It turns out that nurture is not nearly as powerful as people think. Once you pass a fairly low threshold of parenting quality, so that the child is not abused or neglected, parenting has very little impact on how children turn out:
The most prominent conclusion of twin research is that practically everything—health, intelligence, happiness, success, personality, values, interests—is partly genetic. The evidence is straightforward: Identical twins are more similar than fraternal twins in almost every way—even when the twins are separated at birth. But twin research has another far more amazing lesson: With a few exceptions, the effect of parenting on adult outcomes ranges from small to zero. Parents change kids in many ways; the catch is that the changes fade out as kids grow up. By adulthood, identical twins aren't slightly more similar than fraternal twins; they're much more similar. And when identical twins are raised apart, they're often just as similar as they are when they're raised together.
Source ( Short, general interest newspaper article, read the whole thing )
More evidence for this comes from recent research ( long complicated academic paper ) on wealth across generations in England over the past thousand years. When last names were first assigned, they were closely correlated with your economic status. At first, people with 'artisan names' like Baker and Miller did not show up at all as Oxford students or in wills of rich people. But over time, these names started to appear in the ranks of rich people, until the fraction of rich people with these names was equal to the fraction of the general population with these names. Meanwhile, names that appeared only among the Norman conquerers went from being a big fraction of the rich to a normal fraction.
In other words, there was quite a bit of social mobility. Poor people got rich, and rich people became poor, exactly what you would expect if earnings were mainly based on genetics and not upbringing. The process took generations, but over time the rich families were not able to maintain a privileged position. The money, education, and connections people inherited during childhood did not change things very much.
This paper claims that social mobility, as measured by names, has actually gone down in recent centuries. If this is true*, it could mean that rich parents have gotten better at raising their kids, increasing the effect of nurture.
Of course, if science ever advances to the point where people can directly control the genetics of their children, this question of nature versus nurture becomes meaningless. But until then, there is a big pile of evidence showing that
you can lighten up a lot without hurting your kids.
Serenity Parenting changed our lives. We used the Ferber method—let the kid cry for 10 minutes, briefly comfort him, repeat—to get our twins to sleep through the night. We enrolled them in an activity or two, but they spent a lot more time watching cartoons while we relaxed. Our family specialized in activities that were literally "fun for the whole family": reading books together, playing dodgeball in the basement, going to the pool for a swim. If "Lighten up" was the only practical lesson of twin research, my reading had more than paid for itself.
*The paper has several problems, and makes more claims than the data can support.