Mammals show a predictable scaling relationship between limb bone size and body mass. This relationship has a genetic basis which likely evolved via natural selection but it is unclear how much the genetic correlation between these traits in turn impacts their capacity to evolve independently. We selectively bred laboratory mice for increases in tibia length independent of body mass to test the hypothesis that a genetic correlation with body mass constrains evolutionary change in tibia length. Over 14 generations we produced mean tibia length increases of 11-12% while mean body mass was unchanged in selectively bred mice and random-bred controls. Using evolutionary scenarios with different selection and quantitative genetic parameters we also found that this genetic correlation impedes the rate of evolutionary change in both traits slowing increases in tibia length while preventing decreases in body mass despite the latter's negative effect on fitness. Overall results from this ongoing selection experiment suggest that parallel evolution of relatively longer hind limbs among rodents for example in the context of strong competition for resources and niche partitioning in heterogeneous environments may have occurred very rapidly on geological timescales in spite of the genetic correlation between tibia length and body mass.