Mammalian aging results from a replicative decline in the function of somatic stem cells and other self-renewing cells. Recent studies (Monzen et al., 2008; Nishino et al., 2008; Sanna et al., 2008; Weedon et al., 2008) link a chromatin-associated protein, HMGA2, to development, height, and mouse stem cell aging during late fetal development and young adulthood.