The fact that the cosmic abundances of baryonic and dark matter are so similar, despite their very different astrophysical behavior, is taken as a serious hint from Nature. We propose a rich dark sector parallel in structure to that of the standard model, and related to it via a ℤ₂ exchange symmetry. A WIMP baryogenesis mechanism is mirrored in the dark sector; small breakings in the ℤ₂symmetry result in the dark matter being made of dark neutrons, which are the lightest dark baryons. An extra-dimensional realization of our model in the far UV naturally explains the hierarchical couplings of both sectors as well as the requisite ℤ₂-breakings. We carefully trace the cosmic history of both sectors, paying particular attention to serious pitfalls inadequately considered in previous literature, such as light relics and dark big bang nucleosynthesis. Finally, we briefly discuss potential experimental signatures.