Chapter XV: , does enable us in the main to understand how the physical (2)

Thus in addition to the more obvious direct effects of disease upon mental and physical characters, there are the more subtle and profound effects upon temperament, and in our general summing-up we shall find reason to attribute no small importance to temperament in its influence upon progress. It thus becomes of importance to observe that in particular regions of the world certain chronic and non-lethal diseases are very common. Clearly the result of disease upon temperament is greatest when it takes the form, not of kill or cure—which is on the whole the case in temperate climates—but of chronic non-lethal maladies which are common in tropical climates, especially in Africa. The hook-worm disease is an African disease which has been introduced into America. The hook-worm (Ancylostomum duodenale) is an internal parasite which attaches itself to the lining of the intestine and causes bleeding and anaemia. Death may ensue, but the patient usually lives a long time. It is a most debilitating disease; it is said to affect some 50 per cent. of the inhabitants of some tropical and sub-tropical countries. Even as a mild infection it is the cause of much invalidity and heavy economic loss. The laziness and degeneracy of the ‘poor white trash’, who are said to belong to the purest-blooded English stock in the United States, are due not so much to the environment[1579] and heredity as to the ravages of these parasites. In a public lecture, delivered before the University of Pennsylvania, in 1915, Allan Smith, citing the factors which have caused the Southern States to lag in American progress, mentioned that the hook-worm disease ‘stands with malaria as worse than wars and the devastations of battles and worse than all other pathogenic agencies in combination’. Through the influence of these diseases ‘the men and women of the South, bred from the best colonial stock, offspring of pioneers, with the blood of English gentry and of continental cavaliers in their veins, sank lower and lower in physical degeneration and squalor, were derided and denounced as lazy and shiftless and condemned in popular opinion as worthless and a disgrace’.[1580]

There are many other tropical and sub-tropical diseases of a somewhat similar nature. Among them may be mentioned the ‘yaws’—marked by various eruptions probably due to a spirochaete—the guinea-worm, which lives buried in connective tissue; bilharzia, a trematode worm which lives in the bladder and infects nearly 50 per cent. of the inhabitants of Egypt; and elephantiasis, due to a worm related to the guinea-worm. The manner and degree in which these various diseases affect the nervous tone varies very much. In general the result is debility and a lowering of the nervous tone. So too malaria is a cause of debility, and the main reason for the decadence of Ancient Greece has been sought in this disease.[1581]

9. The results of the inquiry so far, though illuminating, are indefinite. This is largely because we are ignorant regarding innate differences. The consideration of the evidence as to identical twins offers a way out of this difficulty. It is known that there are two kinds of twins. There are the so-called identical twins, between whom there is a very close resemblance, and other twins between whom there is no greater resemblance than between any two children of the same parents. It was formerly thought that there was a sharp distinction between the two kinds of twins—identical twins arising from a single ovum, which completely separated into two halves during early development, each half giving rise to one child, ordinary twins arising from the simultaneous fertilization of two ova. If this was so, then identical twins would always have approximately the same germinal constitution, whereas other twins would have germinal constitutions as different as on the average are those of the offspring of the same parents. That identical twins do thus at times arise is practically certain, but it has recently been shown that the supposed sharp distinction between identical and other twins does not exist.[1582] This may be explained by various assumptions. It may be supposed that some ova are binucleate or that some ova are penetrated by two spermatozoa; again the earlier or later separation of the blastomeres may have a bearing upon the position. Under any of these circumstances twins intermediate between identical twins and ordinary twins would arise—twins, that is to say, not having approximately similar germinal constitutions, but germinal constitutions more nearly alike than those of ordinary twins. However this may be, it is sufficient for our purpose to note that so-called identical twins are always more alike in their germinal constitutions than are ordinary twins and may quite frequently have practically similar germinal constitutions. It, therefore, follows that differences between identical twins must be very largely of the nature of modifications. It is thus of great interest to ask in what these differences consist.

