Genetic and Environmental Influences on Individual Intelligence

1296 Words6 Pages
The evidence for genetic contribution to individual intelligence are (1) Family studies indicate that intelligence occurs in families, (2) Twin studies illustrate a greater link within identical twins in IQ than between non-identical, or fraternal , twins. This is true even when identical twins raised apart are contrasted with fraternal twins reared together. (3) Adoption studies suggest that adopted children are slightly comparable to their biological parents in intelligence.
The focus here is on differences and similarities and the extent in which they are created by genetic effects, in contrast to environmental influences. Because family components are genetically similar, traits found within that family can be reasonably designated as
…show more content…
So, twin studies suggest that genes play a very important role, but are not the only factor, since if they were; the correlation between identical twins would be 1.
Identical twins raised in separate environments are almost as similar in "g" measurements as those raised together. Adopted children and their adoptive parents have a "g" correlation of zero, of course, while adopted children and their biological parents are likely to have the same correlations as any parent –child set. So although genes do not seem to be the sole factor mediating intelligence, their effects do seem to be unvarying and likely not superseded by environment.
In this way, twin studies give psychologists greater insight into the role of genes in intelligence. Critics of twin studies suggest that twin similarities may be a result of chance rather than evidence of heredity at work. Also, because adopted twin children tend to be placed in similar settings, critics suggest that the trait similarities may be a matter of comparable experience rather than one of heredity.
Adoption studies allow psychologists to decide on the influence of genetics and environment on human development by determining whether adopted children are more like their biological parents, who provide their genetic makeup, or their adoptive parents, who provide the environmental influences. These studies show that
Get Access