Cut from the same cloth
So, part of my dream last night involved these aliens who reproduced by making this special material and cutting hexagons from it, and these hexagons would become new individuals. After being cut free the individuals would be subjected to a screening process which judged them on their geometry and the purity of the material they were cut from. Individuals who fail this test generally suffer mental problems, although outside observers are unsure if it's because of their substandard shape and/or makup or if it's because of the trauma of being declared substandard.