However, both populations experience suboptimal access to energy, and consequently maintain minimal levels of body fat and low BMI
You are citing a malnourished population.
Previous studies of non-western populations have revealed inconsistent associations between men’s testosterone levels and paternal or marital status. | Twenty-seven Hadza participants | Eighty Datoga participants
This is a comparitively small study, and one which contradicts other bodies of research.
As with male birds, it seems likely that testosterone facilitates reproductive effort in the form of male–male competition and mate-seeking behaviour, both of which interfere with effective paternal care.
Given the increasing social atomisation of the west (see:average age of fatherhood, number of children had, divorce rates), the hypothesis proposed by this paper implies testosterone levels in the west should be increasing not decreasing.
Look, I get the desire to debunk redpillers, but when we’re talking about a worldwide trendline in basic biology you’re going to need more research than this to do so. The Male infertility crisis is a genuine problem field experts are extremely worried about, hence the need for research and coverage by the mainstream (to stop snake oil salesmen being the main point of contact for this issue).