Children killed by genetic parents versus stepparents

Abstract

Despite many empirical studies of children killed by parents, there has been little theoretical progress. An examination of 378 cases in a national register revealed that circumstances differed for genetic parents versus stepparents. Infants were at greatest risk of filicide, especially by genetic mothers. Genetic mothers who killed offspring, especially older children, disproportionately had a mental illness and received relatively short sentences, if convicted. Filicides by genetic fathers were disproportionately accompanied by marital discord, suicide, and uxoricide. Filicides by stepparents were disproportionately common and likely to involve ongoing abuse and death by beating. Moreover, if parents also had genetic offspring, their stepchildren were at increased risk of ongoing abuse and neglect prior to death. Poor child health appeared to increase the risk of filicide by genetic mothers, especially as remaining opportunities for childbearing diminished. Although each finding might be consistent with existing lay accounts of filicide (depression, socioeconomic stress, etc.), together, they yielded a pattern uniquely consistent with selectionist accounts based mainly on parental investment theory.

Introduction

Few crimes evoke emotions stronger than those evoked by the killing of a child. That an adult would deliberately cause the death of a child strikes many as inexplicable, especially in the case of filicide—killing one's own child. Yet homicide by family members is a common cause of death among children, especially if death due to neglect is included (Adinkrah, 2001, Adinkrah, 2003, Boudreaux et al., 2001, Goetting, 1988, Lord et al., 2002, Pritchard & Butler, 2003). The risk of filicide decreases with the age of the child (Adinkrah, 2001, Boudreaux et al., 2001, Finkelhor, 1997, Lord et al., 2002, Kunz & Bahr, 1996). At the youngest ages, mothers represent the greatest risk (Adinkrah, 2003, Boudreaux et al., 2001, d'Orban, 1979, Finkelhor, 1997, Holden et al., 1996; Kung & Bahr, 1996;Lord et al., 2002, Xie & Yamagami, 1995). As children age, however, they experience a greater risk of fatal harm from fathers and unrelated members of the household (Adinkrah, 2001, Adinkrah, 2003, Finkelhor, 1997, Goetting, 1988, Kaplun & Reich, 1976, Kasim & Cheah, 1995, Lord et al., 2002, Lucas et al., 2002, Lyman et al., 2003, Marleau et al., 1999, Smithey, 1998, Somander & Rammer, 1991, Strang, 1996).

Mothers who kill newborns are often criminally charged with an offense less than murder, which carries considerably milder sanctions. Infanticide is defined in the Canadian Criminal Code as the killing by a mother of her newborn child when she is mentally disturbed due to either lack of recovery from childbirth or the effect of lactation (Criminal Code, R.S., c.C., 1985, Part VIII, 34, s.216). Research suggests that a mother's killing of her infant is also related to youth, lack of experience, and stressors (such as being uncertain as to which sexual partner is the father of the infant, poverty, and lack of interpersonal support) (Adinkrah, 2001, Adinkrah, 2003, Boudreaux et al., 2001, Haapasalo & Petaja, 1999, Hicks & Gaughan, 1995). Mothers who kill older children are usually seen as having a severe mental illness (Adinkrah, 2001, Bourget & Gagné, 2002, d'Orban, 1979, Haapasalo & Petaja, 1999, Holden et al., 1996, Silverman & Kennedy, 1988, Strang, 1996, Tuteur & Glotzer, 1959, Wilczynski, 1995, Wilczynski, 1997, Xie & Yamagami, 1995, Lewis et al, 1998). In this context, offense details, although horrific, do not typically imply antagonism towards victims. Indeed, the mother often seems to effect a tragic “rescue” by taking the child with her in ending her own life (Adinkrah, 2001, Silverman & Kennedy, 1988).

Fathers who kill their children also often kill themselves, but often seem to have acted out of vengeful anger (Adinkrah, 2001, Adinkrah, 2003, Goetting, 1988, Kaplun & Reich, 1976, Kasim & Cheah, 1995, Lyman et al., 2003, Smithey, 1998). Such homicides seem to be characterized by sexual jealousy, marital discord, marital separation, and even uxoricide (killing one's wife; Adinkrah, 2001, Adinkrah, 2003, Lucas et al., 2002, Marleau et al., 1999, Strang, 1996). Investigators have coined the term “familicide” to describe the killing of children and their mother by the father/husband, often accompanied by a completed or an attempted suicide (Adinkrah, 2001, Adinkrah, 2003, Daly & Wilson, 1988a, Daly & Wilson, 1988b). It is almost unheard of for women to commit such mass family murder (Wilson, Daly, & Daniele, 1995). Overall, men who kill their children are reported to have worse histories of criminal, antisocial, and substance-abusing behaviors (Goetting, 1988, Kaplun & Reich, 1976, Kasim & Cheah, 1995, Pitt & Bale, 1995) than the male population at large, especially so for stepfathers (men acting in a paternal role but not genetically related to the victim) (Goetting, 1988, Hicks & Gaughan, 1995, Kaplun & Reich, 1976, Kasim & Cheah, 1995, Lucas et al., 2002, Lyman et al., 2003).

