The Punishment of Incest Act 1908 (8 Edw. 7 c. 45) made it illegal for the first time in England and Wales for a man to engage in sexual intercourse with any female he knew to be his grand-daughter, daughter, sister, half-sister, or mother. Incest had until then been regarded as an ecclestiastical offence, punishable by penance. At least some feminist writers have seen this Act and others, including the Married Women’s Property Acts of 1870 and 1882, as a shift in the authority of the man as father, “private patriarchies being ‘rolled back’ by public state legislation”.
The National Society for the Prevention of Cruelty to Children and the National Vigilance Association had been campaigning for a law to criminalise incest among adults since the 1880s, on the grounds that such abuse had almost always begun before the girl had reached the age of consent. The Punishment of Incest Act was some reward for their efforts, but there was also at the time growing concern to avoid any physical and moral degeneration of the population. There had been public outcry about the poor physical condition of those enlisted for recruitment to the army during the Boer War (1899–1902), so it seems at least a possibility that step-daughters, for instance, were excluded from the list of those adults with whom it was forbidden to have sexual relations because their lack of a common genetic heritage did not pose the same dangers of in-breeding.