  The traditional view of the morphology-spin connection is being challenged by
recent integral-field-unit observations, as the majority of early-type galaxies
are found to have a rotational component that is often as large as a dispersion
component. Mergers are often suspected to be critical in galaxy spin evolution,
yet the details of their roles are still unclear. We present the first results
on the spin evolution of galaxies in cluster environments through a
cosmological hydrodynamic simulation. Galaxies spin down globally with cosmic
evolution. Major (mass ratios > 1/4) and minor (1/4 $\geq$ mass ratios > 1/50)
mergers are important contributors to the spin down in particular in massive
galaxies. Minor mergers appear to have stronger cumulative effects than major
mergers. Surprisingly, the dominant driver of galaxy spin down seems to be
environmental effects rather than mergers. However, since multiple processes
act in combination, it is difficult to separate their individual roles. We
briefly discuss the caveats and future studies that are called for.
