The sheer expanse of the Universe and the dimming of sources with distance presents a significant problem for understanding galaxy evolution, with the received emission from increasingly distant objects weakening to the point where they are no longer detectable. While the Square Kilometre Array pathfinder telescopes in Australia and South Africa will vastly increase our ability to directly detect distant emission from neutral atomic hydrogen, these telescopes will still have limits as to the mass and distance of galaxies they can study. New methods, involving the statistical combination of the signals from many different galaxies together, can provide a powerful new window through which to advance the observational exploration of the Universe, giving us crucial information on how the average properties of galaxies have changed with time. This project will utilise early science data from the Square Kilometre Array pathfinders, in combination with that from existing facilities, to refine our use of these statistical analysis methods (HI stacking, intensity mapping) and extend distance range over which we can use spectral line observations to understand galaxy evolution. Numerous projects exist in this space including studies of the cosmic evolution of gas, galaxy dynamics, and galaxy scaling relations.