[11] Thus Heron finds that in London during the past fifty years there has been 100 per cent increase in the intensity of the relation between low social birth and high birth-rate, and that the high birth-rate of the lower social classes is not fully compensated by their high death-rate (D. Heron, "On the Relation of Fertility in Man to Social Status," _Drapers' Company Research Memoirs_, No. I, 1906). As, however, Newsholme and Stevenson point out (_Journal Royal Statistical Society_, April, 1906, p. 74), the net addition to the population made by the best social classes is at so very slightly lower a rate than that made by the poorest class that, even if we consent to let the question rest on this ground, there is still no urgent need for the wailings of Cassandra. [12] _Sociological Papers_ of the Sociological Society, 1904, p. 35. [13] There is a certain profit in studying one's own ancestry. It has been somewhat astonishing to me to find how very slight are the social oscillations traceable in a middle-class family and the families it intermarries with through several centuries. A professional family tends to form a caste marrying within that caste. An ambitious member of the family may marry a baronet's daughter, and another, less pretentious, a village tradesman's daughter; but the general level is maintained without rising or falling. Occasionally, it happens that the ambitious and energetic son of a prosperous master-craftsman becomes a professional man, marries into the professional caste, and founds a professional family; such a family seems to flourish for some three generations, and then suddenly fails and dies out in the male line, while the vigour of the female line is not impaired. [14] The new social adjustment of a family, it is probable, is always difficult, and if the change is sudden or extreme, the new environment may rapidly prove fatal to the family. Lorenz (_Lehrbuch der Genealogie_, p. 135) has shown that when a peasant family reaches an upper social class it dies out in a few generations. [15] See, on this point, Reibmayr, _Entwicklungsgeschichte des Talentes und Genies_, Vol. I, ch. VII. [16] Fahlbeck, _op. cit._, p. 168.