[diehunde]

How can be almost always symptomatic but at the same time run in some many members of the same family? When you go to see a psichiatrist one of the first questions the ask is if there's history of mental illness in the family.

[slothtrop]

That's still not causation. A history of depression doesn't mean these members all had inherent brain misconfigurations. The brain's chemistry is not static in the first place. There could be afflictions, deficiencies, environmental conditions or cognitive biases spanning generations that could lead to these issues. Everything we experience is expressed as a chemical reaction in your brain, whether you're happy or sad. No one looks at an ecstatic person's brain and assumes they're wired to be ecstatic. Grief and depression can run long.

By virtue of the success rate of therapies such as CBT and others, the evidence for inherent "bad" brains runs thin.