This makes me curious

Apparently it could change depending on environmental factors and diet. So yeah, they can, but I guess you could say it isn't required. (I hope I've done a service to the internet.)

I was just wondering this earlier...for no reason at all

I just read a book about twins

I'm an identical twin. We're both girls, but she's two inches taller than me. So I think if we had dicks, they'd be different sizes x