The volume ends with four Appendices. In the first of these, Professor Poulton collects Darwin's arguments against the hypothesis of multiple origins of species. In the second, he brings together, in like manner, Darwin's utterances on evolution by mutation. In the third he returns to the aesthetic question, and proves that scientific work was necessary to Darwin's physical well-being. In the fourth he unearths a divergence of opinion, as between de Vries and certain of his followers, on the subject of the hereditary transmission of fluctuating variations. But surely the divergence is apparent only; the author has failed to distinguish between minute variation that is ancestrally determined and the fluctuation exhibited by pure lines.
This interesting and well-written essay is a reasoned plea for a practical eugenics. Civilization is in danger from the lessening of the action of natural selection; of late years, the means of keeping alive the falling and the fallen have grown with ever-increasing speed; and humanitarianism has tended towards sentimentality. At the same time, the social organism has grown self-conscious; there is a new-won appreciation of the issues at stake. Hence it is in order to inquire how far selection, natural and artificial, has been the means of developing the race, how far it is still acting and in what directions, what will be the effect of that action, and whether it can be controlled in any way to favor the preponderance of the best physical, mental and moral qualities.
If selection is to work, individuals must vary, variation must be inherited, and certain kinds of inherited variation must reproduce themselves at a quicker than average rate. We shall, therefore, in the pursuit of the inquiry outlined above, begin with the consideration of the laws of variation and of heredity. The authors give, first, a general discussion of the scientific study of these topics, illustrating them by reference to simple cases of Mendelian inheritance, of normal distribution, etc.; incidentally they show that Galton's law of ancestral inheritance may be reconciled with the Mendelian principle of particulate inheritance if, instead of a single individual, we consider large numbers: "the frequency of Mendelian dominance would produce, on the average of large numbers, greater resemblances of children to their parents than to their grandparents and to more distant ancestors."
They then treat, chiefly on the basis of Galton's work, of inheritance and variation in mankind. Special chapters are devoted to the inheritance of mental defect and ability, and to the rise and decline of families. At this point the authors turn to the third condition of the operation of selection, the necessity of reproduction, and discuss in three chapters the birth-rate, the selective birth-rate: its effects, and the decline in the birth-rate: its causes. "In the British Isles certainly, and probably in Western Europe generally, the best elements of the population are increasing, if they increase at all, at a much slower rate than the less worthy stocks, and, in some cases at any rate, the better classes are actually diminishing in number." The outcome must be deterioration, and eventually the passing of the race. Why, then, do the worthier classes desire to restrict their offspring? The authors find a number of contributory causes: the feeling of overwhelming responsibility towards children, expense, the advent in society of persons whose newly acquired wealth is not associated with definite territorial or local traditions, the cult of games, the restless-