Galton collected data regarding thirty-five cases of identical twins. He summarizes the information about them up to the time at which they left the family circle as follows. ‘In a few of these not a single point of difference could be specified. In the remainder, the colour of the hair and eyes were almost always identical; the height, weight, and strength were nearly always so. Nevertheless I have a few cases of a notable difference in height, weight, and strength, although the resemblance was otherwise very near. The manner and personal address of the thirty-five pairs of twins are usually described as very similar, but are accompanied by slight differences of expression, familiar to near relatives though unperceived by strangers. The intonation of the voice when speaking is commonly the same, but it frequently happens that the twins sing in different keys.’[1583] He goes on to say that ‘both twins are apt to sicken at the same time in no less than nine out of the thirty-five cases. Either the illnesses, to which I refer, were non-contagious, or, if contagious, the twins caught them simultaneously; they did not catch them the one from the other. This implies so intimate a constitutional resemblance, that it is proper to give some quotations in evidence,’[1584] and he proceeds to give detailed evidence. Later he remarks on the ‘similarity in the association of ideas. No less than 11 out of the 35 cases testify to this. They make the same remarks on the same occasions, begin singing the same song at the same moment and so on.’[1585] With regard to tastes and dispositions Galton says that ‘in 16 cases—that is in nearly one-half of them—these were described as closely similar; in the remaining 19 they were much alike, but subject to certain named differences. These differences belonged almost wholly to such groups of qualities as these: the one was more vigorous, fearless, energetic, the other was gentle, clinging, and timid; or the one was more ardent, the other more calm and placid; or again the one was the more independent, original, and self-contained; the other the more generous, hearty, and vivacious. In short the difference was that of intensity or energy in one or other of its protean forms; it did not extend more deeply into the structures of the characters. The more vivacious might be subdued by ill health, until he assumed the character of the other; or the latter might be raised by excellent health to that of the former. The difference was in the key-note, not in the melody.’[1586] Galton sums up the evidence as follows: ‘It follows from what has been said concerning the similar dispositions of the twins, the similarity in the association of their ideas, of their special ailments, and of their illnesses generally, that the resemblances are not superficial, but extremely intimate. I have only two cases of a strong bodily resemblance being accompanied by mental diversity, and one case only of the converse kind.’[1587]

It has to be remembered that up to this period the twins had been reared under very similar conditions indeed; Galton in fact says that they had been reared ‘exactly alike’.[1588] He goes on to ask what changes were produced when they left the family and went out into the world. He sums up the result of his inquiries into this point as follows: ‘Here are 35 cases of twins who were “closely alike” in body and mind when they were young, and who have been reared exactly alike up to their early manhood and womanhood. Since then the condition of their lives has changed; what change of nurture has produced the most variation?... They (the 35 cases) showed me that in some cases the resemblance of body and mind had continued unaltered up to old age, notwithstanding very different conditions of life; they showed me that in other cases the parents ascribed such dissimilarity as there was, wholly or almost wholly to some form of illness.’[1589] ‘We may, therefore, broadly conclude that the only circumstance, within the range of those by which persons of similar conditions of life are affected, that is capable of producing a marked effect on the character of adults, is illness or some accident which causes physical infirmity.’[1590] Galton then turns to consider the details regarding twenty cases of unlike twins and he finds that in spite of similar surroundings no growing resemblance can be traced.[1591]

10. In attempting to sum up our conclusions on this subject, we may first ask what influence is to be attributed to the environment and then ask what bearing such influence has upon the main problem under review in these later chapters. It has always to be recollected that changes in the environment may have the most extreme results. Some examples were given of experiments upon developing animals, and it was shown that in the case of fish, for example, monsters of various kinds can be produced. So too doubtless extreme modifications could be produced in the case of man and are occasionally produced by untoward surroundings and by such customs as those of the distortion of the head and of the feet. What we want to know, however, is not what modifications can be produced, nor what exceptional modifications sometimes arise, but what changes are induced by the variations in the environment which usually occur.

The answer is that, putting aside disease among the factors and leaving out for the moment temperament among the characters, such variations as occur are of little importance. This applies to both physical and mental predispositions and includes the effect of not only such factors as climate and so on but also of such factors as are summed up in a good or bad home environment. It is probable that physical predispositions are on the whole more susceptible to such changes as occur than are mental predispositions. There is no reason, for instance, to think that the normal variation of any factor which influences mental predispositions produces as much effect as does use upon muscular development. But it is also further clear that, though we must, keeping aside for the moment questions connected with disease and with temperament, think of such modifications as occur as not of much importance, nevertheless these modifications are of greater importance than among species in a state of nature closely related to man. Consider for a moment muscular development. Side by side in the same street may live a man whose daily work is wholly sedentary and whose muscles are in consequence undeveloped, and a man who works in a mine or engineering shop and develops his muscles accordingly. Nowhere among vertebrate animals in a state of nature are such differences found.

Though but little is definitely known on the subject, it seems that temperament is more susceptible to changes in the environment than are other mental or physical characters. Changes of climate, for example, appear to produce more marked changes in temperament than in any other character. Temperament is certainly very susceptible to the influence of disease, which may also profoundly affect all characters both mental and physical. It is probably in its effects upon temperament that disease has its chief importance. We may even have to recognize in the effects produced by certain tropical diseases a serious hindrance to progress in tropical countries. It is difficult, however, to disentangle from the effects of disease in this sense the effects which it produces in the sense awaiting consideration in later chapters. Clearly the wide prevalence of disease, where such is the case, must form an important factor in the surroundings which the mind has for the subject-matter of its activities—but on this and on allied subjects there will be more to say later.

