What kind of twin studies have been done around IQ?

Here's a sample of what I found by Googling twin study IQ

http://www.newscientist.com/article/dn1520-iq-is-inherited-suggests-twin-study.html

http://wilderdom.com/personality/L4-1IntelligenceNatureVsNurture.html

http://www.lrainc.com/swtaboo/taboos/tjbouc01.html

http://everything2.com/index.pl?node_id=1162493

http://www.vdare.com/Sailer/pioneer.htm

http://en.wikipedia.org/wiki/Minnesota_Twin_Family_Study

There are some fascinating studies concerning twins IQ and homosexuality as well as birth order. Just google twin IQ studies.

Twin studies have been widely conducted to investigate the heritability of intelligence, specifically measured by IQ (Intelligence Quotient). Here's an overview of the different types of twin studies conducted in this field:

1. Classic Twin Studies: These studies analyze the similarities in IQ between monozygotic (identical) twins and dizygotic (fraternal) twins. Monozygotic twins share 100% of their genetic material, while dizygotic twins share approximately 50% of their genetic material. By comparing the correlation of IQ scores between these two types of twins, researchers can estimate the genetic contribution to IQ.

2. Adoption Studies: In these studies, researchers compare the IQ scores of adopted children with their biological parents and their adoptive parents. By separating the influence of genetics (biological parents) from environmental factors (adoptive parents), researchers can estimate the relative importance of genetic and environmental factors on IQ.

3. Twin Kinship Studies: These studies involve comparing the IQ scores of twins raised together (concordant) and twins raised apart (discordant). By comparing the concordance rates between these two groups, researchers can deduce the influence of genetics and environment on IQ.

4. Twin Resemblance over Time: Longitudinal studies are conducted to compare the stability of IQ scores between monozygotic and dizygotic twins at different ages. This helps determine the degree of genetic and environmental stability in maintaining IQ scores throughout a person's life.

It's worth noting that while twin studies provide valuable insights into the heritability of IQ, they cannot entirely separate genetic and environmental influences. Other factors, such as prenatal environment, epigenetics, and non-shared environmental factors, also play a role in shaping an individual's IQ.