Testosterone? Or are some of us just born more aggressively competitive than others? I know I was. I competed in horse events as a girl, then at 17 I started rally driving. Progressed to hillclimbs and club events, Formula Two, Formula Vee. I held an International Race Licence in the early '80s when you actually had to be tested for it on 3 different circuits, the judges being drivers of note such as Leo Geogehan. Wish I'd had the money to go further. The RTA instructor who helped me up off the ground after the awful disaster at the pre-learners where I virtually wrote off the RTA's GN Suzuki (who cares, it wasn't like it was a Norton) is a lady racer. She rides a Suzuki 1000 or something. She knows of several other women who race bikes. I'd like to have a go - if I can get past this slight obstacle - the licence!! P.S. And I can assure you I don't have any testosterone! I do have that dangerous combination of oestrogen + a gun though.
I'm sure some of us have an adrenalin addiction. But with a lot of us guys it's the testosterone talking first. You only have to observe the way some young guys handle that emotion enhancing drug, alcohol.