Petter Bøckman and colleagues at the University of Oslo in Norway published their major findings on human sexuality in the journal Apollon on Jan. 29, 2014, to announce the new anniversary exhibition Sexus at the Natural History Museum at the University of Oslo.
One of the major findings published by the researchers is that fidelity in human females is related to the size of their partner’s testicles. Larger testicles in human males were highly correlated with higher instances of infidelity in human females.
The correlation between infidelity and testicle size was found to be consistent across the range of pledges of fidelity that included open relationships and those ostensibly governed by moral precepts.
The behavior is an adaptive trait that promotes the highest likelihood of having offspring and the interest of the female in producing the healthiest offspring possible.
Bøckman claims that “the less faithful the female, the larger the male’s testicles.” This maxim holds true in all primates.
Lest men lose heart and faith in their mate, the researchers also note that brain size is just as important to women seeking a mate. This attribute of humans is considered to be similar to that of female elk seeking out a mate with the largest antlers. Human females look for brain size through conversation and other behaviors prior to mating.
The researchers do not claim that brain size and testicle size is all there is to female fidelity or mate selection. The research is centered on a Darwinian adaptation and selection approach that favors these two attributes.