  Measurements of galaxy clustering are now becoming possible over a range of
redshifts out to z=3. We use a semi-analytic model of galaxy formation to
compute the expected evolution of the galaxy correlation function with
redshift. We illustrate how the degree of clustering evolution is sensitive to
the details of the sample selection. For a fixed apparent magnitude limit,
galaxies selected at higher redshifts are located in progressively rarer dark
matter haloes, compared with the general population of galaxies in place at
each redshift. As a result these galaxies are highly biased tracers of the
underlying dark matter distribution and exhibit stronger clustering than the
dark matter. In general, the correlation length measured in comoving units,
decreases at first with increasing redshift, before increasing again at higher
redshift. We show that the epsilon-model often used to interpret the angular
correlation function of faint galaxies gives an inadequate description of the
evolution of clustering, and offers no physical insight into the clustering
process. We compare our predictions with those of a simple, popular model in
which a one-to-one correspondence between galaxies and dark halos is assumed.
Qualitatively, this model reproduces the correct evolutionary behaviour at high
redshift, but the quantitative results can be significantly in error. Our
theoretical expectations are in good agreement with the high redshift
clustering data of Carlberg etal and Postman etal but are higher than the
measurements of Le Fevre etal.
