My opinion is that curve is (at least sometimes) environmental. When I was little, I used to wear tighty-whiteys and wore my little man pointed up. (it was less uncomfortable when it got hard) back then it was straight but had a slight upward curve. As I neared my teens, it got so an erection tried to peek out the top of my drawers and was pretty obvious, so I had to start tucking it down. Now it curves to the left a little and down a little.
While using a vibrator on my wife, I noticed she is a little crooked, too. In fact, when we're in the missionary position, she's got almost exactly the same offset as me. But sometimes-in doggie position-she tries to tell me I'm crooked when I can clearly see I'm lined up dead-straight behind her. I suppose what I lack side to side in doggie, I make up for with my slight downward curve.
I gotta ask...how many of you ladies are a little crooked, too?
Wayne.