yes, I agree with you. It's just at the time I was unaware that brain chemistry could be genetically dependent; although as you say that's pre-disposition, and the trigger can be trauma, and sometimes knowing you are adopted can be the source of that trauma, thus triggering the behaviour.

Trauma is deeply intertwined with genetics.

For instance parents who have genes that increase impulsivity are more likely to e beat their kids exposing them to trauma, the kids are more likely to do dumb things that expose themselves to trauma, and the kids are more likely to do impulsive things like try drugs.

So it's hard to disentangle what portion of the effects of trauma are direct and which are confounds.