  Hierarchical gravitational clustering creates galaxies that usually do not
fully share the dynamical history of an average particle in the mass field. In
particular, galaxy tracers identified in numerical simulations can have
individual velocity dispersions in virialized regions a factor \bvs\ lower than
the dark matter. The field average of the pairwise velocity dispersion depends
on the statistical weighting of collapsed regions, so that the tracer pairwise
dispersion is a different factor, \bvp, times the density field value. A model
of a cool equilibrium tracer population demonstrates that mass to light
segregation is very sensitive to single particle velocity bias. For the
$\phi=-GM/(r+a)$ potential a $\bvs=0.9$ tracer indicates a virial mass about a
factor of 5 low. The likely value of \bvs\ is estimated and the simple
equilibrium model is tested for applicability using a $10^6$ particle
simulation of the formation of a single cluster from cosmological initial
conditions. From this simulation, the value of \bvs\ is estimated as
$0.8\pm0.1$. The pairwise velocity dispersion bias, \bvp, which is equal to
\bvs\ augmented with any anti-bias of galaxies against high velocity dispersion
clusters. The value of \bvp\ is estimated to be 15\% less than \bvs,
consequently $\bvp=0.6^{+0.2}_{-0.1}$. Comparison of cluster mass and
luminosity profiles at large radii is a test for the existence of single
particle velocity bias. [compressed postscript file cluster.ps.Z via anonymous
ftp from orca.astro.washington.edu in ~ftp/pub/hpcc, or
<EMAIL_ADDRESS>