  We study the effect of the dynamical friction induced by the presence of
substructure on the statistics of the collapse of density peaks. Applying the
results of a former paper we show that within high density environments, like
rich clusters of galaxies, the collapse of smaller peaks is strongly delayed
until very late epochs. A bias of dynamical nature thus naturally arises
because high density peaks preferentially collapse For a standard CDM model we
find that this dynamical bias can account for a substantial part of the total
bias required by observations on cluster scales.