We have already in what has just been said referred to one kind of modification in its effect upon progress. Upon this subject in general it may in the first place again be emphasized that, so far as is at present known, there are no grounds for believing that modifications of the kind considered in this chapter give rise to mutations. From this it follows that the results of modifications are not cumulative. Unless in every successive generation the modification is induced, it will not reappear. Secondly these modifications on the whole tend, as in the case of the effect of disease upon temperament, to be connected with a condition of things that acts as a drag upon progress rather than as a spur to progress. The reason for this is clear in the light of what has been said in the last chapter. It was there shown that the germinal constitution among species in a state of nature has come to be through the action of selection of such a kind that under certain stimuli it gives rise to a certain form. This form is that which is best adapted to meet the normal features which characterize the niche in the organic world which the species occupies. Large modifications only become apparent when the species or certain members of it are no longer subject to their normal environment. To meet the new surroundings a somewhat different germinal constitution would give a better response. In other words the most satisfactory conditions are those under which considerable modifications do not arise.

Lastly we may again refer to a point that has already been alluded to. Great stress has been laid by certain authors, for instance by Professor Ridgeway, upon the influence of the environment upon man. Ridgeway in one passage speaks as follows: ‘My argument was, and is, that as the ice sheet receded, man passed upwards from the south or south-east into Europe, and settled in the three southern peninsulas, gradually spreading northwards over the Alps and extending eventually up to the Baltic. As they gradually spread upwards, under the influence of the environment (and in the environment I, of course, include food), they grew less dark, those of them who settled permanently along the axis of the Alps tending to have shorter skulls, while those who had passed upwards earliest became the most blonde and tallest people in the world.’[1592] It is clear from other passages that Ridgeway is including two very different things under the phrase—the influence of the environment. He is thinking of the production of modifications such as have been studied here, and also of the elimination of certain types under the influence of the environment. He does not make it as clear, as is perhaps desirable, to which of these two factors he attributes most importance. But what is more relevant to our argument is that to include the results of selection under the heading of the influence of the environment is somewhat misleading. Selection is a wholly different matter and, unless it is carefully distinguished from other factors, confusion of thought results. The effects which follow from elimination owing to climate and food should not be summed up under the heading of the influence of the environment; in this book they are considered in Chapters XVII and XVIII.

XVI
HEREDITY IN MAN

1. Having touched upon the influence of the environment in producing modifications, we have now to approach the subject of the selection of characters, both mental and physical. It is proposed to consider in this chapter what it is that is inherited, and in the two following chapters to consider the results of selection.

What is meant by saying that any character is inherited is clear from former chapters. There are certain predispositions in the germinal constitution of every individual—predispositions to give rise to certain characters under certain conditions and to other characters under other conditions. There is a predisposition, for instance, in the species of primrose referred to in Chapter XIV to give rise to red flowers at a certain temperature and to white flowers at a different temperature, the colour of the flower being equally inherited in both cases. We may therefore take as our starting-point the fact that there are in the constitution of every individual many such predispositions.

From the results of breeding experiments upon Mendelian lines certain conclusions have been reached which carry us farther. These experiments have shown that certain unit-characters can be isolated which behave in a certain manner when crossed, and from the manner in which they behave it is deduced that they depend upon unit-factors in the germinal constitution which are invariable. The number of unit-characters which have been detected in any one species is not large; it is true that in one species of insect about two hundred unit-factors have been found, but even this number can only form a small proportion of the total number if it is the case that the germinal constitution consists entirely of unit-factors which on crossing give the Mendelian ratio. This is the working hypothesis which is put forward as the explanation of inheritance, and which it is the object of investigators now to test. We may consider for a moment what it is that this hypothesis implies.

We have to think of the germinal constitution as containing a very large number of factors—predispositions in other words. The characters to which these factors give rise may be the characters which we see when we examine any individual, but more often they are not. There are, for instance, cases in which the colour of a flower or of the coat of a mammal are unit-characters but more often such visible characters are the product of two or more unit-factors. There are many cases now known in which the visible character is in this fashion due to the presence of several unit-factors. With regard to this hypothesis in general all that can be said is that at present no facts are known which are definitely in contradiction to it. It is the only hypothesis which holds the field.[1593]

Up to the present very few unit-factors have been distinguished in man. It has been found that brachydactyly—a peculiar malformation of the hand—presenile cataract, tylosis—a thickening of the hands and of the soles of the feet—epidermolysis bullosa—a blistering of the skin—and night blindness behave as simple Mendelian characters. So too does eye colour, pigment in front of the iris being dominant to its absence—in other words, brown, green, and hazel being dominant to pure grey and blue. There is also some reason for thinking that musical ability is a recessive character. On the hypothesis outlined above it must be supposed that most of the visible characters of man are the product of several unit-factors which have not yet been identified. What appears to happen when matings take place between people of different colour, stature, and so on is that there is a blending of characters in the offspring. Such appearances are not incompatible with the hypothesis—the assumption being that many unit-characters are concerned.

