Some of the science "speak" in this research paper is a bit beyond me, but it appears to confirm that some "tendencies" are genetic, which doesn't surprise me. I've had dogs brought up the same way, but with very different "temperaments". A lot of "aggression" in dogs ( a bit of a simple term for a range of reactions ) is fear or anxiety-related.

http://www.eurekalert.org/pub_releas...-fvc081016.php

https://www.google.co.uk/url?sa=t&rc...KJi-jyH_nbzI1g