Byron has sung[109] of the old popular belief in the advantages of cross-breeding, which arose originally in the practice of exogamy (marriage outside the tribe), or, more often, outside those having the same totem, or coat-of-arms. In all probability casual observation of deformities after intermarriage enforced the prohibition which arose after the killing of female children had led to exogamy. Totemic relationship was often far from being consanguineous. The idea of incest is, as Byron's stanza denotes, of religious origin rather than innate.[110] Its criminal nature is often removed by priestly dispensation in Latin countries. From this practice sprang the medical, theologic, and legal notions to which D. H. Tuke[111] thus refers: "The danger arising from marriages of consanguinity has been insisted upon from time to time by medical writers, and has been recognised by ecclesiastical authority, civil law, and by popular feeling. As regards ecclesiastical and civil law, it would be more correct to say that the marriage of those very nearly related has been forbidden on other grounds than that of the alleged danger to mental health. At the same time the justice of such laws receives support if medical observation leads to the conclusion that consanguineous marriages tend to generate idiocy and insanity." The biologic evidence from the experiments of Maupas on parthenogenesis, elsewhere cited, is seemingly supported by the results of animals breeding in-and-in. The evidence advanced against such marriages seems at first sight exceedingly strong from a biologic standpoint in man. Rilliet[112] cites cases tending to show that consanguineous marriages, in themselves pernicious, tend with certainty to lower vital force. The effects he divides into two categories; those which relate to the parents, under which head are:-- _a._ Failure of conception. _b._ Retardation of conception. _c._ Imperfect conception. Those which relate to the progeny:-- _a._ Imperfections of various kinds. _b._ Monstrosities. _c._ Imperfect physical and mental organisation. _d._ Tendency to diseases of the nervous system, such as epilepsy, imbecility, idiocy, deaf-mutism, paralysis, and various cerebral affections. _e._ Tendency to strumous diseases. _f._ Tending to die young. _g._ Tendency to succumb to disease which others would easily resist. C. H. S. Davis,[113] of Meriden, Connecticut, states that intermarriages in families lead to a degeneration that manifests itself in deaf-mutism, albinism, and idiocy. Isaac Ray[114] is of the opinion that consanguineous marriages repeated through successive generations account for the numerous instances of insanity and idiocy occurring in quiet rural populations of New England, far from the excitements of city life, which are generally supposed to be more productive of mental unsoundness.