greater no. of chromosomes may or may not mean greater genetic variation, and the variation at a particular locus is also required in the population…And the availibility of raw material is an important point, so the rate of change of gene frequencies in the adaptive landscape also depends upon the viability of the variants possible, so even if alot’f mutants are available , and their viability is very less, then there won’t be gene frequency change to major extent, i.r. in ur words more rate/incidence of evolution…