This question as to the ultimate nature of inheritance has been introduced here because of its inherent interest. It is not as a matter of fact strictly relevant. What we require to know is rather what predispositions are present in the germinal constitution. It is this which is essential; the precise manner in which the predispositions are represented in the gametes, whether by unit-factors or not, is not essential to the present inquiry. We require to be able to give some answer to such questions as whether disease, intellect, and temperament are represented in the germinal constitution or not, and we can find an answer to these questions without concerning ourselves with the ultimate nature of inheritance.

2. Since studies of inheritance on Mendelian lines do not at present enable us to say what human characters are inherited, we are dependent for our knowledge of this subject chiefly upon biometry. The method pursued by biometricians is as follows. The particulars with respect to any character—say stature—are noted both for the parents and for the children. The average degree of resemblance between parents and children can thus be measured and expressed numerically. If the resemblance was complete, if, that is to say, in respect of any character children exactly resembled their parents, the fact would be expressed by saying that the correlation was equal to unity. When the resemblance is less, the fact is expressed by representing the degree of resemblance as a fraction. It must be emphasized that this method merely measures the average degree of resemblance; it does not without further inquiry tell us how far that resemblance is due to inheritance. So far as such degrees of resemblance are found, it is quite possible, supposing that we had no further knowledge of the subject at all, that they might arise as follows. It might be that all men had the same germinal constitution, and that the degree of resemblance was due to the fact that fathers and their children were brought up under more or less similar surroundings. Though this fact should be borne in mind, such an explanation of the resemblances found in the cases that will be quoted in what follows is as a matter of fact shut out, and we may accept the correlations as a measure of the degree of likeness due to inheritance.

The correlations between parents and children and between children of the same parents have been determined in respect of many characters—both mental and physical—and found to be about 0·5. Thus, in respect of height the correlation between father and son was found to be 0·514, between father and daughter 0·510, between mother and son 0·494, between mother and daughter 0·507, between brother and brother 0·511, between sister and sister 0·537, between brother and sister 0·553. So too the average parental correlation in respect to eye colour is 0·495, and the average fraternal correlation is 0·475. With regard to ability the fraternal correlation is 0·46, the correlation between sisters 0·47, and that between brother and sister 0·44.

All that has been said with regard to the nature of fertilization and development lead to a similar conclusion. In the processes of maturation and fertilization we can detect a mechanism whereby the bearers of inherited qualities are transmitted from parent to child. In development we see how, when the appropriate stimulus plays upon the fertilized egg, an adult member of the species grows up. It is only when we suppose that within the fertilized egg there are certain predispositions in respect of every character which are derived from the parents that we can in any way understand how adult individuals come into being.[1594] And it must be emphasized that, however much opinions may differ regarding the precise nature of the mechanism of inheritance, there is no difference regarding the fact of inheritance. All biologists are agreed on this subject up to a point; the matters in debate are not strictly relevant here.

3. There are certain points, however, which, in view of the form which the discussion in the following chapters will take, require further treatment. As regards physical characters, it is sufficient to think of all such characters whether great or small as inherited. But with regard to disease it may be as well to consider further to what degree it can be said to be inherited.

What we call disease falls under two headings: disease due to the attacks of parasites and disease due to structural defects or weaknesses. Parasitic infections are of post-conceptional acquirement; they may be acquired, it is true, before birth, but such an acquirement is strictly analogous to the ‘catching’ of a disease after birth. In the sense, therefore, that parasites are not transmitted from the parent to the ovum, as the germinal constitution is transmitted, disease is never inherited.

It has been shown, however, that in the case of certain diseases, such as tuberculosis, a definite susceptibility to contract the disease is inherited. In other words, given an equal exposure to infection, some men do not ‘catch’ the disease, some only experience a mild form, and others die rapidly of it. It is probable that there are innately given degrees of susceptibility to all diseases which are caused by the invasion of the body by small, chiefly unicellular, parasites, which produce their harmful effects by the secretion of toxins. The same does not apply to the diseases caused by the attacks of the larger multicellular parasites, such as tapeworms, which, at any rate to a large extent, produce their harmful effects directly by causing lesions of the tissues. As to how far we have to think of different kinds of susceptibility to different diseases, or how far diseases go in classes, so that susceptibility to one disease goes with susceptibility to another disease and vice versa, little is known, but it is probable that in some cases at least there is a linkage of susceptibilities, that, for instance, susceptibility to scarlet fever is to some extent linked with susceptibility to measles. We must suppose that there are structural peculiarities which underlie these different susceptibilities. Though various hypotheses have been put forward, we are still ignorant as to their nature. But whatever the exact nature of these structural differences, it is clear that they are inherited like any other physical character.

