What Hereditary and Environmental Factors Impair Intelligence?
One-fourth of all mental retardation reflects a problem developed before or during birth. Premature birth, the health of the mother, proper care at birth, injuries during the birth process, mothers use of drugs and exposure to diseases of the mother such as syphilis and rubella are common causes of developmental delays and mental retardation. Several genetic syndromes may lead to retardation including Down Syndrome, a common genetic syndrome resulting from extra chromosomal material, 47 rather than 46 chromosomes. One-half to three-quarters of mental retardation do not have known biological or genetic causes. Research has revealed that children exposed to disadvantaged living environments and denied normal opportunities for stimulation and education may develop retardation. Children from low-income homes may become discouraged and not utilize the intellectual talents they have, displaying less intelligence than they have, scoring lower on IQ tests and creating low expectations in their
