The extreme strength of jealousy in patriarchal societies is due to the fear of falsification of descent. This may be seen in the fact that a man who is tired of his wife and passionately devoted to his mistress will nevertheless be more jealous where his wife is concerned than when he finds a rival to the affections of his mistress.
Source: Marriage and Morals, 1929, by Bertrand Russell
More info.: https://russell-j.com/beginner/MM03-010.HTM