I think this trope comes from a study showing that most (male) criminals actually did have an added Y chromosome. This isn't to say that a second Y is a guarantee, perhaps anymore than statistical data showing drunk drivers frequently had red hair means that being a redhead makes you a drunk driver.*
I'm not sure about how much this relies on Insane Troll Logic, but the aforementioned study has led to the speculation that the connection may be due to more testosterone.
I think this trope comes from a study showing that most (male) criminals actually did have an added Y chromosome. This isn't to say that a second Y is a guarantee, perhaps anymore than statistical data showing drunk drivers frequently had red hair means that being a redhead makes you a drunk driver.* I'm not sure about how much this relies on Insane Troll Logic, but the aforementioned study has led to the speculation that the connection may be due to more testosterone.
And if you're wondering, there's an article on this condition from That Other Wiki: http://en.wikipedia.org/wiki/XYY_syndrome
Edited by Stoogebie