“…Gautier and Henry, 1958). Indeed, it was historical demographic research that focused attention on postpartum amenorrhea and on lactation effects as explanations for differences in fertility within and between populations (Fildes, 1986(Fildes, ,1988(Fildes, ,1995Henry, 1961;McLaren, 1979). Subsequent studies have confirmed a strong association between the duration of breast-feeding and the length of birth intervals, as well as support for the contraceptive effects of lactation (Dettwyler, 1987(Dettwyler, , 1988(Dettwyler, , 1995aGoldman et al, 1987;Knauer, 1985;Konner, 1985;McNeilly et al, 1983;Short, 1993;Stuart-Macadam and Dettwyler, 1995).…”