I believe he refers to the fact that all "important" positions are selected from the bottom/top tier. We don't imprison random people from the population, we i

I believe he refers to the fact that all "important" positions are selected from the bottom/top tier. We don't imprison random people from the population, we imprison the most aggressive (in case of violent crime at least). We hire people with top IQ for engineering and science related endevours. We promote people who work the hardest ("industriousness") The most ambitious people get the top jobs. It doesn't matter if on average two groups are the same for those qualifiers, if only the top 1% are selected, then you would expect which ever group has the flattest bell-curve distribution (and thus more "on the edge") to be over-represented (whether it is gender, "race", age). If it isn't, then racism/sexism/whateverism is at work. Caveat: with top IQ in engineering, an important factor that only people who "like things more than people" apply, other way around for loads of other fields.