The clinical literature on human filicide lacks a comprehensive explanation. Prevalent professional accounts of filicide emphasize socioeconomic stressors such as poverty and unemployment (e.g., Belsky, 1993, Finkelhor, 1997, Goetting, 1988), mental illness (Bourget & Gagné, 2002, Goetting, 1988, Marleau et al., 1999, Resnick, 1969, Stroud, 1996, Stroud & Pritchard, 2001, Wilczynski, 1997, Xie & Yamagami, 1995), and marital disharmony (Adinkrah, 2003, Stanton & Simpson, 2002, Somander & Rammer, 1991). In a study of laypeople's explanations of child maltreatment, the prevalent opinions about etiology matched those advanced by experts in the field: poverty and family instability, substance abuse, stressors, moral ignorance, and individual pathology (Korbin, Coulton, Lindstrom-Ufuti, & Spilsbury, 2000). These explanations are insufficiently constrained; how poverty or family breakup induces some parents, but not most, to kill their children is unspecified, for example.

Those unfamiliar with the extensive literature on parent–offspring conflicts across species might wonder, “How could even a slight tendency to kill offspring ever be the result of Darwinian selection?” In mammalian species especially, high levels of parental solicitude represent an obvious and important aspect of reproductive fitness. Within that general tendency, however, a parent's reproductive interests are not isomorphic with those of each offspring. Extensive work (Hrdy, 1979, Hrdy, 1999, Scrimshaw, 1984) has identified five possible bases (the first four of which represent aspects of adaptive function) for offspring killing by parents: (a) sexual selection—reproductive opportunity produced by killing the offspring of another (e.g., killing a prior male's offspring, thereby hastening estrus); (b) parental manipulation—killing that directly improves the parents' reproductive fitness (e.g., killing newborns that would draw resources away from older or future offspring); (c) direct resource competition; (d) resource exploitation (e.g., cannibalism); and (e) pathology. Lay interpretation of human filicide generally implies only the last nonadaptive basis (Hrdy, 1999), but natural selection points to the first two of these as relevant to all filicides, including that by humans.

Among humans, data showing that filicide is associated with circumstances related to net ancestral reproductive fitness would argue for interpretations reflecting manipulation or sexual selection. These accounts depend on selectionist concepts of inclusive reproductive fitness and asymmetric parental investment. Selectionist accounts hypothesize that male reproductive fitness has been associated with proprietary behavior towards their mates. That is, some degree of coercion by men towards women and some degree of suspicion regarding their offspring is to be expected on the grounds that ancestral males who engaged in some form of coercion, threat, and even force to discourage their mates from sexual behavior with other men would be less likely to raise offspring who were not their own and, thus, were more reproductively successful. Threats that the perpetrator was demonstrably willing and able to carry out (in contrast to deliberate bluffing) could be expected to be the most potent of all (Daly & Wilson, 1988a, Daly & Wilson, 1994, Wilson et al., 1995). The result is that human male psychology has an evolutionarily based tendency to regard the sexual alienation of a spouse as a catastrophic loss that is to be resisted via aggressive high-stakes tactics that usually succeed but occasionally backfire, resulting in loss of reproductive fitness. As such, an apparently maladaptive behavior could “represent the tail of some motivational distribution” (Daly & Wilson, 1998a, p. 443). Media reports tell us that a father can be so irrationally distraught or angered by his wife's leaving him for another man that he kills her and her children. The selectionist approach both affords a source for such an extreme emotional reaction and explains why such lethal behavior is so uncommon in response to even the most extreme of life's other tribulations, or among mothers under any circumstances.

Similarly, filicide by stepparents is unlikely to carry direct adaptive advantages (Forbes, 2005), but the clearest example of parents' reproductive interests not coinciding with the child's occurs in stepparenting relationships. Many stepparent relationships are loving; indeed, on selectionist grounds, prospective partners can be expected to exhibit some stepparental solicitude as a hard-to-fake aspect of mating effort. Nevertheless, selectionist work on infanticide (e.g., Hrdy, 1999, McCleary & Chew, 2002, Turke, 1996) demonstrates that, in a world of limited resources, stepparental investment entails greater reproductive cost (and smaller reproductive benefit) than genetic–parental solicitude. Despite its widespread representation in folklore, the association between maltreatment of children and stepparenthood has only rather recently been empirically examined (Wilson, Daly, & Weghorst, 1980). Research motivated by selectionist thinking found that stepparents, compared with genetic parents, represent a much greater risk of violence and death to children, independent of such other risk factors as parental age and poverty (Daly & Wilson, 1998a). The greater tendency of stepfathers to beat children to death in a rage (Daly & Wilson, 1988a, Daly & Wilson, 1994, Weekes-Shackelford & Shackelford, 2004) suggests a failure of solicitude (as distinct from a direct adaptive advantage to homicidal behavior) compared to comparatively painless planned filicides by gunshot or asphyxiation by genetic parents (Weekes-Shackelford & Shackelford, 2004).

