Biological evolution is fundamentally a nonequilibrium process, as
described by the tree of life on large time scales.  In this talk, we
discuss how the irreversibility of evolution is generated at the molecular
level, and how it can be detected by today's genomics. A key role in this
process is played by gene interactions, which build up temporal
correlations between mutations. As an example, we discuss irreversibility
in the evolution of influenza, or why last year's vaccine is no good for
the next flu.