We have therefore to note that (_a_) susceptibility to specific infections is inherited. If gross anomalies, such as polydactyly and syndactyly (malformations of the hand) are to be accounted as diseases, then we may note that (_b_) gross anomalies are inherited. (_c_) Minor anomalies are also inherited. Under this head come haemophilia, due to some peculiarity in the blood-vessels, which results in their not contracting as they should and to the absence of coagulating power in the blood, albuminuria, due to some defect in the filtering apparatus in the kidney, albinism, myopia, icthyosis, and others, all of which are clearly due to structural peculiarities. Further, we may note that (_d_) ‘other conditions due, it would seem, to disturbances of metabolism, underlying which may very possibly be finer anatomical variations, have for long been noted as tending to be inherited; such as obesity, diabetes, gout, and chronic rheumatism’.[1595] Lastly (_e_) certain nervous diseases are inherited. We may distinguish two classes of nervous disease—the homeomorphic and the heteromorphic. ‘In the former the offspring show the same lesions and symptoms as the parents. These are cases more particularly of lack of development or of premature atrophy of certain groups of nerve cells.’[1596] In the latter the parent may suffer from one kind of disease, while the offspring may exhibit one or more of a group of other diseases. This is attributed to a lack of development of the highest nerve-centres as a whole. There is a lack of ‘perfect stability and co-ordination of various parts so that according to the strains to which the individual members of family are subjected, now one, now the other series of centres may show itself unable to respond adequately, and one or the other form of mental disturbance and nervous disease may result. Here are to be included the condition of insanity, familial epilepsy and the neuroses.’[1597] In other words, we sometimes find stocks in which there is a nervous weakness, which may manifest itself in very various ways, including hysteria, epilepsy, inability to control impulse, delusion, and so on. Alcoholism is sometimes spoken of as though it was to be regarded as an irresistible impulse to drink. Probably we should rather imagine that a condition of general nervous weakness may at times manifest itself in the form of a loss of control with regard to the use of alcohol. According to Mott ‘there can be no doubt that neurasthenics, epileptics, imbeciles, degenerates, eccentrics, and potential lunatics—all those indeed with an inherent narrow margin of highest control—possess a marked intolerance to the effects of alcohol’.[1598] Certain facts are, however, very puzzling. Suicide, for example, would seem to be a manner in which general nervous weakness may manifest itself. Nevertheless, the tendency to suicide appears sometimes as a very definite and peculiar disease which manifests itself generation after generation at a certain age. Perhaps in these cases we should rather see an example of how the same outward circumstances—here the knowledge of the family history—tends to cause a general nervous weakness to manifest itself in the same way, rather than an example of a specific nervous weakness.[1599]

4. What we know as temperament stands half-way between physical and mental characters. As we have seen, temperament depends upon influences exerted by the functioning of the bodily organs on the nervous system and upon the peculiarities of the nervous system itself. Though on this account temperament or nervous tone is peculiarly susceptible to environmental influences, a certain condition of nervous tone is innately given. We must suppose the actual structure of the nervous system to be largely inherited, and we must suppose that the manner in which the bodily organs function is largely due to their innate organization. We have thus to think of a certain temperament as always given in the germinal constitution. An extreme example is an innate defect of the thyroid gland which can produce any degree of mental apathy. Again, such characters as excitability, rapidity of response, and differences in respect of fatiguability and recuperation are largely inherited.

Habit is best considered under this heading. The essential fact about habit is that, if the nervous system is stimulated in a certain fashion, so that a stimulus passes along certain paths, the next stimulus of the same kind will produce an impulse which passes more easily along those paths. Thus in time the same result, whatever it may be, is achieved by the application of a weaker stimulus. This fact, which is of great importance, suggests an actual modification of structure—an actual fashioning of a path. Whether this is so or not, we do not know. What is noticeable here is that the ease with which habits are formed undoubtedly differs from man to man, and we have again to postulate predispositions in the germinal constitution which tend towards a definite degree of development of the power of the formation of habits.

5. The greatest difficulties arise when dealing with the purely mental characters. There is a general agreement among biologists that mental characters are inherited just as physical characters are inherited. As we have pointed out, there is evidence to this effect derived from studies on biometric lines. The difficulties arise when we attempt to give more precision to the statement that mental characters are inherited. One method of approaching this problem is to analyse mental behaviour, and to ascertain if possible what faculties there are which cannot be explained in terms of other faculties. Such faculties are the least that we must suppose to be given in the germinal constitution. It does not, of course, follow that irreducible characters are Mendelian characters. In all probability they are due to the presence of many Mendelian factors. This analysis is a matter of great difficulty, and there is at present no agreement among psychologists as to what ultimate faculties of the mind are given out of which the characters we observe are compounded. Modern analysis leads to the idea of mental process as the activity of a subject. But though we may not think of the mind merely as a bundle of faculties, we have to attribute certain faculties to the subject, and the question arises as to what these faculties are.

