A new book Sex at Dawn by Christopher Ryan and Cacilda Jethá explores the ever controversial idea that marriage is an unnatural state and that there is too much emphasis on monogamy in modern society.
This is an abbreviation of what they have to say about testicle size..
Our testicles aren’t as big as those of chimps and bonobos, but our ejaculation is about four times as big in terms of volume. The theory is that when males compete on the level of the sperm cell, they develop much larger testicles, because in promiscuous animals, the sperm of the different males is competing with the sperm of other males to get to be the first to the egg. And the fact that our testicles are not as small relative to our body as the monogamous gibbon or gorillas reinforces the idea that we have been non-monogamous for a long time.
Plus the design of our penis strongly suggests that it evolved to create a vacuum in the female reproductive system, thereby pulling out the semen of anyone who was there previously. There are all kinds of indications of sperm competition in the human male. And one of the things that we suggest in the book that no one else has suggested is that because the testicles are genetically the part of the body that adapts fastest to environmental pressure, it’s quite possible that our testicles are much smaller than they were as recently as fifteen or twenty thousand years ago, to reflect the historical cultural imposition of monogamy. And of course we all know that sperm count is dropping precipitously even as we speak.
Read an interview with the authors here.