I think it's the wrong type of question. Things can be 100% heritable or 100% environment, both at the same time.
Classic example: Dad was nearsighted, Grandma was nearsighted, I'm nearsighted. But thanks to the environmental availability of eyeglasses and contacts, I don't have to squint at everything. Plus, my vision was only sorta-kinda nearsighted while in high school, but when I went to college and started doing a lot of tasks that required a microscope, my vision went straight to heck. Microscopy wrecks your eyes, as does sitting in front of a computer the livelong day. So for many, many years, I was legally blind without my glasses: heredity made sure I was going to be at least a little myopic, environment assured that I would be darn near blinded by it. Recently, however, I've been working a lot outdoors, especially at tasks that require tracking small objects at a distance--fishing, watching birds, kayaking, training the dogs off-leash. Last visit to the optician, my eyes have actually improved due to the exercise!
I suspect it's the same with neurochemistry: you're born with some advantage or deficiency, but we know that brains are highly plastic and adaptable to new environments. There's quite a bit of research and literature on the subject--see PubMed for "learned helplessness" and there have been several books written on the psychology of victimhood and oppression, where entire groups of people regardless of genetics are taught to behave in self-destructive ways. There was a JAMA article a couple of years ago that found that people with post-traumatic stress disorder from surviving the Holocaust ended up having their brain chemistry permanently altered in such a way that even their children had changed brain chemistry. And those children did not have PTSD, but somehow they had inherited their parent's stress response. You might have someone with all the cheerful genes who survives, say, a civil war in Rwanda and is permanently traumatized by it, and you might have someone who has none of the cheerful genes but all the advantages money can buy, and so they are comparatively happier than the civil war survivor.
