Through optical and X-ray observations of clusters from z=0 to z=0.9, we have discovered that their member galaxies have been gradually falling to the cluster centers, presumably via drag force from the plasma, plus dynamical friction (Gu+13; Gu+16). This discovery suggests that the presence of hot plasmas significantly affects the dynamics and evolution of galaxies, and encourage future collaborations among optical, X-ray, and numerical studies.