  Measurements of galaxy clustering in upcoming surveys such as those planned
for the Euclid and Roman satellites, and the SKA Observatory, will be sensitive
to distortions from lensing magnification and Doppler effects, beyond the
standard redshift-space distortions. The amplitude of these contributions
depends sensitively on magnification bias and evolution bias in the galaxy
number density. Magnification bias quantifies the change in the observed number
of galaxies gained or lost by lensing magnification, while evolution bias
quantifies the physical change in the galaxy number density relative to the
conserved case. These biases are given by derivatives of the number density,
and consequently are very sensitive to the form of the luminosity function. We
give a careful derivation of the magnification and evolution biases, clarifying
a number of results in the literature. We then examine the biases for a variety
of surveys, encompassing galaxy surveys and line intensity mapping at radio and
optical/near-infrared wavelengths.
