I don't know about Bonner, but other evolutionary biologists, notably Mark Maslin have reflected on the comparative anatomy aspects of primate genitalia. It's a theme in evolutionary biology since Georges Cuvier's quip "À la vue d'un os, d'un seul morceau d'os, je reconnais et reconstruis la partie de l'ensemble dont il provient" [give me a fragment of bone and I can reconstruct the entire animal]. From certain peculiarities of anatomy you can infer a lot about the life-style - diet, behaviour, inter-personal relations - of the species. Canines for carnivores, flat molars for grinding hay. Sexual dimorphism [usually blokes bigger than women] strongly suggests a bit of polygamy. Although nobody to my knowledge has come up with an explanation of why men have proportionately bigger feet than women - it cannot be all the better for playing soccer with. Humans are defo sexually dimorphic but the size differential is nowhere as extreme as with gorillas so the consensus is that the human default position is
Here's a picture from Mark Maslin zooming in, not on the feet, but the package.
Buster Gonad [R] with their unfeasibly large testicles - that's because they spend an enormous amount of the time bumping their uglies and so need a factory and warehouse for supply to meet demand. Men, not so much; indeed a couple of couplings will deplete the precious bodily fluids to zero and it will take a day or two to replenish. Remember the exhausted Rustico? If you're trying for a baby, it's probably a good idea to a) switch to boxers b) no wastage!
team in 2015 which found the largest primate testicles in proportion to body weight in the scrotum of Mirza zaza [putting it all out there L]the northern giant mouse lemur found in a tiny isolated forest fragment of Madagascar. The species was only discovered and Latin-named in 2005. The team from Bristol Zoo capture-recaptured 5 male mouse lemurs and applied the calipers to their nads. The average volume was 3.9 cc. For a creature that weighs in a trifle under 300g; that's 1.3% of body weight. <TMI alert> I just measured my unfeasibly normal-sized testicles at wid 35mm x len 55mm </TMI> and applied that to the formula used by EJR-M [1/6 * π * w * w * l] to come up with a testis volume of 35 cc - call it 10x the size of Mirza's balls. But, at 70kg, I weigh 200x more than the biggest male mouse lemur. Matt Walker calculates that, for parity of esteem, we'd need Buster gonads the size of grapefruits, That's more or less true but its based on a miscalculation of a misreading of the original paper; from which I attach an excerpt of Table 3: