The role of pre-mastication in the evolution of complementary feeding strategies: a bio-cultural analysis
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Human milk is a poor source of iron. At birth, the newborn is well endowed with iron stores, which are adequate to meet his/her needs for the first 4-6 months of infancy (WHO March 2001), and iron deficiency is rare. On the other hand, iron deficiency is prevalent among infants between 6- 12 months of age, particularly in developing countries, and iron supplementation during breastfeeding, and thereafter, is recommended, in addition to 6 months exclusive breastfeeding (WHO, 2002). If exclusively breastfed infants are becoming anemic by the time complementary foods are first being introduced, this raises a challenge to our assumptions about the nature of human bio-cultural evolution. Is the anemia of infancy normal or did usual feeding practices prevent it? As iron supplementation was not possible until recently, I hypothesized that exclusive breastfeeding was complemented by premasticated foods during our evolution as a hunting-gathering species. In other words, that iron deficiency in infancy is a recent problem in human society, which was previously prevented by premastication. The goals of this research were to assess the prevalence of premastication in non-modern societies in order to determine whether (1) it was prevalent enough to support plausibly its role as a behavioral adaptation to prevent iron deficiency and (2) to determine whether the potentially detrimental effects of premasticated food were harmful enough to be selected against. This research involves several lines of investigation: 1) bringing together the evidence that iron deficiency is a common problem, which is now found in many different regions of the world, 2) a cross-cultural study, using the Human Relations Area Files (HRAF) to obtain ethnographic data on the distribution and time depth of premastication in human societies, 3) a field research study in China, based on interviews conducted by University students, to examine the potential for serious under-reporting of pre-mastication in the ethnographic studies, 4) a review of the iron content of foods that are reported to be premasticated, and 5) a review of the scientific literature on the content of saliva. In the HRAF analysis, 39 cultures out of 119 cultures (33%) that contain any information on infant feeding describe premastication as an infant feeding practice. Notably none of the ethnographies from China mention premastication. However, the field survey in China, with a sample of 104 elite college students, found that 63% (65 of 104) were fed pre-masticated food when they were infants, and those who received premasticated foods were more likely to be fed complementary foods earlier than those who did not. The survey findings support the notion that premastication tends to be under-reported in ethnographic studies. Although salvia has not been as extensively studied as breastmilk, the review of the biomedical literature suggests that it contains several potential positive substances from the perspective of infant health and fewer negative substances than are commonly assumed. The results of the various lines of investigation suggest that pre-mastication has been a common practice in human societies, but has been significantly under-reported. The potential dangers of increased infection that pre-mastication poses for infant health have probably been less serious than the disadvantages of not engaging in pre-mastication, which is a means of giving infants iron to prevent deficiency as stores begin to drop during the first semester of life. Therefore I conclude it is probable that pre-mastication was the behavior/cultural solution to the complementary feeding challenge in human societies, that it probably prevented the level of iron deficiency, which is common today in poor societies.
dissertation or thesis