Traditionally, Inuit children were breast-fed for three to five years and sometimes into the sixth and seventh years. Prolonged breast-feeding was practiced by many precontact hunting and gathering populations to ensure the survival of offspring. Recent research has shown that prolonged breastfeeding inhibits ovulation, making for longer intervals between children. With the introduction to the Arctic of bottle-feeding in the late 1950s and early 1960s, the traditional strategy of birth control and birth spacing was disrupted. This, in turn, led to an increase in live births, resulting in a significant shortening of birth intervals.