Jeffrey Langley

Boundaries in biology are complex, extending across levels, time and space in gradient, varied and discordant ways.1 Which elements of those boundaries are relevant to individuation is sensitive to the biological features of those systems and our research questions; no one element sets the boundary against which others deviate. In practice, biologists accommodate this by adopting a levels-of-resolution approach to boundary drawing rather than employing categorical criteria of individuation. This feature of lineage divergence, diversification and interaction is especially prominent for lineage-generating processes such as reproduction. And though heuristic idealisation can be a useful strategy in the face of complexity, conflating this with metaphysical claims is a mistake. Human pregnancy is a process of lineage generation. Our metaphysical accounts of pregnancy and lineages, then, should align. To evaluate how the metaphysics of pregnancy affects debates in reproductive ethics, Arjun Devanesan2 follows the literature and starts with the metaphysical assumption of classical mereology (but see Meincke3). Yet, this is ill-suited for providing a robust metaphysics of lineage generation and divergence, for example, the defining axioms of parthood relations in classical mereology conflict with biological parthood.4,i Instead, biologists studying lineages have largely …