Jews is just a a group of humans with certain statistical properties. Science could "exist" without them, no test necessary - they are not a magic ingredient. They did constitute very significant part of Russia's science establishment (despite quotas) and Russia was arguably #2 science producer in math and physics, and this % of their scientists and teachers leaving might plausibly knock them down a few levels. But Russians are certainly plenty smart - Mendeleyev, Kolmogorov, Gamow, etc. etc.