No doubt, disease, especially in the form of plagues and epidemics, was one of the principal causes of the slowness of increase of population throughout the Middle Ages. And this was probably non-selective as regards mental qualities, although it was strongly selective as regards power of resistance to disease, and has left the European peoples more resistant to most diseases than any other peoples, save perhaps the Chinese[124].
But many other causes of selection were at work. Disease presumably has not affected mental qualities by selection; although by direct action and mental discouragement it may have tended to the decay of civilisations; it has been argued, for example, that malaria played a great part in the decay of classical antiquity, that it was introduced some centuries B.C. and enfeebled the population of Greece and Italy.
More interesting, from our point of view of the influences affecting the mental constitution of populations, is the effect of alcohol. Dr Archdall Reid has argued very forcibly that resistance to the attraction of alcohol is a mental peculiarity which a race only acquires through long exposure to the influence of abundant alcohol; that populations are resistant just in proportion to their past exposure to it—as is true in the main of epidemic and endemic diseases—and that in both cases this is due to selection.[125]
Much careful painstaking work by continental anthropologists seems to have proved that a change of racial composition through internal selection has been and still is going on in both the German and French people. The facts have been worked out by O. Ammon[126], Hensen and De Lapouge[127]. They show, chiefly by means of the comparison of the forms of large numbers of skulls, that throughout the historic period the French and German peoples have been becoming more and more round headed, that the type of Homo Alpinus, the short dark round-headed race, has been gaining upon the type of Homo Europaeus.
We have seen that the latter stock of the fair northern type constituted the upper class among the Gauls of Caesar’s time; and the invasions of Franks and Normans must have added considerably to their numbers; yet, in spite of that, the mental and physical characters of this race are said by these authors to be now very much rarer than formerly, owing to the internal selections which have favoured the Alpine type. These took the following forms. In the first place, in the early Middle Ages, it is said, the Nordic type, being a military aristocracy, suffered, as in ancient Greece, proportionally far greater losses in warfare than the Alpine type. Secondly, the severe persecutions of Protestants in France drove into exile, besides killing many others, large numbers who were for the most part of the fair race, because, as we have seen, this race does not easily remain content within the Roman Church. It is said, for example, that, after the revocation of the Edict of Nantes, so large a number of Protestants passed into Prussia that the rise of Prussia as a powerful State was the immediate consequence, with of course an equivalent loss to France. De Lapouge considers this the greatest blow that France has suffered in the historic period. Normandy alone, it is reported, sent 200,000 Protestants to Prussia. But the most important and curious factor has been, according to De Lapouge, what he calls the selection by towns. He shows, by comparison of masses of anthropological observations, that the Nordic type has been predominantly attracted to the towns (which fact he attributes to their more restless enterprising character) while the dark type has been more content to lead the quiet agricultural life[128]. He points out that the town-life stimulates to a new struggle for adaptation, from which differentiation of classes results; the longheads maintain their numbers better and rise in the social scale. Further, he shows that town-life makes against fertility, owing to a number of psychological influences—the stimulation of ambition and of the intellect, the luxurious habits, the weakening of family life, the break with the past and its family traditions, the uncertainty of the future, the weakening of religious sanctions; and he gives reason to believe that in this way the towns have been, through many generations, weeding out the elements of the fair race and determining an ever increasing predominance of Homo Alpinus.
In order to understand the importance of these internal selections, it is necessary to realise that their effects are cumulative in a high degree, when the same influences continue to work through many generations. Thus, if within any people there are two equally numerous classes of persons of different mental constitution, A and B, and if these constitutions determine that the one group A has a net birth rate of three children per pair of adults, while the other B has a birth rate of four per pair of parents; then, in the third generation after one century, the numbers of the two classes, other things being the same for both, will be as ten to sixteen. After two centuries the one class will be more than twice as numerous as the other; and after three centuries the numbers of the class A will constitute about fifteen per cent, only of the whole population. Late marriage is also very important. Suppose that of two classes, A marries at 35, and B at 25 years, and that each produces four children per marriage; then (other things being the same) after three and a half centuries B becomes four times as numerous as A. These two factors generally work together.
But, apart from the change of racial composition of a heterogeneous nation by internal selection of this sort, changes of the constitution of even a racially homogeneous people may be produced through selection affecting persons of particular mental tendencies. One of the most striking instances of this is the elimination of the religious tendencies from the constitution of a people by negative selection through the action of the Roman Church[129]. For many centuries the Roman Church has attracted to her service very large numbers of those who were by nature most religiously minded, and it has imposed celibacy upon them, it has forbidden them to transmit their natural piety to descendants. In Protestant countries this process of negative selection of the religious tendencies was continued for a much briefer period than in the Catholic countries. It is maintained with much plausibility that we may see the result in the fact that sincere and natural piety is far commoner in the Protestant countries than in the Roman Catholic; that in the two countries Italy and Spain, in which the influence of the Roman Church has been greater than in any others, the people are now the least religiously minded of any in Europe; that with them religion has become purely formal and external, that the mass of the people, though outwardly conforming, is absolutely irreligious; that in fact this form of religion tends to exterminate itself in the long run by insisting upon that form of reproductive selection[130].
Another striking instance of the incidence of negative selection upon certain mental qualities of a people is afforded by the history of Spain. In the sixteenth century Spain attained to a supreme position of power and grandeur among the nations of the world, such as has been rivalled by Rome alone in all history; and then very rapidly her power decayed, and ever since she has remained one of the most backward of European peoples, contributing little to European culture, to science, art or philosophy, incapable of developing without the aid of foreigners her rich industrial resources, impotent in war, entirely devoid of enterprise and originality. To what is this great change due?
It is not due to any adverse change of climate, to devastation by war or plague or famine, nor is it due to any change in geographical or economic relations. Spain remains more happily situated as a centre of commerce than any other country of the world. The mass of the people remains vigorous, proud, and virile. It is the intellect of the nation alone which has decayed, or rather it is the intellectual life of the nation that has become utterly stagnant.
Buckle drew a vivid picture of the stagnation of the Spanish intellect and sought the explanation of it in the great power wielded by the Roman Catholic Church, which, he said, had successfully fostered the spirit of protection and superstition, had discouraged every effort of the intellect, and utterly repressed the spirit of inquiry, to the free activity of which all progress of civilisation was, in his opinion, due. Here, again, modern science shows that Buckle was led into error by his ignorance of the importance of the biological factors, the racial qualities and the changes produced in them by selection.