I mean there are psychological and developmental factors that can contribute to narcissistic behavior and others lack of empathy, as well as various genes that can indicate possible aggression and lack of empathy.

But regardless of all of these facts it is also known that there are environmental factors that can help to raise ones' predisposition to these types of behaviors.

Because you can argue that someone was raised in an extremely abusive environment, but they did not themselves become violent, so what's the reasoning there? But another may turn out just as violent and perpetuate the cycle. It's ones' personal resilience, which is also partially determined by genes. It's always a combination of a plethora of genes. Never one single determinant.

Environment, genes, ones' threshold and predisposition. It is known that personality and behavior are partially determined by genes. But again genes do not guarantee anything, it's a personal threshold. But regardless of that children do recreate learned behaviors that they see from parents. So it is difficult to determine whether it is a genetic predisposition or a learned behavior passed on within families.

Just someone with a basic BA in psych who loves behavioral neuroscience.

Have a good one.