The topography of ocean ridges and rifts show a distinct asymmetry. The eastern sides of the East Pacific Rise, the Mid-Atlantic Ridge, and the NW Indian Ridge are, on average, 100--300 m more elevated than the conjugate flank to the west. The asymmetry is maintained when bathymetry is plotted versus the square root of crustal age. A comparable topographic asymmetry occurs in the Red Sea and Baikal rifts where the eastern continental shoulders are more elevated. We suggest that depleted and lighter asthenosphere generated below the ocean ridge was shifted eastward relative to the lithosphere, determining a density deficit below the eastern flank. The eastward migration of the lighter Atlantic asthenosphere below the African continent could eventually have contributed to the anomalous postrift uplift of Africa. This model suggests that the westward drift of the lithosphere relative to the underlying mantle might be a global phenomenon.