We simulate adaptive radiations of a single clade in a spatially explicit environment. We investigate the geographical overlap of lineages during and after evolutionary branching (speciation). The spatial overlap at speciation varied continuously from complete ("sympatry") to none ("allopatry") depending on the ecological circumstances (local and regional environmental heterogeneity, dispersal rate, and species richness in the communities). The frequency distribution of the geographical overlap at speciation was strongly bimodal regardless of ecological circumstance. The mean overlap, however, varied considerably during the course of a single radiation, in some cases with a consistent negative trend. The relationship between mean geographical overlap of sister species and time since speciation was surprisingly flat, i.e., old sister species tended to have roughly the same overlap as young ones. However, if local heterogeneity was relatively low (few local niches) and dispersal rate high, then the mean overlap increased with time since speciation. Post-speciation range shifts and the changes in geographical overlap at speciation with time during the cladogenesis lead us to the conclusion that the relationship between current sister species overlap and time since speciation is of limited use for inferring the mode of speciation.