 For one thing, while the more ‘macroscopic’ a system, the more pervasive the effects of decoherence and the more complex the structures that emerge through it, this is only a rule of thumb. Not all molecules are chiral (bound ammonia groups tend to be in superpositions for instance), and there is no clear-cut criterion for when a system should count as macroscopic. Indeed, even apart from examples like superconducting systems, there might be surprising cases in which not all interference effects have been suppressed by decoherence even at the macroscopic level. A famous proposal by Hameroff and Penrose (1996) links the phenomenon of consciousness with the possibility of quantum superpositions within microtubules (and their subsequent active suppression via collapse); other authors interpret the mathematically quantum-like effects described within ‘quantum cognition’ as actual quantum effects (for both, see the entry on  quantum approaches to consciousness).  At present, most macroscopic quantum effects remain speculative at best, but plausible cases for the continuing relevance of quantum superpositions at the macroscopic level can be found in quantum biology, notably the studies of possible quantum effects in the navigational system of migrating birds (Cai, Guerreschi and Briegel 2010).