Cirrus@Austlit

'Sue Isle’s "Sisterchild" is about Simeon and Leah, Siamese twins born into a post-apocalyptic Australian tribe. Leah is nothing more than a torso and head sprouting from Simeon’s waist, and their tribe decides Leah has to be cut out so that her brother can enter manhood as a properly formed male. Although this is a death sentence for his sister, Simeon is tempted at first, but at Leah’s urgings and overwhelmed by guilt, he flees into the desert. Picked up by a trio of men who wander the desert in a Sherman tank (I kid you not), who are shocked but not offended by Leah, they are taken to a town where the technology exists that can safely separate them.'

Source: Eidolon (http://eidolon.net/?review=shortfiction5&pagetitle=Short+Fiction+Reviews+5).