>>76511579
Less physical labor. That's it. That's all there is to it. Don't listen to the retards telling you about /x/-tier shit like onions or fluoride or whatever. Testosterone production is stimulated by physical activity. People used to live on farms and do back breaking work all day. Then they worked in factories and did the same. Or mines. Or being lumberjacks. Doesn't matter. Nowadays most jobs don't demand any physical activity beyond walking around and thus testosterone production is reduced.

I'm not sure why everyone is treating it as a mystery.