[CamelCaseCondo]

This is an example of how twins give us information when one variable is fixed - genetics. Can reciprocal information be found when observing the opposite: adoptees who share no genetic base but had the same upbringing in the same environment?

[GenBiot]

An interesting idea, but a big problem would be that the uterine environment is shared between twins, and so any contributions from that shared environment will not be disentangled in your proposed model.