Parents can breath a collective sigh of relief, or may decide to pout, as they take a less intimidating role in the significance they have in developing the personalities of their children. Primarily genes, and to a lesser degree, culture, peer groups and plain ole’ chance seem to influence a child’s personality more than any method of parenting. Identical twins are just as similar regardless of being raised together or independently; adopted siblings are no more similar if they are raised together or apart. Identical twins can be so alike that they may choose to wear a rubber band around the same wrist, find sneezing in elevators to see the reaction of others equally appealing or score very similarly on a battery of psychological testing even when they weren’t raised in the same house. This may sound odd but identical twins being raised in the same household are no more similar than ones being raised apart. Adopted siblings generally grow up being nothing alike whatsoever regardless of having exactly the same upbringing.
Far from being a blank slate that is highly malleable, we come prepackaged with genetic information that contributes to our personality in ways that parenting never could. So, we can stop ruminating about all the times we didn't put Mozart music up to the fetuses ear or how we didn't spend enough time reading to our children in hopes that they might be the next great intellectual of our time. Children's intelligence has much more to do with their genetic predisposition than how stimulating you may have been as a parent. So, what about the importance of having a father in the home or the importance of having two parents of the opposite sex in the household? Does this not make a significant difference in the child's personality, intelligence and success? Nope, it sure doesn't so we can put another point up on the scoreboard for reality and our religious conservative friends that continually harp on the necessity of a father figure and sanctity of marriage are still desperately trying to score their first point.
All of these findings are well-researched scientifically. This doesn’t give parents a license to mistreat their children either. Children remember the way their parents treated them and may be less inclined to help their parents when the script is flipped and the parents need care from the children. Obviously, gross negligence and abuse can leave lasting scars on a person’s life that will affect their interactions with others later in life. This TED video gives a good summary of Pinker's argument. It's based on his 2002 book, The Blank Slate: The Modern Denial of Human Nature.