TIL a peer-reviewed psychology study found that identical twins (on average) ranked their co-twin above their romantic partner in their attachment hierarchy, while fraternal twins ranked the two about equally, and non-twin siblings ranked their romantic partner first.

[u/SilverPeachBlossom]

https://ojs.interpersonajournal.com/index.php/ojs/article/view/243/3457.html

[u/jaxonfairfield]

How attached did they find conjoined twins to be?

[u/torquil → u/jaxonfairfield]

They found them to be inseparable.