It, too, has not been extensively studied.

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Symmetry in particular has been studied extensively, not only in the Western World but also in hunter-gatherer cultures removed from mainstream media.

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"Bird colouration has also been intensively and extensively studied for a long time, " says Dr Galvan.

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For cadmium to be evident in rice grains as well, the soil in which it was grown must have been especially highly polluted, said Jonathan Wong, a Hong Kong biology professor who has studied soil pollution extensively on the mainland.

WSJ: Cadmium-Tainted Rice Found in Guangzhou

For cadmium to be evident in rice grains as well, the soil in which it was grown must have been especially highly polluted, said Jonathan Wong, a Hong Kong biology professor who has studied mainland soil pollution extensively.

WSJ: Cadmium-Tainted Rice Found in Guangzhou