What does this equation mean?

None of this derives Darwin from physics, and it does not need to. Natural selection is a logically separate claim — that heritable variation plus differential reproduction produces adaptation — that would remain true in a hypothetical universe with a different thermodynamic arrow, or none at all, provided that universe still somehow supported heredity. What the physics in this article supplies is the reason no such universe was ever going to get the chance: without a low-entropy past there is no preferred direction for anything to accumulate in; without decoherence and Landauer’s bound there is no such thing as a record that stays written; without fluctuation theorems there is no exact meaning to “forward is likelier than back” at the molecular scale where mutation actually happens; without England’s bound a replicator could not exist as a thermodynamic object at any cost; and without a real, measured photon gradient between a hot Sun and a cold sky there is no free energy for any of it to spend. The arrow of time is not a metaphor standing in for evolution’s engine. Measured in kelvin, in $k_{\mathrm B}$T $\ln$ 2 , and in the crossing point of two work distributions pulled from a single RNA hairpin, it is the engine’s fuel line.