Child Abuse and Neglect

Biosocial Dimensions - Foundations of Human Behavior

Jane B. Lancaster, Richard J. Gelles

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781351529112
• Edition: 1
• Topic: Politics & International Relations
• Subtopic: Politics
• Index: Politics & International Relations

Child Abuse and Neglect is the third volume sponsored by the Social Science Research Council. The goals of these volumes include the development of a biosocial perspective and its application to the interface between biological and social phenomena in order to advance the understanding of human behavior.Child Abuse and Neglect applies the biosocial perspective to child maltreatment and maladaptation in parent-child relations. The biosocial perspective is particularly appropriate for investigating parent behavior since the family is the universal social institution in which children are born and reared, in which cultural traditions and values are transmitted, and in which individuals fulfill their biological potential for reproduction, growth, and development. The volume examines biological substrates and social and environmental contexts as determinants of parent behavior. By identifying areas in which contemporary human parent behaviors conform with and depart from evolutionary and historical patterns and assessing the overall costs and benefits, it permits their objective assessment in terms of modern circumstances. In analyzing evolutionary and historical variations in parent behavior and assessing their costs and benefits, the book makes possible an objective assessment of contemporary variations. Its analysis of the occurrence of child abuse in past history and in other cultures and species advances our ability to predict the probability of child abuse and neglect in various social and ecological contexts.

Part 3

Explaining Child Abuse and Neglect

Chapter 5

Sex-Biased Parental Investment Among Primates and Other Mammals: a Critical Evaluation of the Trivers-Willard Hypothesis

Sarah Blaffer Hrdy

Introduction: Infanticide, Child Neglect, and the Concept of Parental Investment

Infanticide, either by a parent, by another relative, or by an unrelated individual of either sex is a widespread and very variable phenomenon in nature whose comprehension requires multiple explanatory frameworks. To date, the most widely reported form of infanticide among animals involves the killing of infants by unrelated males (e.g., in many species of nonhuman primates and cats and in certain strains of mice and lemmings) or by females with varying degrees of relatedness to the mother (e.g., species of ground squirrels and prairie dogs) (Hausfater and Hrdy, 1984; Hoogland, 1985). Although abandonment of infants or litters is not uncommon, animals in their natural habitats virtually never physically attack or directly destroy their own offspring. Humans, in this respect, are quite unusual among mammals in that across cultures parents themselves are the most likely perpetrators of infanticide through abandonment or even direct killing (these issues are discussed at length in Hausfater and Hrdy, 1984).

The decision to terminate further investment in a particular infant is typically made at birth or shortly after, and the mother is party to the decision (Dickemann, 1975; Minturn and Stashak, 1982; Daly and Wilson, 1984; Scrimshaw, 1984). Infanticide in such instances is probably usefully viewed as a very late form of abortion. From a sociobiological perspective, such parents are viewed as strategists whose ultimate goal is to increase the survival and lifetime breeding prospects of their entire lineage, even if it means a temporary setback in the form of a lost infant. It is assumed that each family has only limited resources to channel into reproduction. Since the time frame at issue is long term, a particular infant may be sacrificed if there is a chance that termination of investmentin a particular infant would, on average, eventually enhance opportunities to perpetuate the lineage. The classic example involves killing the youngest of two closely spaced children, withholding investment from a new infant in order to invest in a healthy, older child already past the perilous first years of life.

Theoretically then, family resources should be allocated according to the degree of relatedness of the parent or stepparent to the infant, how likely a candidate the offspring is for translating parental investment into subsequent reproduction (i.e., offspring quality), as well as according to what other options the parents have for using available resources (Alexander, 1974; Daly and Wilson, 1984 and Chapter 8, this volume). According to this perspective, parents perpetually monitor both the “worth” of particular infants and their probable future demands on family resources (including demands long after weaning, such as marriage dowries), weighing these in the context of current socio-ecological conditions (e.g., anticipated investment from the father or other family members; family economic status; probable food availability) and invest in offspring accordingly (for an illustrative case study, see Bugos and McCarthy, 1984). Along the same lines, several authors have suggested that in some cases, offspring neglect in societies where infanticide is not an option may be a consequence of the same “decision-making” process which reduces parental motivations to invest in a particular infant. Should this happen, additional demands for nurture made on the parent by the infant (or other parties) may result in abuse of the infant.

