J. D. Unwin was a British ethnologist and social anthropologist at Oxford University and Cambridge University. Unwin wrote several books including "Sex and Culture", (1934). In "Sex and Culture" Unwin studied 80 primitive tribes and 6 known civilizations through 5,000 years of history and found a positive correlation between the cultural achievement of a people and the amount of sexual restraint which they observed. The author finds that the most culturally successful groups always exhibit lifelong monogamous relationships which include sexual abstinence outside of marriage. 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, ultimately having a negative effect on society: "The whole of human history does not contain a single instance of a group becoming civilized unless it has been absolutely monogamous, nor is there any example of a group retaining its culture after it has adopted less rigorous customs."