Stranger than glue

Experiment indicates that quarks carry only a small fraction of the proton's spin and that the strange quark sea in the proton is substantially polarized. An alternative explanation requires a large polarization of gluons in the proton. This explanation is strongly constrained by the existing experimental data and by a recent lattice calculation. The surprisingly small contribution of quarks to the proton spin requires a stranger explanation than anomalous gluons.