There's been an unedifying row between Ezra Klein and Sam Harris about race, IQ and genes. I'm not sure this gets to the nub of the matter.

To see my point, let's assume that the most provocative claims made by Charles Murray in The Bell Curve are correct. As summarized by Harris these are: that "general intelligence" is a scientifically valid concept and can be measured by IQ tests; that IQ is highly predictive of success in life; that mean IQ differs across populations; and that IQ is partly genetically determined.

Many of you will find this assumption heroic. IQ has a big environmental factor: it can be increased by schooling, better diet and by less pollution, poverty or oppression. The extent of heritability is questionable. The link between IQ and income is dubious, and that between IQ and wealth even more so. And as Charles Manski has pointed out, even if heritability of IQ is large, and IQ is an important cause of poverty, it does not follow (pdf) at all that anti-poverty policies are ineffective.

For the sake of my argument, though, let's put aside these doubts. Even then, the race-IQ-genes agenda tells us little. I mean this in four ways.

First, a correlation between IQ and success in life tells us nothing whatsoever about the justice or not of an economic system.

I suspect there was such a correlation in medieval China thanks to its civil service exams, or in the Soviet Union: it probably took a lot of cognitive skill to rise up the byzantine bureaucracy. Few, though, would consider those to have been just societies.

In fact, it might well be the case that in a just society the IQ-success correlation is lower than it is in unjust ones. Dictators want underlings to have sufficient cognitive ability to take and implement orders - IQ need not mean having a rebellious mind - which will generate an IQ-success correlation. In free societies, however, we reward people according to many criteria of which IQ is only one. Joey Essex, Paris Hilton and the Kardashians probably do better in capitalism than they would under communism, but they drag down the IQ-success correlation.

Whether capitalism is just or not not is, then, a question wholly separate from any link it generates between IQ and success.

Secondly, there are countless natural genetic differences between people which do not yield large systemic inequalities: eye colour, hair colour, footedness, and so on. None of these are thought to betoken differences in moral worth, so why should IQ be different?

And there are other genetic differences which produce moderate economic inequalities but not ideologies that defend them. Tall men earn more than short ones, but (moderately) short men haven't endured centuries of oppression, stigma and belief in their "natural" inferiority as women and blacks have. Why are race and gender differences different from other genetic differences? The answers lie in history and social science, not in genetic science.

Thirdly, even if we concede that blacks have a lower average inherited IQ than whites, this explains only a fraction of the inequality they experience. Would Stephon Clark have been able to dodge the 20 bullets the police fired into him if only he'd had a higher IQ?

In both the UK and US, black men earn less than whites even if we control for observed ability. Economists at the San Francisco Fed wrote recently:

A significant portion of the wage gap between blacks and whites is not traceable to differences in easily measured characteristics, but rather is unexplained within our model...Perhaps more troubling is the fact that the growth in this unexplained portion accounts for almost all of the growth in the gaps over time.

Put it this way. Imagine two men of identical intelligence. One is born into a poor black family, the other into a wealthy white one. Which has the better chances in life? Differences in outcome depend upon opportunities as well as (and perhaps more than) than ability. As Arsene Wenger said:

Can you name one Formula One driver from an African country, apart from South Africa? And can you really imagine that there is not one guy in Africa with the talent to be a Formula One driver? Why are they not there? Because no one has given them a chance.

What's true across countries is also true within them.

There's something else. Insofar as inequalities between people are due to inherited genes, one big philosophical theory says this justifies their elimination. Luck egalitarianism says that inequalities that are due to luck should be neutralized. On this view, a good genetic inheritance - being a matter of luck beyond one's control - entitles you to no more than anybody else. In fact if we combine this view with Murray's hypotheses, there's a case for redistributing income towards blacks.

Few of Murray's supporters, however, favour this. From one perspective this is odd. The question of the validity of luck egalitarianism is logically independent of the truth or not of Murray's claims. On logic alone, therefore, we'd expect to see some luck egalitarian Murrayists arguing for income redistribution towards blacks.

So why don't we? Nathan Robinson suggests one reason. The function of Murray's research, he says, is to exonerate whites for the suffering of blacks, because it blames this upon nature not society.

But of course, this is false. I'm not sure this is a case for closing down research into genetic differences between races. It's just that we shouldn't pretend that such research tells us anything about what to do about inequality. It doesn't.