Two exotic elements have been introduced into the standard cosmological model: non-baryonic dark matter and dark energy. The success in converting a hypothesis into a solid theory depends strongly on whether we are able to solve the problems in explaining observations with these dark elements and whether the solutions of these problems are unique within the standard paradigm without recourse to alternative scenarios. We have not achieved that success yet because of numerous inconsistencies, mainly on galactic scales, the non-detection so far of candidate particles for dark matter, and the existence of many alternative hypotheses that might substitute the standard picture to explain the cosmological observations. A review of some ideas and facts is given here.