There is some merit on the overall argument if you look at other animals including primates. But there are various factors you need to take into account besides gonad / penis size, eg are females solitary and hard to find, or do they live in groups. Are males bigger than females (sexually dimorphic) which would indicate higher competition between males typically found in a poly / harum society. Also how loyal females are. For example chimps have massive genitals compared to gorillas. Both are poly but Gorilla males are much larger than females unlike chimps. But females are loyal so no massive gorilla balls and long penis needed to compete with other male sperm. Humans are a bit of an anomoly. They have the biggest penis of all primates. Sexual dimorph is kind of in the middle. And sexual behaviour is overwhelmingly monogomous. Skeletons show there was a big difference in male to female size until about half a mill years ago indicacting we were harum based at that stage. Fighting over women. Big dicks indicate not that monogomous either. We seem to have kept the big dick but lost the female size difference. But unlike chimps we are monog. That could be down to us needing to adapt because our environment is not as stable as the jungle. TL:DR Bigger dicks in some races imo is therefore an indicator that they are more promiscuous. And vice versa. And it seems to me that asians compared to other races have less sexual dimorph. So less poly.