There is less difficulty with regard to the affective and conative faculties, that is to say, those that are connected with feeling and striving, than with regard to the cognitive faculties. Psychologists are to some extent agreed as to what instincts can be recognized. McDougall, for instance, gives the following list, associating in each case with the impulse an emotion representing the conative or affective aspect.[1600] (1) Instinct of flight and emotion of fear. (2) Instinct of repulsion and emotion of disgust. (3) Instinct of curiosity and emotion of wonder. (4) Instinct of pugnacity and the combative emotion. (5) Instinct of self-assertion and the emotion of elation. (6) Instinct of self-abasement and the emotion of subjection. (7) Parental instinct and the tender emotion. To the remaining instincts which he names a special emotion is less definitely attached. These instincts are those of reproduction, sexual jealousy, female coyness, gregariousness, acquisition, and construction. This list is not exhaustive; there are other instincts of less importance, such as the instinct which tends to make a boy at a certain age leave his home. The list, however, includes all the more important instincts.

There are a number of other emotions often described as primary which McDougall describes as complex. Thus, according to his view admiration is a combination of wonder and self-abasement. When fear is added, we have the emotion of awe, and when gratitude is added we have the emotion of reverence. Gratitude is itself a combination of tender emotion and self-abasement. In a similar fashion loathing, fascination, and envy can be explained. According to this view, therefore, we should not think of separate predispositions towards these complex emotions as existing in the germinal constitution; we should think of them as determined by the predispositions towards the simpler emotions.

McDougall further describes three general or non-specific tendencies which have sometimes been classed as instincts.[1601] Sympathy, or the sympathetic induction of the emotions, describes the fact that instinctive behaviour incites similar behaviour in the observer. Suggestion is defined as a process of communication resulting in the acceptation with conviction of the communicated proposition in the absence of logically adequate grounds for its acceptance. Imitation, which has often been used to include sympathy and suggestion, is in the limited sense adopted by McDougall, the tendency to copy the bodily actions of some one else. Finally there is the tendency to play.

Apart, therefore, from temperament and the faculties connected with cognition, we have to recognize predispositions towards certain instincts and certain general tendencies. Without question they differ in strength from man to man; without question such differences are in large part attributable to varying predispositions in the germinal constitution, and we must presume that such differences are in some way connected with differences in nervous structure or organization. The subject is one of great difficulty, and nothing can be affirmed regarding it with any certainty. The ultimate modes of feeling seem to be those of pleasure and displeasure, and of excitement and depression. It is scarcely possible to stop at this point, and it seems that we have to go on and attribute the more specific forms of feeling or emotions to primary faculties incapable of further analysis. So, too, conation or striving seems to be distinguishable into striving towards and into striving away from an object. Again as with feeling it appears that we have to go farther and presume certain more clearly-defined faculties as indicated above.

6. The difficulties are still greater with regard to cognition. Analysis seems to bring us to three ultimate faculties—those of judgement, of comparison, and of association.[1602] Judgement consists in affirming or denying, and upon this faculty all higher reasoning is built. Memory should perhaps be considered as a special aspect of this faculty—as the power to think of an object over again, and to affirm or deny it to be the same object. This faculty, together with the faculty of comparing, enables that process of distinction and systematization to be performed upon which all the higher developments are based. To these faculties of analysis and synthesis are to be added the faculty of association, whereby objects come to be thought of in groups according to the sequence in which they came to be presented to the mind quite apart from their intrinsic affinities or distinctions. Thus, in addition to the faculties whereby the mind attains some grasp of the constitution of the world of objects, there is a faculty which in some degree mirrors the history of the world.

It is probable that in addition to these ultimate faculties, there may be many other faculties which cannot be reduced to aspects of the former, and have therefore to be considered also as primary. However that may be, what is important for our present purpose is that the faculty commonly known as ability is undoubtedly innate. It may be very variously composed of specialized forms of these three primary faculties, and perhaps of other faculties combined in very many ways. Every degree of ability is known and there are many forms in which it is specialized, such as in musical, artistic, and other directions. It has been shown that a high development of general ability is correlated with a high development of any special ability. In other words, we have to think of a genius with some marked talent as possessing on an average a high general level of ability. There is ample evidence of the inheritance of ability, both derived from the examination of large numbers of cases and from the analysis of family histories. This evidence also shows that musical and other forms of special ability are inherited. We have therefore to think of predispositions in the germinal constitution, which give rise to abilities of all kinds, although a more correct analysis may refer them to some combination of the ultimate faculties enumerated above, much as certain complex emotions are to be referred to the combination of certain primary emotions, and not thought of as given as such in the germinal constitution.

There are other characters which do not appear to be covered by any extension of the term ability. Such, for instance, are will and self-control. In its essence will seems to be the rising up of some dominating impulse which controls or harmonizes the feelings. The weaker impulse somehow overcomes the stronger. The will is variously explained, and in modern psychological writings often in such a manner as to exclude the idea of a special faculty. It is not necessary here to go into these explanations of the origin of will. It is clear that, if it has to be referred to the working of complex faculties which are themselves explicable in the terms of more ultimate faculties, it is in a sense innately given. Undoubtedly will is in a sense inherited. However much will may be a product of the environment in the second sense, there is clearly an innate tendency towards the development of a will of a certain form and strength. Whether therefore it is an ultimate faculty or not, it is due in some measure either to a definite innate predisposition or to such a combination of other innate predispositions as give rise to the manifestation of a will of a certain nature.

