Biological Individuality and Fallacies of Composition

Within the philosophy of biology, there is widespread acceptance of pluralism about biological individuality, according to which there are (at least) two theoretically important but distinct properties with a claim to the label ‘biological individuality’: evolutionary individuality and physiological individuality. Many who accept this also commit themselves—sometimes explicitly, often implicitly—to the further, surprising claim that the evolutionary individual and the physiological individual corresponding to a seemingly singular multicellular organism, such as a human being, are in fact distinct. I raise some problems for this distinctness claim, before developing a way of holding onto pluralism while rejecting this supposed consequence of it. I do so by uncovering some natural but hidden assumptions concerning the connections between certain evolutionarily significant properties of multicellular organisms and certain properties of their parts—assumptions which, once made explicit, can be seen to amount to fallacies of composition. I show that, by rejecting these assumptions, philosophers of biology can hold on to the appealing idea that familiar multicellular organisms are at once both evolutionary and physiological individuals.