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The density profile of simulated dark matter structures is fairlywell-established, and several explanations for its characteristics have beenput forward. In contrast, the radial variation of the velocity anisotropy hasstill not been explained. We suggest a very simple origin, based on the shapesof the velocity distributions functions, which are shown to differ between theradial and tangential directions. This allows us to derive a radial variationof the anisotropy profile which is in good agreement with both simulations andobservations. One of the consequences of this suggestion is that the velocityanisotropy is entirely determined once the density profile is known. Wedemonstrate how this explains the origin of the \gamma-\beta relation, which isthe connection between the slope of the density profile and the velocityanisotropy. These findings provide us with a powerful tool, which allows us toclose the Jeans equations.

Might we eventually understand the origin of the dark matter velocity anisotropy?