Can this be backed up statistically ? Can a born genius have their spark extinguished by adverse circumstances or poor parenting ? I feel the exceptional ones march on their way to genius despite family support.
I will also add that it is the curse of parenting that you cannot re-do the experiment. And so every choice you make, strict/lenient, forbid/allow, debate/fiat, talk/not-talk is full of questions about whether or not it would be better for your child if you acted in a different way. It is really stressful on the parents.
The best example I can think of is Chris Langan[1], though we only know who he is because he maintained some form of recognizable intellect in spite of his upbringing. Had his beatings led to debilitating psychological problems, brain damage, homelessness, or other things of that nature, we wouldn't be recognizing him as someone held back by his early childhood. Which sort of shows the inherent selection bias.