This conceptual framework derives from a particular model, a hypothetical continuum of parental investment beginning at conception and continuing through weaning and beyond where parents are (at some level) thought to be continuously monitoring the costs and benefits of additional investment. This model is both new and speculative but has already begun to attract attention from researchers in anthropology, biology, and public health (e.g., Hausfater and Hrdy, 1984). Even those subscribing to the model, however, differ in their assessment of how much of contemporary infanticide, and child abuse such a conceptual framework is likely to explain (compare, for example, Daly and Wilson, 1980 with Lenington, 1981). In my own opinion the model has the widest explanatory scope at low levels of subsistence (e.g., as among societies like the Ayoreo [Bugos and McCarthy, 1984]) and the narrowest in societies like our own which are (at least temporarily) characterized by a state of “ecological release.” Starvation is uncommon, and parents virtually never benefit from killing an infant. In other words, I believe the model addresses itself to only a subset of contemporary western cases, a point dealt with elsewhere (Hrdy and Hausfater, 1984). The model remains relatively untested (see Daly and Wilson, Chapter 9 this volume, for an exception and for a slightly different perspective that stresses psychological motivations rather than outcomes), and the fact is we do not yet know to what extent child neglect and infanticide can be explained by such a model.

Cross-culturally, there appears to be little doubt that most cases of human infanticide seem directly related to parental perceptions of either offspring quality or of the probable quality of the subsistence base in the near future. However, in a small portion of cases, sex of the infant rather than quality per se turns out to be the significant variable. Sex preferential infanticide is uncommon but is reported to occur in nearly 9% of the world’s cultures (Minturn and Stashak, 1982). In some extreme North Indian cases, all daughters born in certain groups are killed at birth, and wives for sons must be recruited from outside of the group (Miller, 1981; Dickemann, 1979).

Traditional preferences for sons in some Indian communities is currently manifested in parental decisions to retain a fetus diagnosed as male or female. Of 700 prenatal diagnoses undertaken at one hospital in Western India between 1976 and 1977, 100% of fetuses diagnosed male contrasted to 5% of fetuses diagnosed female were carried to term (Ramanamma and Bambawale, 1980). We can not know how typical the sample for this controversial study is, but it does clearly document a continuing and drastic preference for sons in some parts of the world. The incidence of preferential male infanticide is certainly low, and its practice has been reported for 1-4% of human cultures (Minturn and Stashak, 1982; Whyte, 1978).

Even where parents do not practice outright infanticide, other forms of sex-biased investment by parents are widespread. As Johansson (this volume, Chapter 4) points out, differential provisioning of sons and daughters is one of the primary modes of biasing parental investment. Reports of one sex or the other being nursed longer are common in the ethnographic and historical literature, and such phenomena are almost certainly underestimated. Among the Wolof of West Africa, for example, females are said to be breast-fed up to 24 months, while males are nursed 18 months (Falade, 1971; cf. Burrows and Spiro, 1957, for the Ifaluk case; Orent, 1975, for the Kafa of Southwest Nigeria; Miller, 1981:90, for various Moslem Middle Eastern examples). The most widely spread bias, however, particularly in Asia, parts of Latin America, and occasionally Europe, appears to be in favor of feeding males more. For a sample of 422 Lebanese infants from the Middle East in a culture where sons are regarded with greater “warmth” than daughters, Prothro reports: “In every group [studied] there were more girls than boys breastfed for less than five months and more boys than girls for more than fourteen months”; these trends were statistically significant (Prothro, 1961:74; see also Tekçe and Shorter, 1984, for Jordan). The nursing ideal for ninth-century France closely resembles that for contemporary Ecuador: Daughters should be nursed an average of 1 year, boys twice that long (McKee, 1982; Coleman, 1976; see also Margery Wolf for Taiwan, cited in McKee, 1982; Gessain, 1963, for Guinea; Khan, 1973, for Northern India). Similar biases are suggested by data on birth spacing where the span of time until the next infant is born is longer after a son than after a daughter (Haldar and Bhattacharyya, 1969; Khan, 1973).

The connection between early weaning and mortality is indirect and therefore difficult to prove. In my opinion, however, there can be little doubt that early curtailment of breast-feeding and the double loss of both nutritional and immunological benefits of mother’s milk renders infants more susceptible to rotavirus and other sources of diarrhea, the world’s major mortality threat to infants in undeveloped countries (Blacklow and Cukor, 1981). Preferential feeding of sons can be viewed as potentially lethal discrimination against daughters. At the same time the alternative possibility, that parents are merely trying to compensate for the greater vulnerability of males by feeding them better or feeding them longer, must also be kept in mind, a point that will be returned to.

Traditional explanations for parental sex preferences, particularly the widespread preference for sons in many cultures (Coombs, 1977; Miller, 1981; Park, 1983) stress: (1) the greater strength of males and their essential contributions to hunting and heavy agricultural work; (2) their importance as warriors and in local disputes; (3) male roles in rituals and in transmission of family names; (4) high cost of dowries in those societies that have dowries (at a bare minimum, 8% of human cultures); and (5) high value placed on males for “ideological” reasons.