Finally, we may look at the whole problem of the inheritance of mental characters from another point of view. It is known that certain areas in the brain associated with particular functions are differently developed in different individuals, and that there are differences in the speed at which the nervous impulse travels which are doubtless due to anatomical peculiarities and so on—that there are, in fact, differences in the physical basis which underlies the manifestation of mental characters. It is thus easy to understand in a general way how mental characters which are based upon the nervous organization are inherited. A man may inherit a brain in which certain regions are of relatively large size, or a nervous organization by which impulses are swiftly conducted, and thus we can understand how quickness of response, power of concentration, readiness of association, type of mind (whether emotional or intellectual) are inherited.

7. This brief inquiry into what is given in the germinal constitution leads to the conception of large numbers of predispositions which under the stimulus of the environment develop into the characters that we observe. This is true at least of physical characters. In physical characters we observe the result of the play of the environment upon certain predispositions. With regard to mental characters the position is somewhat different. Into mental characters, as presented to us—into ability, for instance—there enters the influence of the environment in the second sense. When we are judging the ability of a man from a practical point of view, we are judging a character into the make-up of which has entered not only certain predispositions and a certain environment—using environment in the sense of the complement to inheritance—but also the results of the influence of the environment in the second sense, such as habit and what may be regarded as tools, namely, modes of thought and so on. In order to get at the characters we must disentangle or allow for these tools. This difficulty does not arise in the case of physical characters. When measuring the physical strength of two men we are not likely to allow one man to throw an object with a throwing-stick and another to use his own unaided strength. But we are apt when comparing ability to forget that one man may have learnt to distinguish between the categories when another may not have done so. To this difficulty we shall refer again later.

These predispositions have their basis in the germinal constitution and are therefore inherited. It is probable that we should regard the germinal constitution as consisting of unit-factors. However that may be, it is clear that either a differential birth-rate (reproductive selection) or a differential death-rate (lethal selection), will change the average germinal constitution of the race among which they are operative. Bearing this in mind, we may inquire when and where in human history we can detect reproductive and lethal selection at work. And we must remember that in the first place not merely obvious factors such as war have been and are at work, but also that subtle changes in social life and social organization may have profound effects, and that in the second place not merely obvious characters may be favoured or eliminated, but the least striking and most minute (though not necessarily the least important) characters both mental and physical may be similarly affected.

XVII
THE EVOLUTION OF PHYSICAL CHARACTERS

1. Having discussed what is given in the germinal constitution, we are now in a position to inquire into the question of changes in the germinal constitution. Such changes may affect physical or mental characters. In this chapter we are concerned with physical characters alone. Compared with the evolution of mental characters the evolution of physical characters is a subsidiary matter; as this evolution, however, has gone hand in hand with the evolution of mental characters and furthermore possesses an importance of its own, all reference to it cannot be omitted though the subject will be treated very briefly. As a preliminary to this inquiry we may note certain facts about the selection of physical characters in general.

We know practically nothing as to the cause of mutations. We have, therefore, to take mutations for granted, and to inquire how certain stocks with particular predispositions are favoured and others eliminated. In this process both lethal selection and reproductive selection play a part. Among species in a state of nature lethal selection is more important than reproductive selection; among men the importance of reproductive selection tends to increase until in the latest period it assumes an importance approaching that of lethal selection.

Hitherto we have only referred in passing to the existence of tradition among men. Tradition will be found to form a serious complication when we come to deal with the selection of mental characters. With regard to physical characters it also complicates the position, but only to a relatively unimportant degree. In the first place it makes the environment very varied, especially in industrial societies where men living next door to one another may be subject to very different conditions in their daily occupations. Secondly, the fact that men protect themselves against external conditions—for instance, against cold—may lead to a group of men who are protected surviving, where a less well-protected group perishes, though the former may conceivably be naturally less resistent to cold than the latter. In the broad and rapid survey that we shall make these complications can be disregarded; the existence of tradition does not introduce, so far as physical characters are concerned, that peculiar complication which is the cause of much difficulty when we come to deal with mental characters—namely, the combination of what is acquired through tradition with the underlying character itself in such a way that the manifestation of the character is connected in a varying degree with its innate strength. We shall thus, when dealing with mental characters, have to attempt to strip off the acquirements. When dealing with physical characters we can always get down to the character at once. There is no difficulty in separating the arm from the tool which it employs, and we thus get directly at the character which has developed as the result of the influence of certain stimuli upon a given predisposition. It is, on the other hand, difficult to separate the intellectual characters from all those traditional elements which combine with them in their outward manifestations—to measure, for example, the strength of the instinct of curiosity, which involves discounting all those elements in the tradition which may inhibit or emphasize its expression.

