Brad DeLong takes me to task, noting that though "[t]he inheritance of inequality is strikingly large in America today," the inheritance of IQ has relatively little to do with it. Here's math:
If inherited genetically-based IQ were the source of the extra edge that the children of the rich get in our society, than we would expect a parent with 4 times average lifetime full-time earnings--say $200,000 a year--to have a kid with a lifetime average income of $51,500 instead of the average of $50,000. But it is not $51,500. It is $150,000.
True and important, and I didn't want to say otherwise.
What I wanted to inject into this is that while we can change people's childhood environments in a forward-looking way or look at adoption studies for research purposes, in practice most people aren't newborn babies and we're obviously not (and shouldn't!), in practice, going to reassign children to new families. Consequently, the precise degree to which things are inherited "genetically" versus "environmentally" is of limited relevance in thinking about how people deserve to be treated. If you allow a large degree of inequality to exist, then children will grow up in sharply unequal environments, and the people who grow up in those environments will suffer from lifelong disadvantages for reasons that are completely outside of their control.