There can be little doubt that such factors do indeed play a role. Strong arguments can be marshalled to explain preferential female infanticide among groups like the Copper Eskimo in terms of the importance of hunting by males or female infanticide among the Yano-mamo in terms of the importance of sons needed to wage war and to successfully raid for wives (Balikci, 1967; Chagnon, 1968; see also Divale and Harris, 1976). The ideological arguments, and especially arguments based on male roles in rituals, and dowries, are more problematic simply because one suspects that a strong preference for sons preceded the establishment of these institutions. Similarly the hypothesis that female infanticide can be attributed to low female participation in subsistence (e.g., Miller, 1981) leaves much to be explained, particularly its occurrence in areas where females work very hard and its absence in some areas where women work little.

The failure of traditional explanations to explain a large portion of the known cases of sex bias have led some authors (e.g., Härtung, 1983; Dickemann, 1979a) to consider a sixth explanation, essentially a sociobiological explanation that focuses on the probable reproductive contribution of sons versus daughters under different socioecological conditions. In this realm, the most logically powerful tool to date has been what is now known in evolutionary biology as the “Trivers-Willard hypothesis.”

It should be noted that the Trivers-Willard hypothesis is a very broad one insofar as it applies across species, to many animals as well as to humans; it is also narrow in that it applies only under specialized conditions (detailed in the next section). Even if valid, the Trivers-Willard hypothesis is not going to provide an explanation for all sex-biased investment by parents. Nevertheless, I would contend that to explain even a portion of cases in which parents terminate investment in one sort of offspring while investing in another represents a significant advance in an area where general theories have not previously been used. For the most part, the Trivers-Willard hypothesis has been ignored out of hand by most or else cited as a proved “theory” by a very few. This chapter provides a critical and comprehensive examination and evaluation of the success this hypothesis has had in explaining sex-biased parental investment by parents in primates (including humans) and other mammals.

The Trivers-Willard Hypothesis

An offhand remark by evolutionary biologist Robert Trivers has turned out to be a prophetic one: “Even if I’m wrong, it will take them years to find out.” Shortly afterward, in January 1973, Science published a brief paper by Trivers and his fellow graduate student (from mathematics), Dan Willard. They proposed that “natural selection should favor parental ability to adjust the sex ratio of offspring produced according to parental ability to invest” so that “under certain well-defined conditions, natural selection favors deviations from a 50/50 sex ratio at conception . . .” (1973:90). Specifically, Trivers and Willard thought their model should apply whenever the variance in male reproductive success is greater than that for females (as it is in many polygynous species) and when maternal condition is correlated with subsequent reproductive success of her offspring. Under these conditions, mothers in good condition should bias parental investment toward the sex where it would make the most difference (typically males). Efforts either to refute or validate this hypothesis have resulted in a vast and frequently contradictory literature (reviewed by Williams, 1979; Burley, 1982; Clutton-Brock and Albon, 1982; Charnov, 1982). In addition to these specific models, “Trivers-Willard” has also come to be used as a synonomous term with any sex-biased parental investment—whether before or after birth—that results on average in increased reproductive success for a lineage. In this chapter all three forms of the Trivers-Willard hypothesis are discussed, but it is this more general proposition that will primarily concern us.

The specific hypothesis that parents were facultatively adjusting sex ratios at conception in line with parental ability to invest in offspring has been beset by theoretical problems, by the dearth of information concerning possible mechanisms for facultative adjustment of the sex ratio at conception, and by serious difficulties in documentation. Thirteen years later, opinions about the hypothesis vary. What to some was a triumph for the power of evolutionary logic, with the correct theoretical solution achieved well in advance of any data to support it, has struck others as a foolhardy diversion of energies when it would have been wiser to follow Darwin’s example of delaying judgment on the matter of sex ratios: “I formerly thought that when a tendency to produce the two sexes in equal numbers was advantageous to the species it would follow from natural selection,” Darwin wrote in the revised, second edition 1871/1974:256) of The Descent of Man, “But I now see that the whole problem is so intricate that it is safer to leave its solution to the future.” Darwin’s sentiments have, I suspect, rung a chord in virtually every researcher who has tried to make sense of the exasperating literature concerning the adaptiveness for parents of biasing sex ratios toward either sons or daughters.

Biasing Sex Ratios prior to Birth

Theoretical Difficulties

Some 50 years ago it occurred to R.A. Fisher (1930), as it had also occurred in a more general way to Darwin before him (1871/1974), that powerful selective forces would lead parents in panmictic (randomly mating) populations to invest equally in their sons and daughters. Since, in most cases, sons and daughters are about equally costly, equal investment would in most cases lead to equal production of both sexes. If e...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Contents
• Acknowledgments
• List of Contributors
• I Introduction
• II Child Abuse: Cross-Cultural, Historical, and Evolutionary Perspectives
• III Explaining Child Abuse and Neglect
• IV Outcomes And Consequences of Maltreatment
• Index