The difference between long and short GRB hosts is also apparent in the distribution of stellar populations in these galaxies.  Consistent with their exclusive origin in early-type galaxies, long-duration GRBs have populations of stars with typical ages of 60 Myr.  Short-duration GRBs have (on average) older stellar populations, in some cases extending out to several Gyr (Figure 17).  While such modeling typically assumes a single stellar population, it nonetheless reinforces the picture of short-duration GRB hosts as arising from an older stellar population.