With regard to the strength of selection there is no exact knowledge, with the exception of some work which has been done upon statistics for modern communities. The occurrence of selection in the past is in fact merely a deduction from what we know regarding innate predispositions and regarding elimination and differential fertility. It has been shown, however, that lethal selection does occur at the present day. Professor Karl Pearson has calculated that selection accounts for a very large percentage—perhaps 60 per cent.—of the deaths at the present day,[1603] and Mr. Snow, summing up the results of an inquiry into this subject, states that ‘natural selection in the form of a selective death-rate, is strongly operative in man in the early years of life’.[1604] As it is universally agreed that, if anything, the intensity of natural selection has decreased with civilization, we may take it as certain that it was operative to as great, or to a greater, extent during the emergence of man and during what we have called the first and second periods of his history.

2. During the intermediate period, which was of relatively immense length, the greater part of human bodily evolution was accomplished. Only two or three worn and fragmentary remains have as yet been discovered from this period. It is at least apparent from them that the amount of physical evolution which has been accomplished since the end of that period is slight compared with what was accomplished within that period. We may assume that lethal selection was strongly at work. Changes in mode of life—the assumption, for instance, of a terrestrial for an arboreal existence and the adoption of an upright posture—must have involved lethal selection. These changes of habit must also have brought ancestral man into contact with new enemies. The spreading of man into new climatic zones was doubtless followed by selection, and must again have involved contact with new enemies. So, too, selection followed upon the first great steps in the acquirement of skill—the making of clothes, the use of fire, and so on. In addition to lethal selection, differential fertility acting through polygamy must have been at work. In part no doubt differential fertility merely reinforced lethal selection; but in part also it may have taken the form of sexual selection and have favoured other types.

But when we come to details we find that we are ignorant regarding the causes of even the largest changes. Some guesses have been hazarded. The increase in the capacity of the skull is connected with the evolution of the intellect and may be left for consideration in the next chapter. The decrease in the size of the jaw and the corresponding decrease in the size of the teeth were perhaps connected with a change in diet. The loss of the hairy covering may have been connected with sexual selection or it may have been favoured because it removed a lodging-place for parasites.

3. As we pass from the intermediate to the first period of human history we reach a region of less uncertainty. We are ignorant as to the physical characters of man at the close of the intermediate period, but we know that in the earlier part of the Upper Palaeolithic there was existing one variety—the Grimaldi race—which bears certain resemblances to the negroid type, and that in the latter part of the same period there were existing several varieties closely resembling types of modern European man. It seems, therefore, that, so far as this period is concerned, we have to account not merely for the evolution of the main types but also for the evolution of the less easily distinguishable varieties of man. The splitting up may have begun in the former period but it probably did not go far. As to how this evolution took place certain conclusions may first be drawn from what we know must have been the general conditions of life. Secondly, from what we know as to the position among races of the first group, rather more definite conclusions may be added concerning the nature and direction of selection.

It has already been remarked that in all probability man spread into various climatic zones before the beginning of the first period of history. The consequences of this spreading of man must have been twofold. Mankind became segregated into groups, the surroundings of which differed, first in that they were subject to different climatic environments, and secondly in that they were forced to pursue different modes of life. It is clear that, whereas in some tropical regions man would be supporting himself by hunting and collecting in such a way as to require a certain type of bodily exertion, in a temperate region he would be supporting himself by a very different form of exertion. This difference between the needs of daily life would result in the favouring of different types in the two regions. The type best adapted to gain a living in one region would be different to that best adapted to gain a living in another region.[1605]

Of far more importance in the production of varieties of men than the factors already noted are differences in climate to which man has become exposed. How great these differences are is familiar and need not be laboured. We know little with regard to the manner in which different types of man are suited to different types of climatic zones. But it is clear that in general the races of men are innately adapted to different climates. There is no historical reason why in all parts of North and South America the European races should not have ousted the American Indian as they have done in the United States. In Mexico and other regions, however, where the climate differs most markedly from that in Europe, Europeans have not succeeded in establishing themselves as they have elsewhere in the Continent. In Mexico Indian blood largely predominates over European, and the explanation must be that Europeans are not so well physically adapted to the climate as are the original inhabitants. In this there is nothing surprising. We can understand how certain types of respiratory, excretory, and circulatory organs might be better adapted than others to certain conditions of temperature, moisture, actinic rays, and so on, though we may be ignorant as to what types of circulatory and other organs are best fitted to any particular climatic zone. It would be very remarkable if it were not so, if, that is to say, any type of constitution was equally well fitted to any kind of climate. In this manner to differences in habits and in climate we may attribute the origin of the varieties of mankind.

Nevertheless, differences between races are far from being wholly due to selection on these grounds. Sexual selection is of importance. There grows up within each race a more or less clearly defined type of physical beauty, and differential fertility working through polygamy would evidently favour such types. That differences in colour to some extent represent adaptations to climate is clear; in part such differences are probably to be explained as due to varying ideals of beauty, but there are probably yet other factors entering into the evolution of racial types.