One theory blames oxidative stress, caused by the onslaught of nasty molecules known as free radicals.

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Ilan Meyer, a senior scholar at UCLA's School of Law, offers an explanation for these disparities through the "Theory of Minority Stress, " which suggests that these health inequities may be rooted in discrimination, with negative health behaviors acting as coping mechanisms for repeated exposure to stigma-related stress.

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Another theory has to do with stress reduction.

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Class.com, for example, is considering different biology classes that stress creationism or evolutionary theory to appeal to Christian fundamentalists or secular families, respectively.

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Even if our basic theory is that economy is elastic in response to nominal stress and plastic in response to real stress, a sudden change in rigidity combined with a large nominal shock could cause a very large plastic deformation in the economy.

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According to Dr Sinclair's theory, which he calls xenohormesis, animals rely on such botanical stress signals to give them extra information about their own environments, in the same way that the alarm calls of one species warn others of danger.

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Support for that theory - there's a spike in kids being treated for repetitive-stress injuries.

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However, all the researchers involved are keen to stress that their finding falls a long way short of proof for this theory.

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