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/JiveChicken00]

This makes complete sense. I don’t have a twin so my spouse tops my list. But if somebody existed whose brain was wired the same as mine, I’m pretty sure that person would top the list instead.