Nursing frequency and birth spacing in Kung hunter-gatherers
Konner, M.
Ippf Medical Bulletin 15(2): 1-3
1978
ISSN/ISBN: 0019-0357 PMID: 12278620 Document Number: 129591
In a study on infant growth and development among the ]Kung San, hunter-gatherers of northwestern Botswana in 1969-71, a pattern of nursing was observed that was striking. Age at weaning was typically later than 3 years; all infants under a year of age in the population were nursing, as were 90% of those in the second year, and 75% of those in the third year. Child under 3 awoke to nurse 1 or more times in the night. Nursing in the day was frequent and brief. At all ages under 2 years, fewer than 25% of 15 minute observations of the mother-infant pair elapsed without a nursing session. The ]Kung population has unusually long birth spacing, as high as 44 months in traditional bands, resulting in an overall low natural fertility of 4.7 live births per woman. Extensive experimental and clinical literature shows that prolactin is promptly secreted in response to nipple stimulation in human females, increasing 2 to 20 fold in plasma during 5 to 15 minutes of mechanical stimulation, with a half-life in plasma of 10 to 30 minutes. Prolactin suppresses gonadal function, either directly at the ovary or indirectly through gonadotropin antagonism at the anterior pituitary. When the child is between 2 and 3 years old, the level of prolactin, which presumably had been tonically high previously, is allowed to fall low enough for a long enough time so that its antigonadal or antigonadotrophic effects are impaired, and ovarian cycling is reinstated.