An important one was protection from disease, suspected to be a consequence of the increased risk of infection that living in settlements brings.

ECONOMIST: Human evolution

"Whether that has anything to do with protection against disease has not been proven, " says Kevin Ault, a professor of obstetrics and gynecology at Emory University who consults for both Merck and Glaxo.

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Only then could doctors truly point to better dental care as protection against heart disease.

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Japanese consumers are said (by politicians and bureaucrats, that is) to be either indifferent to how such protection reduces choice and raises prices, or to support protectionism because they fear contaminated and disease-bearing foreign products, and the vulnerability of Japan to blockages of agricultural product imports.

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The reason, according to those ponderers, is that the genetic diversity promoted by sex is a protection against disease.

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Breast-feeding can certainly help provide immune protection against multiple illnesses, but not if a mother does not have immunity to a certain disease such as pertussis.

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And foreign-born children whose parents were also born outside of the United States seemed to benefit from additional protection from these conditions: 18% of these children developed allergic disease compared with 33% of foreign-born children whose parents were born in the United States.

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