  We trace the development of elliptic anisotropy (v2) via parton-parton
collision history in two transport models. The parton v2 is studied as a
function of the number of collisions of each parton in Au+Au and d+Au
collisions at sNN =200 GeV. It is found that the majority of v2 comes from the
anisotropic escape probability of partons, with no fundamental difference at
low and high transverse momenta. The contribution to v2 from hydrodynamic-type
collective flow is found to be small. Only when the parton-parton cross-section
is set unrealistically large does this contribution start to take over. Our
findings challenge the current paradigm emerged from hydrodynamic comparisons
to anisotropy data.
