This new study examined 227 pairs of twins:
They found that the twin who experienced stricter or harsher treatment and less emotional warmth from parents had a greater chance of showing aggression and a lack of empathy and moral compass—a set of characteristics known as callous-unemotional traits.The researchers conclude that the study provides compelling evidence that parenting matters.
They might be right, but the scientific literature indicates parenting has little long-term effect on behavior. Overall the long haul, genes simply dominate.
The scientists fail to mention that, in their discipline style, parents might be reacting to differences in the twins' behavior. Identical twins turn out different because of accidental events that happen during development. For example, one twin could get fall and get a brain injury which worsens his behavior, and parents might react more harshly and coldly to such behavior. One might ask why would a parent systematically treat one twin different than the other? The obvious answer is that the twins diverge first, and then parents treat them differently second. Parents typically delay punishment until the child seems old enough to understand it.
One the other hand, if it is true that there are short-term benefits to more parental warmth and more moderate discipline, that is not without value. I have 6 children and spend a lot of time managing them. If there are techniques that get my kids under better control, that is awesome even if it doesn't change their long-term character.