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Yanomamo: Heterochronic Patterns


"There are three societies, accounting for 28 of the populations, which are coded in the Ethnographic Atlas as patrilocal or virilocal (the Yanomamo account for 26 populations). The average sex ratio in the junior age grade for these populations is 142 males per 100 females. Seven of the societies are coded in the Atlas as uxorilocal or neolocal, and the remaining case, the Guana, appear not to be patrilocal. These eight societies account for 20 populations with an average junior sex ratio of 103 males per 100 females. Thus while the warring societies as a whole have an average junior sex ratio of 126:100 it is the patrilocal component of the sample which produces the bias while the nonpatrilocal component shows a nearly even sex ratio. This correlation suggests that there are different cost/benefit ratios for raising daughters, given different residence arrangements. For this sample at least, nonpatrilocal systems do not support female infanticide. ... Divale (1974b) has shown a correlation between external warfare (in the absence of internal war) and matrilocality, and Harris has elsewhere emphasized this correlation (1977), noting also an association between matrilocal residence and a "diminution in preferential female infanticide" (1977:63). " (Hawkes, Kristen (1981) A third explanation for female infanticide. Human Ecology 9,1: pp. 83)

"Paternity probability appears to be very high among the Yanomamo, based on paternity exclusion tests conducted by my medical colleagues at the Department of Human Genetics, University of Michigan Medical School. Using several different antigen systems we tested blood saples from parent/offspring triads and, allowing for possible errors due to mislabeling specimens, estimated that the nonpaternity level is about ten percent." (Chagnon, N.A. (1979) Mate Competition, Favoring Close Kin, and Village Fissioning Among the Yanomamo Indians. In Evolutionary Biology and Human Social Behavior. N. Chagnon & W. Irons, eds. Pp. 98)

"I might add that all women get married, are married young, and married during their entire reproductive period, but not all men are successful in finding wives, and many only do so later in their reproductive life spans. (Chagnon, N.A. (1979) Mate Competition, Favoring Close Kin, and Village Fissioning Among the Yanomamo Indians. In Evolutionary Biology and Human Social Behavior. N. Chagnon & W. Irons, eds. Pp. 97)

"In addition, displays of masculinity, such as fighting prowess and "waiter" (ferocity) are admired by Yanomamo women, and particularly aggressive men have an advantage both in soliciting the sxual favor of larger numbers of women as well as depressing the temptation of other men to seduce their wives." (Chagnon, N.A. (1979) Mate Competition, Favoring Close Kin, and Village Fissioning Among the Yanomamo Indians. In Evolutionary Biology and Human Social Behavior. N. Chagnon & W. Irons, eds. Pp. 101)

"Ethnographic discussions of infanticide in all these contexts can be readily found in the anthropological literature (cf. Alexancer 1974; Dickeman 1975). For example, droughts (environmental flux) commonly cited as a reason for infanticide practices (the Australian aborigines; Basedow 1925; Bates 1944). the destruction of malformed infants occurs among the Yanomano (infra) and has been widely reported in the anthropological literature (cf. Dickeman 1975 and references there, as well as Dickemann, this volume, chapter 13). Optimal distribution of parental expenditure may require the spacing of offspring beyond the human physiological potential. With multiple births the destruction of one or more of the newborn is commonly reported (Metraux 1946; Grantzberg 1973; see bibliography in Dickeman 1975 and Dickemann's references, this volume; Alexander 1974). Other anthropologists have noted the taxing problems of parental care and the difficulities in rearing more children then local domestic and economic conditions might permit: Birdsell (1968) has argued that "...children who cannot be reared are frequently conceived and born. The solution is systematic infanticide" " (Chagnon, N.A., et. al. (1979) Sex-Ratio Variation among the Yanomamo Indians In Evolutionary Biology and Human Social Behavior. N. Chagnon & W. Irons, eds. Pp. 294)

"Yanomamo infants, both male and female, are likely to be destroyed at birth or to suffer a higher risk of mortality due to systematic neglect, conscious or unconscious, for a variety of reasons other than a parent's preference for a child of one sex or the other. These include cases of physical abnormality, paternity uncertainty, and problems in the spacing of births." (Chagnon, N.A., et. al. (1979) Sex-Ratio Variation among the Yanomamo Indians In Evolutionary Biology and Human Social Behavior. N. Chagnon & W. Irons, eds. Pp. 303)

