Human life history is unique in the great length of its juvenile, or immature, period. This lengthened period(1) is often attributed to the time required for youth to master the culture, particularly subsistence and survival skills. But studies in increasing number show that children become skilled well before they gain complete independence and adult status. As children learn through play and participation in the domestic economy, they seem to be acquiring a reserve capacity of skills and knowledge that may not be fully employed for many years. To resolve this paradox, the theory offered here poses that this reserve capacity of children, both individually and collectively, can be rapidly activated to offset a shortfall in familial resources brought on by crises such as the loss of older family members. Additionally, social forces engendered by war, disease, famine, and economic change may lead to the wholesale recruitment of children into the labor forcewith consequent attenuation of the developmental opportunities of an extended juvenility. In effect, humans display a primary life history strategy and an accelerated strategy with a shortened period of dependency. A wide array of cases from anthropology and history will be offered in support of this proposal.