Re: What´s the problems with twin-studies to dicide upbringing vs genes?

The main problem with twin studies is that it is rare to have a case where 
monozygotic (identical) twins are separated.  Without separation it is not 
possible to compare nature to nurture and some of the only people to do 
twin separations on purpose were the Nazis and I think the Americans also 
did some on multiple births. 

It is difficult to measure differences in personality because people don't 
really like qualitative tests.  You can't really say twin A is a 50% more 
angry person than twin B.  This doesn't mean that twin studies should be 
ignored.  Where twins have been separated there are often incredible 
similarities between the choices the twins make.