"The arrival of a new infant before an existing one has already made it through the initial hazardous years leads some Yanomamo mothers to destroy the newborn in order to enhance the surivival chances of an older, but still heavily dependent, child." (Chagnon, N.A., et. al. (1979) Sex-Ratio Variation among the Yanomamo Indians In Evolutionary Biology and Human Social Behavior. N. Chagnon & W. Irons, eds. Pp. 305)

Birth interval information in Yanomamo society suggesting males killed as often as females. (Chagnon, N.A., et. al. (1979) Sex-Ratio Variation among the Yanomamo Indians In Evolutionary Biology and Human Social Behavior. N. Chagnon & W. Irons, eds. Pp. 306)

"The variations in adult reproductive success and subsequent higher male mortality lead tothe expectation of a correspondingly male-biased sex ratio at birth. Males are represented in the sex ratio at birth reported by the Yanomamo in a ratio of 129 for every 100 females "births." If it is assumed that the true sex ratio of offspring at birth is consistent with the world wide average of 105 (Colombo 1957), it can be estimated that some twenty percent of all female children actually born were destroyed for reasons having to do with parental preferences for male offspring (cf. Neel and Weiss 1975)." (Chagnon, N.A., et. al. (1979) Sex-Ratio Variation among the Yanomamo Indians In Evolutionary Biology and Human Social Behavior. N. Chagnon & W. Irons, eds. Pp. 308)

"However, the average sex ratio of offspring produced by headman (110) is not significantly different than non-headman's (121). The average sex ratio of offspring for headmen does not vary with social status as might be predicted by the Trivers-Willard Theory." (Chagnon, N.A., et. al. (1979) Sex-Ratio Variation among the Yanomamo Indians In Evolutionary Biology and Human Social Behavior. N. Chagnon & W. Irons, eds. Pp. 319)

[citations removed] "But why did these early pair-bonds need to be permanent? Perhaps like foxes and robins, our ancestors only needed to form pair-bonds long enough to rear their young through infancy. what made me think of this was a remarkable correlation between the length of human infancy in traditional societies, about four years, and the length of many marriages, about four years. Among the traditional !Kung, mothers hold their infants near their skin, breast-feed regularly through the day and night, nurse on demand, and offer their breasts as pacifiers. As a result of this constant body contact and nipple stimulation, as well as high levels of exercise and a low-fat diet, ovulation is suppressed and the ability to become pregnant is postponed for about three years. Hence !Kung births are about four years apart. Four years is the usual period between successive births among continually breast-feeding Australian aborigenes and the Gainj of New Guinea. Infants are generally also weaned around the fourth year among the Yanomamo of Amazonia, the Netsilik Eskimos, the Lepcha of Sikkim, and the Dani of New Guinea. Although birth spacing varies among populations of hunter-gatherers, and maternal age and number of children previously born to a woman affect birth intervals, these data have led anthropologist Jame Lancaster and others to conclude that a four-year pattern of continual nursing through the day and night--was the regular pattern of birth spacing during our long evolutionary past. Thus the modern worldwide divorce peak--about four years--conforms to the traditional period between human successive births--four years. So here is my theory. Like pair-bonding in foxes, robins, and many other species that mate only through a breeding season, human pair-bonds originally evolved to last only long enough to raise a single dependent child through infancy, the first four years, unless a second infant was conceived." (Fisher, H. (1992) Anatomy of Love: The Mysteries of Mating, Marriage, and Why We Stray. Simon & Schuster, New York, 1992. pp. 153-4)

"Differential variation in adult reproductive success is determined in the mechanics of the mating system. First, the practice of polygyny by the Yanomamo results in some men having a disproportionate access to mates. Second, older and politically prominent widowers are likely to take young women as new wives, excluding younger men from early opportunities to reproduce. The net result is the while the sexes are nearly equally represented as adults (see below), male-male competition for wives ensures that only a fraction of adult males will dominate the reproductive contribution made from one generation to the next by females." (Chagnon, N.A., et. al. (1979) Sex-Ratio Variation among the Yanomamo Indians In Evolutionary Biology and Human Social Behavior. N. Chagnon & W. Irons, eds. Pp. 306)

"On the contrary, the Yanomamo appear to be getting five times the minimum daily protein requirement established by the World Health Organization." (Chagnon, N.A., et. al. (1979) Sex-Ratio Variation among the Yanomamo Indians In Evolutionary Biology and Human Social Behavior. N. Chagnon & W. Irons, eds. Pp. 296)


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