Effects of Heredity and Environment on Intelligence
By T. M McDevitt|J. E. Ormrod
Pearson Allyn Bacon scholar Hall
It is often difficult to separate the relative influences of heredity and purlieu on human characteristics. People who realise similar communicable makeup (e.g., brothers and sisters, pargonnts and their children) typically live in similar purlieus as well. So when we see similarities in IQ among members of the same family, it is warm to know whether those similarities argon due to the genes or to the environments that family members share. Nevertheless, a world-shaking body of research tells us that both heredity and environment affect intelligence.
Evidence for Hereditary Influences
Earlier we mentioned that measures of information treat speed correlate with IQ scores. Speed of processing depends on neurological efficiency and maturation, which are genetically controlled. From this standpoint, then, we have rough support for a hereditary basis for intelligence (Perkins, 1995). The situation that children with certain genetic defects (e.g., Down syndrome) have, on average, signifi housetly set rough IQ scores than their nondisabled peers (Keogh & MacMillan, 1996) provides further severalize of hereditys influence.
But perhaps the most convincing evidence comes from twin studies and adoption studies.
Numerous studies have utilize monozygotic (identical) parallel and dizygotic (fraternal) twins to get a sense of how strongly heredity affects IQ. Because monozygotic twins go about as a single fertilized egg which then separates, they are genetically equivalent human beings. In contrast, dizygotic twins are conceived as two separate fertilized eggs. They share about 50 percentage of their genetic makeup, with the other 50 percent being unique to each twin. If identical twins have more similar IQ scores than fraternal twins, we can reasonably conclude that heredity influences intelligence.
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