The debate on nature versus nurture has been going on for quite a long time. You want some links on how environment can change people? I only have to look at my own country how prosperity changed a famed violent-gened country into a model of peace and quiet, but I've read studies about it also, long ago...
Sure, if nothing is triggering the anger. My interest is how different folks act differently under the same circumstances.
I'm sure genes always play some role, but I think it's too easy to make more of the gene expression changes under duress than simply saying someone has a violence-gene.
Or simply blaming culture or upbringing. Genetics alone is complicated enough without the assumption of a "violence gene". Genetics doesn't work that way. Some traits can be repressed by other traits. So even having a particular gene doesn't mean it's going to affect your personality.
Still, from birth, how much control do we actually have over ourselves? Where's the line between the person we will ourselves to be versus the person we're programed to be? I suspect genetic programming plays a larger roles than some folks would like to admit.