To ensure safety and ease toileting while parents work in the fields, mothers in rural northeastern China place infants on their backs in bags of sand (similar to kitty litter) for most of the day, continuing this practice into the second year. Compared with diapered infants in the same region, sandbag-reared babies are greatly delayed in sitting and walking. Among the Zinacanteco Indians of southern Mexico and the Gusii of Kenya, adults view babies who walk before they know enough to keep away from cooking fires and weaving looms as dangerous to themselves and disruptive to others. As a result, Zinacanteco and Gusii parents actively discourage infants' gross-motor progress. In contrast, among the Kipsigis of Kenya and the West Indians of Jamaica, babies hold their heads up, sit alone, and walk considerably earlier than North American infants. In both societies, parents emphasize early motor maturity, practicing formal exercises to stimulate particular skills. In the first few months, babies are seated in holes dug in the ground, with rolled blankets to keep them upright. Walking is promoted by frequently bouncing infants on their feet. As parents in these cultures support babies in upright postures and rarely put them down on the floor, their infants usually skip crawling-a motor skill regarded as crucial in Western nations! Finally, the current Western practice of having babies sleep on their backs delays gross-motor milestones of rolling, sitting, and crawling. Regularly exposing infants to the tummy-lying position during waking hours prevents these delays.