  We present extensive new \textit{ab intio} path integral Monte Carlo results
for the momentum distribution function $n(\mathbf{k})$ of the uniform electron
gas (UEG) in the warm dense matter (WDM) regime over a broad range of densities
and temperatures. This allows us to study the nontrivial exchange--correlation
induced increase of low-momentum states around the Fermi temperature, and to
investigate its connection to the related lowering of the kinetic energy
compared to the ideal Fermi gas. In addition, we investigate the impact of
quantum statistics on both $n(\mathbf{k})$ and the off-diagonal density matrix
in coordinate space, and find that it cannot be neglected even in the strongly
coupled electron liquid regime. Our results were derived without any nodal
constraints, and thus constitute a benchmark for other methods and
approximations.
