[1maginary]

They controlled for that by having about as many fraternal twins in this study, though.

It's particularly surprising to me that they got very similar results with regards to discrepancy between fraternal and identical twins when testing again at a later age.

[jasonkostempski]

I don't get how that could be a control against assuming genetic causation. Fraternal twins still have similar genetics, right?

[klodolph]

Fraternal twins and identical twins both have the same environment growing up, they experience the same hormones at the same time during gestation, they live in the same city, sleep in the same bed. They eat the same foods at the same times of day and in the same amounts, excepting personal preference. However, fraternal twins share 50% of their genes (on average) and identical twins share near 100%.

[mitchellshow]

Yes, and in order to state "this is definitely a genetic cause" you would need to rule out other factors. Including fraternal twins is interesting, but unless they were separated at birth (and not even then really) this could just as easily read "How Kids See the World Depends a Lot on How They Were Raised" which is a pretty obvious conclusion to draw and not particularly headline worthy.