Dependence of QCD hadron masses on the number of dynamical quarks

We have studied the hadron spectrum while varying the number of light dynamical quarks when the physical lattice spacing and volume are held fixed relative to the rho mass. For two and zero flavors of staggered fermions, we find the nucleon to rho mass ratios (extrapolated to zero valence quark mass) are very similar. However, for four flavors the ratio is 7% (2 standard deviations) above the two flavor result.