The only eugenic process Natural Law relies upon is markets. in other words, if you (your family) is self supporting, and not engaging in irreciprocity, we have no other means of testing your fitness other than demonstrated fitness.
If you (your family) is not self supporting, an engages in irreciprocity, no matter your excuse, then you are in fact, demonstrating unfitness.
Fitness being akin to “good” – anything not unfit, is fit. Fitness remains undecidable (only demonstrable) because of the causal density and unpredictability of future outcomes. But unfitness remains a provisional known (a known subject to being updated with new information).
This the demarcation between HARD eugenics (attempting direct control over natural eugenics) and SOFT P-Eugenics would be “anything not unfit remains fit (a fitness candidate) – or rather, we P-eugenics are achieved by NOT practicing dysgenics.
P-law is via negativa, meaning do not reproduce dysgenically, it is not via-positiva, meaning culling of people. It does leave open the possibility of termination for catastrophic birth defects. We don’t answer the question of abortion because it is undecidable under law. It is only decidable within a polity.
P-law does not prohibit genetic innovation (Transhuanism) as long as it reversible in the next generation and warranteed.
The generational sink in testosterone levels as far as I know, is almost entirely due to failure to exercise and engage in dominance play, and can be restored by physical activity – we know this because we see people do it every day. THere is some negativity to BPA and other chemicals but tis is as easily rectified as requiring all foods to be shipped (more expensively, and less environmentally costly ) in glass containers.
Drop in testosterone relates to prolonged.low level stress, or rather a higher baseline stress level – for example the constant stimulus of living in urban centers, or prolonged financial stress…i.e. anomie
Also – occupations that have intermittent physical stress coupled with enough recovery time, tend to elevate testosterone. for example: jobs which include physical exertion but don’t include “taking work home with you” (no worrying about after hours.)