I’m a bit late to this party, but Pew has a new report about changing views on evolution. The big takeaway is that a plurality of self-identified Republicans now believe that no evolution whatsoever has taken place since the day of creation — let alone that evolution is driven by natural selection. The move is big: an 11-point decline since 2009.

Obviously there hasn’t been any new scientific evidence driving this rejection of Darwin. And Democrats are slightly more likely to believe in evolution than they were four years ago.

So what happened after 2009 that might be driving Republican views? The answer is obvious, of course: the election of a Democratic president

Wait — is the theory of evolution somehow related to Obama administration policy? Not that I’m aware of, but that’s not the point. The point, instead, is that Republicans are being driven to identify in all ways with their tribe — and the tribal belief system is dominated by anti-science fundamentalists. For some time now it has been impossible to be a good Republicans while believing in the reality of climate change; now it’s impossible to be a good Republican while believing in evolution.

And of course the same thing is happening in economics. As recently as 2004, the Economic Report of the President (pdf) of a Republican administration could espouse a strongly Keynesian view, declaring the virtues of “aggressive monetary policy” to fight recessions, and making the case for discretionary fiscal policy too. (Naturally, the only form of discretionary fiscal policy considered was tax cuts, but the logic was straight Keynesian, and could have been used to justify public works programs equally well.)

Oh, and the report — presumably written by Greg Mankiw — used the “s-word”, calling for “short-term stimulus”.

Given that intellectual framework, the reemergence of a 30s-type economic situation, with prolonged shortfalls in aggregate demand, low inflation, and zero interest rates should have made many Republicans more Keynesian than before. Instead, at just the moment that demand-side economics became obviously critical, we saw Republicans — the rank and file, of course, but economists as well — declare their fealty to various forms of supply-side economics, whether Austrian or Lafferian or both. Compare that ERP chapter with the currency-debasement letter and you see a remarkable case of intellectual retrogression.

And look, this has to be about tribalism. All the evidence, from the failure of inflation and interest rates to rise despite huge increases in the monetary base and large deficits, to the clear correlation between austerity and economic downturns, has pointed in a Keynesian direction; but Keynes-hatred (and hatred of other economists whose names begin with K) has become a tribal marker, part of what you have to say to be a good Republican.