Conrad P. Kottak,
University of Michigan
| cline | A gradual shift in gene frequencies between neighboring populations.
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| descent group | A permanent social unit whose members claim common ancestry; fundamental to tribal society.
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| hypervitaminosis D | Condition caused by an excess of vitamin D; calcium deposits build up on the body's soft tissues and the kidneys may fail; symptoms include gallstones and joint and circulation problems; may affect unprotected light-skinned individuals in the tropics.
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| hypodescent | Rule that automatically places the children of a union or mating between members of different socioeconomic groups in the less-privileged group.
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| melanin | Substance manufactured in specialized cells in the lower layers of the epidermis (outer skin layer); melanin cells in dark skin produce more melanin than do those in light skin.
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| natural selection | Originally formulated by Charles Darwin and Alfred Russell Wallace; the process by which nature selects the forms most fit to survive and reproduce in a given environment, such as the tropics.
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| phenotype | An organism's evident traits, its "manifest biology"-anatomy and physiology.
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| rickets | Nutritional disease caused by a shortage of vitamin D; interferes with the absorption of calcium and causes softening and deformation of the bones.
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| social race | A group assumed to have a biological basis but actually perceived and defined in a social context, by a particular culture rather than by scientific criteria.
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| tropics | Geographic belt extending about 23 degrees north and south of the equator, between the Tropic of Cancer (north) and the Tropic of Capricorn (south).
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2002 McGraw-Hill Higher Education