   The question of how to define biological individuality is an ontological question about what individuals can evolve in response to natural selection. Many biological systems differ in form and in function from our garden variety Metazoans. How are we to understand the evolution of symbiotic communities involving bacteria with lateral gene transfer? How are we to make sense of the complex traits of eusocial insects? Not all these emergent individuals qua individuals replicate. Whether it’s by focusing on energy or persistence (or some other account) a complete understanding of fitness should reflect that fact—or accept that it cannot alone account for some adaptive change in the biological world.