[born yesterday]

It seems reasonable to assume that if sperm count plummets, a man's masculine attitudes and behaviors will also plummet. The fact is that sperm counts are dropping. How would you explain it? What results would you expect?

[Hawkeye's Girl]

Dude, a man's masculine attitudes and behaviors are connected to his testosterone levels, not his sperm count.

Sterile men aren't any less guys than normal men.

[Just another Joe]

It seems reasonable to assume that if sperm count plummets, a man's masculine attitudes and behaviors will also plummet.

This is not correct. The sperm count has nothing to do with masculine attitudes and behaviours.
I think you are thinking about testoterone. Or if you want the opposite hormone, from women, estrogen.

[The Giant Apricots]

What came first?