[M]aybe some lefties do reject the heritability of IQ on ideological grounds. I want to make another point – that there’s no need for them to do so. You can accept that IQ (or ability generally) is heritable and still be a strong egalitarian.

I say this because of a simple principle: luck egalitarianism. This says that inequalities are unjust if they are due to circumstances beyond one’s control. If we grant that ability is inherited, then differences in ability are obviously a matter of luck. Insofar as these give rise to inequalities of income, a luck egalitarian can thus claim they are unjust.

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That said, there is a sort of leftie who would be discombobulated by the heritability of ability. I’m thinking of that sort, like Tessa Jowell, who – in their optimism about the malleability of humankind – think that education can significantly reduce inequality.

But that leftism isn’t mine. I agree with Ed Smith that social mobility – even if it could be achieved – is an unattractive ideal. It’s no substitute for a just society.

Peter Singer made a related argument in A Darwinian Left: Politics, Evolution, and Cooperation, suggesting that the left needs to incorporate an updated understanding of the malleability of human nature into its framework – although Singer’s arguments focused on our tendency to cooperate.

Arnold Kling suggests the discombobulation of some on the left comes from the need to maintain a narrative:

In the three-axes model, progressives want to squeeze every issue into an oppressor-oppressed narrative. To suggest that ethnic groups differ in average income for reasons other than oppression would be to weaken that narrative. So even if from a policy perspective a belief in heritability is tolerable, from a narrative perspective a book like The Bell Curve represents a huge threat.

My sense is that this produces a great deal of cognitive dissonance on the left. I have many friends on the left, and I do not know a single one who would instinctively deny the heritability of intelligence. On the other hand, they have been instructed to regard Murray and Herrnstein as vile racists.

My own experience is that plenty of people are willing to argue whether behavioural traits are heritable. I sense Kling’s narrative story is part of the reason, but I also suggest that it comes from a general unwillingness of people to concede any points in a debate. (Does this “bias” have a name – or is this just a manifestation of confirmation bias or a desire to reduce cognitive dissonance?)

Take arguments about climate change. Many libertarians or conservatives fight at every step of the way – the earth is not warming, the warming is not caused by human activity, the warming will be mild, the warming will be beneficial – all this before they get to arguments about the costs and benefits of different policy responses. Yet, whether warming is occurring or harmful would not seem to be a core part of the libertarian philosophy. Debates about heritability have a similar character.