So, one technical way of putting it is that shared environment doesn't matter at least for children in well-off or middle-class families. But there's a more radical way of making this claim and this is that parents don't matter or actually parents do matter but they matter just because they typically contribute to genetic material that makes up a child. Parents and parenting practices don't matter. They don't play a reliable role in shaping children's intelligence or their personality. This was the claim made and developed based under behavioral genetics data by the psychologist Judith Rich Harris, in her book "The Nurture Assumption" subtitled why children turn out the way they do. Parents matter less than you think and peers matter more. So, Harris acknowledged that roughly half of the variation in various traits is caused by the genes, but since the other half isn't due to shared environment, she looked at peers and peer groups as a reliable source for human differences. This is a controversial interesting claim because there's other aspects of non-shared environment including random events that may cause the difference. But this might seem like a shocking claim. You might be thinking there must be an effect of shared environment. Of course parents have an effect, after all there are a million studies as well as common sense showing that there's a high correlation between parent and child for everything. Parents who read a lot have children who read a lot. Religious parents have religious children, criminals have criminal children, rich parents have rich children, smart parents have smart children and so on and so forth. These are obvious much replicated findings. But the problem is, they're consistent with multiple explanations. So, it's possible that all of the shared environment data is wrong and that good kids have good parents because parents do something that affects their kids. But it's also possible that we know this to be true that parents share their genes with the kids. Since children are typically raised by people who share their genes, it's impossible to point to dissimilarity between parent and child and says to the environment. It could be that the environment plays no role at all. Finally, there's something called child effects which is that the child could be making the parent's good not vice versa or making the parents bad. So, for instance, children who are spanked tend to be more violent. Now, one possibility is there are genes that make parents likely to spank and children likely to be violent or genes that proposed people say to low impulse control lean both to the spanking of bad behavior. A second possibility maybe the one that most people believe is that parents spanking their kid makes her kid meaner. But a third possibility is if you have an aggressive and violent kid, you're more likely to spank him or her and that will be a child effect. Parents might read a lot more to intelligent and inquisitive kids and this could be because they share genes, it could be because the reading makes children more intelligent inquisitive or it could mean that if you have an intelligent inquisitive child, you're just more likely to reach to that child as an effect of the child, not to genes and not the not the parental behavior. So, when you see similarities and when you see effects, you have to think about the different alternative explanations for this. I'll give you an example of this. One I think is probably the worst study in the world. I won't single out the investigators, I'll just give the headline as reported in popular press. Showing that family meals help teens avoid smoking, alcohol, drugs or as one summary put it, the most important thing you can do with your kids, eat dinner with them. So, here's the exercise, you have the finding which is that kids who have a family meal with their parents are less prone to take drugs. How could you explain it? The way the article explains it is that a family meal makes kids less prone to take drugs. But, we could sit here we can easily think of multiple alternative explanations. One possibility for instance is it's the other way around which is that if your kids don't take drugs and they're just good kids and they hang around a house wall or friends, take drugs and have a good time, they're more likely to be around for family meals or it could be a third factor which is there are good families and bad families. Good families tend on average to raise kids who don't take many drugs and also have family meals while bad families have kids who were stoned all the time and don't have family meal. Even if there's no relationship at all between the drugs and the family meal. This is in the same sense that cities that have large populations have many churches and many bowling alleys and cities with small populations have few churches and few bowling alleys. It's not that there's a connection between churches and bowling alleys, rather they're both the byproducts of a single effect which is the population of the city. Finally, in this particular study, they didn't factor out age. So, what the study might actually be finding is that 12-year-olds are more likely to be drug free and have meals with their family while older kids, 17-year-old are more likely to take drugs and have no family meal. The effect could be driven by the age difference and have nothing to do with any sort of relationship between drugs and family meals. But you might still be unhappy with this. Particularly if you're of a certain age you might be certain that your mom and dad had a huge role in your life. You might think that's why you're so happy and successful or you might think that's why you're so miserable and screwed up. But I would ask, how do you know? How do you partial out genes versus environment? Are you adopted? If you're not adopted then you have no way of doing irrelevant parceling. You have no way of knowing whether dissimilarity or defects of your parents is due to genetic overlap are due to environment. Even if you are adopted, it's difficult to figure out what's cause and what's effect. Suppose your parents treated you poorly and you were depressed and anxious and troublesome child, was it that they treated you poorly and they made you so or did they treat you poorly as a response to the way you were. Now, sometimes people freak out at this point and they might say "Look, if parents don't mold their children's personalities which is what the behavioral genetics data suggests, why should they ever treat their children nicely?" I find this a very very weird claim but people make it so I have to address it. One way to realize that it's weird is most people believe that we don't mold our spouses and lovers and romantic partners' personalities. Does that mean we shouldn't treat them nicely? Well, of course it doesn't mean that. Parents treat their children nicely and they should treat their children nicely for the same reason you should treat the people you love nicely because you love them, because you want them to be happy, because you want to have good relationships with them. Being a good parent or a good friend or a good spouse or lover is not at all contingent on believing that your actions will transform their personality and intelligence. I think there's a lot more research to be done in this area and we might discover that the conclusions and I'm confidently raising right now turn out to be false and that there's more going on. But at this point, we have to live with one of surprising conclusions have come from behavioral genetics and from psychology more generally. Which is that parenting doesn't matter anywhere near as much as people believe it does.