6. IQ scores of identical twins tend to be more alike than those of same-sex fraternal twins. This might be taken as very good evidence for a hereditary effect. On the other hand, which of the following possible findings would give the best evidence AGAINST such a conclusion?
Parents treat identical twins more alike than they do fraternal twins
Identical twins are typically born into middle-class families, where they both are provided with stimulating environments
when adopted, all twins scores become more similar to adoptive parents and less like biological parents
Identical twins tend to have similar achievement test scores