  A recent article in Nature Physics unified key results from thermodynamics,
statistics, and information theory. The unification arose from a general
equation for the rate of change in the information content of a system. The
general equation describes the change in the moments of an observable quantity
over a probability distribution. One term in the equation describes the change
in the probability distribution. The other term describes the change in the
observable values for a given state. We show the equivalence of this general
equation for moment dynamics with the widely known Price equation from
evolutionary theory, named after George Price. We introduce the Price equation
from its biological roots, review a mathematically abstract form of the
equation, and discuss the potential for this equation to unify diverse
mathematical theories from different disciplines. The new work in Nature
Physics and many applications in biology show that this equation also provides
the basis for deriving many novel theoretical results within each discipline.
