A firm link between small size at birth and later more centralized fat patterning has been established in previous research. Relationships between shortened interbirth intervals and small size at birth suggest that maternal energetic prioritization may be an important, but unexplored determinant of offspring fat patterning. Potential adaptive advantages to centralized fat storage (Baker et al., 2008: In: Trevathan W, McKenna J, Smith EO, editors. Evolutionary Medicine and Health: New Perspectives. New York: Oxford) suggest that relationships with interbirth intervals may reflect adaptive responses to variation in patterns of maternal reproductive effort. Kuzawa (2005: Am J Hum Biol 17:5–21; 2008: In: Trevathan W, McKenna J, Smith EO, editors. Evolutionary Medicine and Health: New Perspectives. New York: Oxford) has argued that maternal mediation of the energetic quality of the environment is a necessary component of developmental plasticity models invoking predictive adaptive responses (Gluckman and Hanson 2004: Trends Endocrinol Metab 15:183–187). This study tested the general hypothesis that shortened interbirth intervals would predict more centralized fat patterning in offspring. If long-term maternally mediated signals are important determinants of offspring responses, then we expected to observe a relationship between the average interbirth interval of mothers and offspring adiposity, with no relationship with the preceding interval. Such a finding would suggest that maternal, endogenous resource allocation decisions are related to offspring physiology in a manner consistent with Kuzawa's description. We observed exactly such a relationship among the Ache of Paraguay, suggesting that maternally mediated in utero signals of postnatal environments may be important determinants of later physiology. The implications of these findings are reviewed in light of life history and developmental plasticity theories and ourability to generalize the results to other populations. Recommendations for further empirical research are briefly summarized. Am. J. Hum. Biol., 2009. © 2008 Wiley-Liss, Inc.