Regulation of nursing in chimpanzees.

The regulation of nursing was studied in captive chimpanzees from birth to 6 months of age. It was asked whether regulation was predictable or timing was irregular. A search for unimodal frequency distributions resulted in a distinction among nursing bouts, nursing episodes (bouts with brief interruptions) and nursing pauses. The frequency distributions of these types were either normal with very large standard deviations or exponential (i.e., randomly terminated). This implies a very irregular timing. Longer nursing episodes were followed by somewhat longer pauses; pauses with daytime sleep (that were relatively long) were followed by longer nursing. However, these regulatory effects were only slight. Most of this loose regulation of nursing was due to the infant, as the mothers did not put the infant on the breast and usually were permissive. Comparisons with humans suggest a similarly loose organization as well as frequent feeding in societies that provide relatively unlimited access to the breast. The regular 4-hr, meal-like schedule in industrial countries seems mainly to be due to human mothers and their advisors.