Dark energy and dark matter are still poorly understood today. Indeed, it has never been shown even that the two are in fact two separate substances. Unified dark matter models work under the assumption that they are in fact not separate, where a single perfect fluid known as quartessence plays the part of both dark matter and dark energy.

  Here we review the present status of UDM (in particular of the Chaplygin gas) covering their problems and argue that for the first time evidence showing dark energy and dark matter to be of different natures was found.