Microchimerism is, by definition, the survival and proliferation of genetically "non-self" cells in an organism. When these cells are found spontaneously in a woman, their source is most often presumed to be fetal. As one microchimerism researcher says, "the fetus essentially is a foreign antibody, or antigen, whatever you want to call it. It's a foreign thing that's... you've got to consider it an organ transplant." In the past ten years, attempts to explain "naturally occurring" microchimerism have rendered it unfathomable, and then pathological, and then biologically advantageous. All the while, report upon report confirms that "male" cells can be found in women: in numbers small and large, in many kinds of tissue, in disease and wellness, in mothers and in the childless. Those closest to the phenomenon, a handful of persistent researchers from varied disciplines, speculate constantly about the provenance and role of these "foreign" cells. The language that they inherit from centuries of Western political philosophy - and most directly from microchimerism's artificial sister, organ transplantation - upholds an order of discrete and traceable individuals commonly understood as "self" and "non-self." I argue here that this language and formulation was "good enough" for framing material findings as long as the phenomenon was rare and confined to particular marked bodies, but that its utility has run out. Microchimerism could once be understood as "matter out of place" and interesting for medical and lay audiences alike precisely because of its unnatural, or even supernatural, status (both of which are in keeping with the mythical genealogy of its referent, the Chimaera). But a threshold is crossed if we are all intercorporeal at a cellular level. Meanwhile, microchimerism researchers are beholden to inadequate categories - self/other, male/female, cell/person, natural/made - even as they are daily proving the material inadequacy of these biosocial categories.
Aryn Martin is Associate Professor at York University, Toronto, teaching in both Sociology and Science and Technology Studies. Her research and writing concerns social and historical studies of biomedicine, as well as feminist theory. In work that appears in Social Studies of Science, Osiris, Social Problems, Body & Society and elsewhere, Aryn has written about genetic chimaeras, maternal-fetal microchimerism, immunology and pregnancy as phenomena that trouble biological and political notions of the individual.