  Basing our arguments on the theory of active liquid crystals, we demonstrate
both analytically and numerically, that the activity can induce an effective
free energy which enhances ordering in extensile systems of active rods and in
contractile suspensions of active discs. We argue that this occurs because any
ordering fluctuation is enhanced by the flow field it produces. A phase-diagram
in the temperature-activity plane compares ordering due to a thermodynamic free
energy to that resulting from the activity. We also demonstrate that activity
can drive variations in concentration, but for a different physical reason that
relies on the separation of hydrodynamic and diffusive timescales.
