In Sex and Culture (1934), Unwin studied 80 primitive tribes and 6 known civilizations through 5,000 years of history and claimed there was a positive correlation between the cultural achievement of a people and the sexual restraint they observe. Aldous Huxley described Sex and Culture as “a work of the highest importance”.
According to Unwin, after a nation becomes prosperous it becomes increasingly liberal with regard to sexual morality and as a result loses its cohesion, its impetus and its purpose. The effect, says the author, is irrevocable. Unwin also claimed that legal equality between women and men was a necessary prerequisite to absolute monogamy.