  Helioseismology can provide strong constraints on the evolution of Newton's
constant over cosmic time. We make use of the best possible estimate of 8640
days of low-$\ell$ BISON data, corrected for the solar cycle variation, to
obtain a new constraint on an evolving gravitational constant. In particular,
by means of a Bayesian analysis we conclude that ${{\dot{G}/G}_{\rm
today}}=(1.25\pm 0.30) \times 10^{-13} \; \mathrm{yr}^{-1}$. Our result, a
4-$\sigma$ effect, is more than one order of magnitude stronger than previous
constraints obtained with helioseismology. We also take into account possible
systematic effects by considering the theoretical uncertainties on the
efficiency of the proton-proton $(pp)$ fusion cross-section. We show that
models with variable $G$ significantly outclass models with no secular
variation of $G$, viz by a Bayes factor exceeding 30.
