This paper establishes the existence of a previously overlooked relationship between agglomeration and hours worked. Among non-professionals, hours worked decrease with the density of workers in the same occupation. Among professionals, a positive relationship is found. This relationship is twice as strong for the young as for the middle-aged. Moreover, young professional hours worked are shown to be especially sensitive to the presence of rivals. We show that these patterns are consistent with the selection of hard workers into cities and the high productivity of agglomerated labor. The behavior of young professionals is also consistent with the presence of keen rivalry in larger markets, a kind of urban rat race. This evidence of a rat race is nearly unique in the literature
