which became unbearable for him. Hallam interrupted immunosuppressive
treatment, organ rejection started, and eventually he asked that his hand be
amputated (Dubernard et al. 2001). With face transplants (36 patients under-
went face transplants from 2006 to 2016 (Siemionow 2016)), recipients and
doctors are confronted with even more difficult and pressing identity issues
(Carosella and Pradeu 2006).
These are certainly extreme cases. Nonetheless, every year in the United
States approximately 16,000 kidney and almost 6,000 liver transplantations are
done (Wolfe et al. 2010), and in the European Union around 19,000 kidney and
7,000 liver transplants (European Directorate for the Quality of Medicines &
HealthCare 2015). Despite the apparently routine nature of such transplanta-
tions, the body does not seem ready to tolerate any component coming from
another organism. First, in the case of the kidney, for example, medical doctors,
before proceeding to transplantation, carefully check compatibility between
donor and recipient, particularly in terms of the major histocompatibility com-
plex (MHC) (Kahan 2003). Second, the transplant patient receives immuno-
suppressive drugs. Thus, even if not all these transplantations prompt the kind of
identity crisis experienced by Clint Hallam, they do raise the questions of how
the boundaries of a biological individual are defined and under which conditions
some external elements can become part of that biological individual. These are
exactly the questions that led the nascentfield of immunology, in thefirst half of
the twentieth century, to take on the problem of biological individuality via
a combination of reflections about transplantation and infectious diseases.
The aim of this section is to show why immunology makes a critical con-
tribution to the problem of biological individuality, especially from the points of
view of boundaries and parthood just mentioned. Immunology has raised this
problem mainly through the concepts of“self”and“nonself,”so much so that in
the 1980s immunology was famously named“the science of self-nonself dis-
crimination”(Klein 1982). I examine here the conceptual and experimental
limitations of the self–nonself framework, while insisting that this critique does
not undermine the essential claim that immunology plays a key role in the
definition of biological individuality.
The outline of the section is as follows. First, I describe the birth of the self–
nonself framework in immunology. I then spell out how current immunologists
conceive biological individuality, especially on the basis of recent research on
autoimmunity, immunological tolerance, and symbiosis. Third, I explore three
arguments demonstrating the central contribution of immunology to biological
individuality. Fourth, I show that the functioning of the immune system sheds
light on how a set of heterogeneous constituents can be turned into an integrated
14 Elements in the Philosophy of Biology