Previously we showed that mouse stocks derived from wild-caught progenitors are long-lived relative to genetically heterogeneous mice derived from laboratory-adapted strains. Here we replicate this life-span effect, and show that F2 hybrids between wild-derived and laboratory-derived stocks have intermediate survival patterns. Moreover, wild-derived mice are small, lean, and slow to mature, and have low serum insulin-like growth factor-I (IGF-I) relative to genetically heterogeneous mice. These traits, too, were at intermediate levels in the F2 hybrids. Furthermore, serum IGF-I at 6 months was a significant predictor of life span in two different populations of F2 hybrid mice. Pooling across stocks, life span was negatively correlated with body weight and serum IGF-I levels, and positively correlated with age at vaginal patency and serum leptin levels. Overall, these finding suggest that wild-derived mice harbor alleles that increase longevity, perhaps through effects on growth, maturation, and early-life hormone levels.