  This paper investigates whether nonlinear gravitational instability can
account for the clustering of galaxies on large and small scales, and for the
evolution of clustering with epoch. No CDM-like spectrum is consistent with the
shape of the observed nonlinear spectrum. Unbiased low-density models greatly
overpredict the small-scale correlations; high-density models would require a
bias which does not vary monotonically with scale. The true linear power
spectrum contains a primordial feature at $k\simeq 0.1 \hompc$, and must break
quite abruptly to an effective slope of $n\ls -2.3$ on smaller scales This
empirical fluctuation spectrum also fits the CFRS data on the evolution of
clustering, provided the universe is open with $\Omega\simeq 0.3$. Only this
case explains naturally how the small-scale spectrum can evolve at the observed
rate while retaining the same power-law index. An unbiased open model also
matches correctly the large-scale COBE data, and offers an attractively simple
picture for the phenomenology of galaxy clustering.
