What kind of twin studies have been done around IQ?

Answer 1

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

Answer 2

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