Because there is far more evidence, both formal, and lived experience for everybody, multiple times per day, that people's environment (including who they surro

Because there is far more evidence, both formal, and lived experience for everybody, multiple times per day, that people's environment (including who they surround themselves with) affect their personality, than there is evidence that it does not. The "newborn saying thank you" comment was a joke, as they generally don't say much when newborn, but illustrative of the point: newborns do not have any expressed personality to speak of, because genetics alone cannot create one. Your newborn has zero personality, but with the right upbringing, and perhaps the right genes, it will have a great one. With just the genes... probably not. tl;dr the claim I am arguing against is TFA's "environment doesn't matter", but I don't claim that genetics don't.