The UCL study also found physically punished children were more likely to struggle in school
The study, using data from 19,000 children born in the UK in the early 2000s, also found that teenagers experiencing physical punishment in early childhood were markedly more likely to bully siblings and others or engage in cyberbullying.
The effects of smacking appeared most immediately in behaviour problems among infants, while repeated experience of physical punishment at ages three, five and seven was associated with lower literacy.
You’d need a good investigation into the nature/nurture situation of adopted children. I grew up in an abusive adopted home and only discovered my biological family in my 30s; they were not abusive to the kids they had later in life. It’s been an interesting journey because I rejected my adoptive parents, their morality, their religion, their politics, and their worldview decades ago, but when I met my biological family it was like walking into the home I’d never known I was missing out on. We have uncanny similarities, senses of humor, social/political views, and atheism. Outwardly, you’d look at me and my family and think “became a product of the environment they were raised in”, except I got there without any of the nurture of their home.
There’s some amazing stories of identical twins discovering eachother at later age. I believe the claim there was that it’s among the strongest bonds between humans that there is. You’ve never met before but when you do, it all immediately just clicks.