My wife recently gave a presentation on the book 'Rise & Fall of the Third Chimpanzee' by Jared Diamond. Diamond would argue that if aliens were to figure out earthly animals' sexual fidelities, they would conclude that humans are mildly polygynous - because an average man is slightly taller and broader than a woman of that society. Though not a very convincing point, he would proceed the discussion as to how the species' mate-loyalty can be deduced by the size of the male versus female in that society.
In a slide that discusses this aspect, my wife typed 'Mindly Polygynous' instead of 'Mildly Polygynous' (which now stands corrected) and a friend promptly asked if it was a Freudian Slip and the whole crowd started giggling at me. Just a thought: when it's a man's fidelity that's discussed in a crowd in a somewhat conservative society, it can be treated as a joke; but I'm quite sure that had it been a woman's fidelity questioned in a similar society, the discussion would have assumed serious proportions. If you want to understand the paranoia associated with a woman's loyalty to her partner, read the book, or at least go through the slides which are fairly indicative.