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We use a particular machine learning approach, called the genetic algorithms (GA), in order to place constraints on deviations from general relativity (GR) via a possible evolution of Newton's constant $μ\equiv G_\mathrm{eff}/G_\mathrm{N}$ and of the dark energy anisotropic stress $η$, both defined to be equal to one in GR. Specifically, we use a plethora of background and linear-order perturbations data, such as type Ia supernovae, baryon acoustic oscillations, cosmic chronometers, redshift space distortions and $E_g$ data. We find that although the GA is affected by the lower quality of the currently available data, especially from the $E_g$ data, the reconstruction of Newton's constant is consistent with a constant value within the errors. On the other hand, the anisotropic stress deviates strongly from unity due to the sparsity and the systematics of the $E_g$ data. Finally, we also create synthetic data based on a next-generation survey and forecast the limits of any possible detection of deviations from GR. In particular, we use two fiducial models: one based on the cosmological constant $Λ$CDM model and another on a model with an evolving Newton's constant, dubbed $μ$CDM. We find that the GA reconstructions of $μ(z)$ and $η(z)$ can be constrained to within a few percent of the fiducial models and in the case of the $μ$CDM mocks, they can also provide a strong detection of several $σ$s, thus demonstrating the utility of the GA reconstruction approach.