disease. To the importance of disease in this respect we shall return later. As regards noise, vibration, and so on, but little is known—their influence being possibly considerably greater than is usually suspected.

5. Ellsworth Huntingdon has in recent years in a number of publications elaborated a theory according to which climate has been one of the main factors in determining where civilization shall develop and flourish. As this theory depends upon the supposed direct influence of the environment on man, it may be noticed here. He has made observations which are interpreted as showing that there are optimum climatic conditions under which the maximum energy is exhibited. These conditions arise when the average temperature of day and night together lies between 58° F. and 71° F. and when there is a certain degree of moisture. His observations, made in America, were based on the output in piece-work factories and on similar data and tend to show that not only do all European races, including the Finns, display most energy under these optimum conditions, but also the Japanese and the negroes. He then proceeds to show that where these optimum conditions prevail in the world, there to-day are to be found the highest forms of civilization. Upon these data he raises a very far-reaching theory to the effect that throughout history civilization has arisen and flourished only where there has been an approximation to these climatic conditions. To the obvious difficulty that former civilizations have often flourished in countries the climate of which at the present day is far from these optimum conditions, he replies that climate has changed, a theory which he has for some years strongly advocated.[1569]

It may be said that there is nothing novel in the idea of optimum climatic conditions.[1570] In the previous section it was pointed out that Europeans in tropical climates suffer from injurious mental disturbances. What is remarkable is that the optimum conditions for negroes should be the same as for Europeans. It will require more proof than has yet been advanced before this can be accepted. Further, the changes in climate which the theory demands have not been proved. Professor Gregory has reviewed the question and his conclusions do not support those of Huntingdon—at any rate not in such a manner as to render the theory tenable.[1571] Nevertheless, whatever the fate of the theory in its present form may be, its enunciation has raised many interesting questions and has incidentally helped to show how little we know at present regarding the effect of the surroundings on man.

6. When men move from one climate to another they come under the influence not only of changes in temperature and moisture but also of food and sometimes of altitude and other factors about the effects of which there is a considerable amount of information. A vegetarian diet is said to produce changes in the gut; but changes in beverages are probably of far greater importance than changes in food. The effects of alcohol have been closely studied, chiefly with regard to its influence upon nervous tone. Nervous tone is affected in an important manner by many drugs, as for instance by opium, and in a lesser degree by tea and coffee. Changes in nervous tone are of such importance that its susceptibility to various influences has to be borne in mind. It is quite possible that the introduction of a new form of beverage into a country might have a perceptible effect upon the average condition of nervous tone and thus have a bearing upon the course of history.

Altitude is known to have various effects upon physical characters. The fact that the larger lung capacity of those who live at high altitudes diminishes on descent to the plains, as recorded by Darwin of the Quicha Indians, is evidence that this character is in part at least environmental.[1572] The effect of high altitudes has lately been studied in much detail. It is known that there is among other changes an increase in the number of red blood-corpuscles in the blood.[1573]

7. Attempts have been made to obtain more precise information by the use of statistical methods. Thus the correlations have been measured between the state of children’s eyesight and fifteen environmental conditions. The mean of the correlations was found to be 0·04—only one reaching 0·1.[1574] Again the association between various intellectual and physical characters and conditions, which were taken as representing a good or bad environment, has been measured. A slight association was found between intelligence in boys and few people per room and no association between eyesight, condition of glands and hearing, and bad economic and moral surroundings.[1575] Somewhat different results have been reached by American workers, who find that by employing psychological tests a fairly well-marked difference can be detected between children in the same school whose parents belong to different social classes and who would therefore be subject to different home conditions.[1576]

The interpretation of these results is difficult. Before any definite conclusion could be reached with regard to any one character, it would be necessary to measure the effect of every factor in the environment upon that character. As the matter stands there is strong but not conclusive evidence of the small influence of the surroundings, so long as we suppose that innate differences do not exist between the subjects measured. But if innate differences exist, then the interpretation of the absence of any marked degree of correlation must be that the common elements of the environment supplied by the community are of greater importance than the innate differences. We shall find reason to conclude in later chapters that small innate differences do exist, and, if this is so, then the interpretation of these results is not at variance with the general, though necessarily vague, conclusions derived from the evidence previously given, i.e. that the influence of the environment as represented by the variations actually occurring in the elements of the surroundings hitherto mentioned is small.

8. There is another class of factors which may be summed up under the heading of disease. It was remarked that disease may produce notable results among species in a state of nature. Compared, however, with the state of things among men, and especially in the later stages of history, disease is rare among such species. Among men it comes to assume a peculiar importance.

Disease results both from the attacks of parasites and from other causes. The various classes of disease will be referred to in the next chapter. We are here concerned only with the results, and we may think of the disease as affecting particular organs in the body and as affecting the general functioning of the organs. Every organ in the body is liable to be attacked by disease and the modifications produced are in many cases familiar. Thus all physical and mental characters may be directly and to almost any degree modified by disease. Again it is known that the result of disease in children is to inhibit growth, and that the growth thus lost is not subsequently made up. Disease may thus be said to draw upon the capital and not upon the income of children.[1577] We may here confine ourselves to some notice of the effect of disease on the general functioning of the bodily organs which though not so familiar is more important from our point of view.

The functioning of the bodily organs has been found in late years largely to depend upon certain glands—known as the endocrinous or ductless glands—in a manner and to a degree altogether unsuspected. The thyroid gland, for example, manufactures a secretion which is essential to the proper growth and normal metabolic functions of the whole body. If it is removed from a child, the whole body is stunted and mental deficiency results. Certain maladies, such as goitre, cretinism, and others are known to be connected with a diseased condition of the thyroid. Profound modifications of both physical and mental characters may thus follow when these glands cease to function normally, which is known to be the case in certain specific diseases and may arise in other ways which are not fully understood.

Temperament depends upon the general functioning of the bodily organs and upon the actual condition of the nervous system. Disease, whether it takes the form of a failure of the ductless glands to function as they should, or some other form, always affects the general functioning of the body and thus has a direct bearing upon temperament. Thus ‘we know now’, says Mr. McDougall, ‘that defect of the functions of this organ (thyroid) may reduce any one of us to a state of mental apathy bordering upon idiocy, and that its excessive activity produces the opposite effect and may throw the mind into an over-excitable condition verging upon maniacal excitement. Again we know that certain diseases tend to produce specific changes of temperament, that phthisis often gives it a bright and hopeful turn, diabetes a dissatisfied and cantankerous turn. It is clear that in some such cases of profound alteration of temperament by bodily disorder the effects are produced by means of the chemical products of metabolism, which, being thrown out of the diseased tissues into the blood and reaching the nervous system by way of the blood-stream, chemically modify its processes. It is probable that every organ in the body exerts in this way some influence upon our mental life, and that temperament is in large measure the balance or resultant of all these many contributory influences.’[1578]