Numerical studies of the plane symmetric, vacuum Gowdy universe on T(3
)xR yield strong support for the conjectured asymptotically velocity t
erm dominated (AVTD) behavior of its evolution toward the singularity
except, perhaps, at isolated spatial points. A generic solution is cha
racterized by spiky features and apparent ''discontinuities'' in the w
ave amplitudes. It is shown that the nonlinear terms in the wave equat
ions drive the system generically to the ''small velocity'' AVTD regim
e and that the spiky features are caused by the absence of these terms
at isolated spatial points.