There has been very little research on stepmaternal filicide. Because the risks to reproductive success associated with indiscriminant stepparental solicitude are greater for women (who experience much less variability in reproductive success) than for men, women would be expected to exhibit even greater differences in levels of parental solicitude as a function of their status as either genetic mothers or stepmothers. Furthermore, human fatherhood entails more parental uncertainly than motherhood (due to extrapair mating, concealed ovulation, and internal gestation) such that parental solicitude would be expected to be more similar among fathers and stepfathers than between mothers and stepmothers.

Perhaps the most challenging case for laypeople to comprehend—the mother who kills her own child—is most likely to be explained from a selectionist account as having had direct adaptive benefits. Mothers are obliged to invest much in each offspring, through gestation and lactation, and the consequent sacrifice of opportunities to produce other offspring. Thus, they stand to lose much by investing in offspring who would not thrive as well as might later offspring. Occasions on which the mother of an infant elects to let or to cause the child to die are expected to be most common when the child is an infant (relatively few resources have already been expended), the mother is young (she has more prospects for later successful reproduction), her resources are scarce, paternal support is undependable for any reason, or the infant has obvious health problems. These would all be circumstances in which women's ancestral reproductive fitness might have been enhanced by parental manipulation—killing a child in order to devote more resources to older offspring or to delay reproduction until more favorable circumstances are likely to prevail. Thus, this selectionist account can explain the well-established finding that maternal filicides exhibit a greater inverse relationship with age than child homicides perpetrated by anyone else. The killing of healthy children by genetic mothers after their first year of life is sufficiently rare that one could hypothesize that it is primarily a true pathology or disorder (Daly & Wilson, 1988a). Following Wakefield (1992), we define a “disorder” as a harmful dysfunction (i.e., the failure of a mechanism to perform the function for which it was designed by natural selection). Compared to all other perpetrators, genetic mothers who kill noninfants are more likely to be diagnosed with serious mental disorders and to be excused on account of insanity.

The explanatory utility of a selectionist account lies on its ability to make sense of the overall pattern of child homicide by humans, including comparisons between male and female perpetrators, between genetic and stepparental perpetrators, and even between maternal perpetrators of infants versus maternal perpetrators of older children (Janson & van Schaik, 2000). It does not simply account for Cinderella's treatment at the hands of her stepmother (Daly & Wilson, 1998b), but uniquely predicts how she would be treated differently by her mother, father, or stepfather, or indeed by her stepmother had there been no stepsisters. The issue addressed by the present research is the accommodation of proximal (and often apparently pathological) factors related to individual findings pertaining to filicide by more distal selectionist hypotheses.

There is limited research on children killed by stepmothers, and little of the research on human filicide has systematically compared all four categories of perpetrators (genetic mothers, genetic fathers, stepmothers, and stepfathers) and cases in which children were killed by nonfamilial adults. As well, few previous studies have examined the circumstances of the offenses in detail, in part because research has relied on general registers containing limited data on the offense. The present study employed detailed materials gathered by police investigators in the form of a standardized investigative database, permitting us to compare the manner of death of children killed by genetic parents and stepparents with that by nonfamilial adults, and to examine three of the hypothetical bases for filicide suggested by selectionist accounts. Specifically, we hypothesized that pathological factors would most characterize filicide by genetic mothers of older victims because those offenses are least likely to serve the perpetrator's reproductive fitness. Thus, consistent with prior research, we expected that mental illness and legal findings of insanity would be most common among genetic mothers killing older children.

We hypothesized that parental manipulation would, however, characterize many other filicides by genetic mothers, especially young mothers of infant victims, or unhealthy older victims. Thus, and consistent with prior research, we expected that sadness or despair, rather than hostility, would be most common among genetic mothers killing infants and that the manner of causing death would be comparatively painless rather than implying anger or rage. As well, some mental illnesses (especially depression) were expected to be associated with the lack of personal and material resources. We also hypothesized that filicide by fathers, especially genetic fathers, would be characterized by coercive tactics aimed at controlling the reproductive behavior of mates. We regarded this form of filicide as a behavioral “tail end” of parental manipulation. Thus, and consistent with previous research, prior marital discord and conflict, and uxoricide, familicide, and suicide would be most common among fathers, and especially among genetic fathers.

Among stepparents, and especially stepmothers, we hypothesized that evidence of weaker parental solicitude and resource competition would be most common. Thus, and consistent with prior research, stepparents would represent a greater risk of filicide than would genetic parents. In addition, denial of resources (i.e., neglect) and reduced parental solicitude in the form of prior abuse and overt hostility, anger, rage, and beating to death would be most common among filicides by stepparents. In particular, we hypothesized that the reproductive costs of stepparental solitude are greater for women than for men; thus (novel to this study), previous neglect and abuse, anger/rage, and beating to death would be most common among filicides by stepmothers. We further hypothesized that the effect of direct resource competition would be heightened by the presence of offspring genetically related to the perpetrator; thus (novel to this study), genetic offspring would be associated with worse previous abuse and neglect by stepparents.