But we cannot content ourselves with old narratives just because they are comfortable and familiar. Theoretical epidemiologist Sunetra Gupta presents the case that many infectious diseases, including influenza virus, evolve by the reassembly of old parts from disparate sources, not by a continuous evolutionary stroll somewhere new. Rather than a Blind Watchmaker tinkering with last year’s model – Richard Dawkins’ famous image of evolution – a Mad Scientist assembles new Frankensteins each year in his laboratory.

Certainly, the new flu vaccine you get each year does not sound like a link in a continuous chain; it’s more like a mixture of A/New Caledonia/20/99 and B/Shandong/7/97, blended from past disease strains. Gupta and her group at Oxford contrast the cozy classical notion of antigenic drift with antigenic thrift, which conjures the apposite image of rooting around in a charity shop to find old clothes to make a new outfit.

Which view of the evolution of the influenza virus is correct is currently the subject of active and contentious scientific study.

The point is that metaphors have great power in science. They’re not forced on us by reality, though.