Joseph Daniel (J.D.) Unwin was a British ethnologist and social anthropologist at Oxford and Cambridge whose definitive work was the research he did with 80 primitive tribes and six known civilizations over a long period of time. The results of this research are penned in his 1934 book, Sex and Culture. What Unwin discovered was the link between cultural achievement and sexual restraint. According to Unwin, societies that practiced heterosexual monogamy were more successful societies.

Below are several quotes that flesh out Unwin’s conclusions.

“If the British anthropologist J. D. Unwin is correct in his assessment of society, this present generation in the Western world may be the last one. In his book, Sex and Culture, professor Unwin studied eighty ‘uncivilized’ cultures and compared his results with sixteen ‘civilized’ cultures extending over the last 4,000 years. He found that when strict heterosexual monogamy was practiced, the society attained its greatest cultural energy, especially in the arts, sciences and technology. But as people rebelled against the prohibitions placed upon them and demanded more sexual opportunities, there was a consequent loss of their creative energy, which resulted in the decline and eventual destruction of the civilization. Remarkably, he did not find any exception to this trend.”

—Janosik, Daniel. “The Fate of Culture in J. D. Unwin’s ‘Sex and Culture’” in Christian Apologetics Journal,
 Vol. 10:1 (Spring 2012)
.

“Unwin concluded that the fabric that holds a society together is sexual in nature. When life–long heterosexual monogamous relationship is practiced, the focus is on the nurture of the family and energy is expended to protect, plan for, and build up the individual family unit. This extends to the entire society and produces a strong society focused on preserving the strength of the family. However, he found that when sexual opportunities opened the door to pre–marital, post–marital, and homosexual relationships, the social energy always dissipated as the individual focused more on self–gratification rather than societal good.”

—Janosik, Daniel. “The Fate of Culture in J. D. Unwin’s ‘Sex and Culture’” in Christian Apologetics Journal,
 Vol. 10:1 (Spring 2012)
.

“Unwin’s conclusions, which are based upon an enormous wealth of carefully sifted evidence, may be summed up as follows. All human societies are in one or another of four cultural conditions: zoistic, manistic, deistic, rationalistic. Of these societies the zoistic displays the least amount of mental and social energy, the rationalistic the most. Investigation shows that the societies exhibiting the least amount of energy are those where pre-nuptial continence is not imposed and where the opportunities for sexual indulgence after marriage are greatest. The cultural condition of a society rises in exact proportion as it imposes pre-nuptial and post-nuptial restraints upon sexual opportunity.”

—Huxley, Aldous (1946). “Ethics” in Ends and Means, Chatto & Windus, pp. 311-12.

Now read David Fowler’s same-sex marriage commentary that also references J.D. Unwin