The Effect: Parental Discrimination against Stepchildren The : Parental Discrimination against Stepchildren

Cinderella stories about abused stepchildren are cross-culturally universal. Are they founded in reality? Because Darwinian selection shapes social motives and behavi- our to be effectively nepotistic, an obvious hypothesis is that stepparents will be over- represented among those who mistreat children. This possibility was long neglected, but stepparenthood has turned out to be the most powerful epidemiological risk fact- or for and child yet known. Moreover, non-violent discriminati- on against stepchildren is substantial and ubiquitous.

Martin Daly, Professor, , Professor, Department of , Department of Psychology, McMaster University McMaster University

Parents are Discriminative Nepotists selectively toward close relatives of the caretaker. A cornerstone of is the Usually, this means the caretaker’s own offspring. proposition that Darwinian selection shapes social Imagine a population of animals in which there are motives and behaviour to be effectively »nepotis- two alternative, heritable types of parental psyche. tic«, that is, to contribute selectively to the well-be- Type A invests its time and energy selectively in the ing and eventual reproduction of the actors’ genetic care of its own young, who are better than average relatives. In any species, the genes and traits that bets to be carriers of the same heritable tendencies. persist and proliferate over generations are those Type B nurtures any youngster in need, regardless whose direct and indirect effects cause them to of which type of behaviour it will display when it replicate at higher rates than alternative genes and later becomes a itself. If that is the sum total traits. captured this point, the of their differences, then the more discriminative essence of modern Darwinism, in his famous phrase type A will assuredly increase in prevalence at the »the selfish gene«.1 expense of type B. One implication of this proposition is that the This point now seems rather obvious. However, care of dependent young will ordinarily be directed for a century after Darwin first described the pro-

SAMFUNDSØKONOMEN NR. 4 – 2002 39 The Cinderella Effect: Parental Discrimination against Stepchildren cess that he called »«, such impli- like those of guillemots, and if an experimenter cations of his theory were poorly appreciated. Be- places an unrelated egg or chick in a razorbill nest, fore the sociobiological revolution of the mid- the will nurture it as they would their own.6 1960s, many biologists subscribed uncritically to Discriminative parental solicitude in mammals the view that the attributes that natural selection follows the same principle.7 In those species, such favours must be those which best promote »the sur- as rats, who sequester and defend immobile pups in vival and reproduction of the species«. This view, isolated burrows, parents do not initially recognize which the English philosopher Helena Cronin has their young as individuals. Individual recognition aptly labelled »greater goodism«,2 was wrong. develops just before the pups become sufficiently A 1962 monograph on the reproductive behav- mobile that mix-ups might have occurred in the iour of a small mammal called the Mexican free- EEA. In other species such as sheep and horses, tailed bat provides an instructive example.3 Observ- however, young can mingle with those of other ing that thousands of helpless pups were left togeth- mothers very soon after birth, and an indiscriminate er in a squirming mass each night while their nurs- mother would be at risk of misdirecting her parental ing mothers went out foraging, researchers blithely nurture even on the day of birth. In these species, concluded that when females return in the morning, specialized brain mechanisms are dedicated to the they must nurse the pups at random, thus constitut- task of establishing an individualized bond between ing an »anonymous dairy herd«. But only a few a mother and her newborn at birth, and the mother years later, the greater goodism implicit in such in- will subsequently reject or even attack unrelated ferences had been critically dissected and demol- milk thieves of the same age and infantile appeal as ished,4 and such a conclusion could no longer be the youngster she is cherishing. In sum, there is no- published in a reputable biological journal without thing magical about parental discrimination: prefer- explicit discussion of the formidable theoretical ential treatment of one’s own young exists only grounds for thinking it must be wrong. The problem where a species’ ecology demands it, and is accom- facing the idea of an anonymous dairy herd is that it plished by means of evolved psychological mecha- is difficult to envision how costly lactation could be nisms for attending and responding to specific cues evolutionarily stable in such a case, since selection that helped parents behave in an appropriately dis- would surely favour those females who expended criminative manner in the EEA. We know of no rea- the least lactational effort and left their pups to be son why the of the human psyche should fed by others. It should thus be no surprise that the have been exempt from this logic. anonymous dairy herd idea turned out to be wrong: the mother bats are now known to possess remark- Stepparents are Over-represented able adaptations for finding and feeding their own as Perpetrators of Abuse and Homicide pups.5 In 1976, we were among the participants in an ani- The psychological adaptations that produce dis- mal behaviour seminar discussing »sexually select- criminative parental solicitude vary between spe- ed «. This term refers to the lethal result cies, in ways that reflect regularities in each spe- of natural selection in favour of those who kill any cies’ ancestral environment of evolutionary adap- dependent offspring encumbering newly acquired tiveness (EEA). The guillemot is a marine bird that mates and thereby accelerate the timing of their lays its eggs on rocky ledges only a few centimetres own reproduction. Such behaviour was then well from nesting neighbours. Guillemots recognize documented only in and in one species of their newly hatched chicks and even their eggs on monkey, but it has since been shown to occur in the basis of individual markings, and reject any un- many other animals, and in both sexes, albeit main- related chicks or eggs that turn up in the nest unin- ly in males.8 During the discussion, a graduate stu- vited. The razorbill is a closely related species that dent raised the question of whether there might be nests in the same habitat, but with a crucial differ- any truth to the stereotype of »wicked« human step- ence: nests are dispersed and spontaneous transpo- parents, as illustrated by Cinderella and many other sitions of chicks and eggs do not occur. In the ab- folktales. Might stepparents be disproportionately sence of selection for chick and egg recognition, ra- responsible for various sorts of child maltreatment? zorbills have not evolved discriminative abilities To our considerable surprise, we soon learned that

SAMFUNDSØKONOMEN NR. 4 – 2002 40 The Cinderella Effect: Parental Discrimination against Stepchildren this question had never been asked in the large and the victims of validated physical abuse as those liv- rapidly growing literature on child abuse, and we ing with both their genetic parents.10 therefore set out to answer it ourselves.9 There are several reasons to be cautious when in- In our first study of this issue, we used an ar- terpreting such evidence. One is that the detection chive of 87,789 legally mandated and subsequently or reporting of abuse may be biased: if there is a validated reports of child maltreatment in the Unit- stereotype to the effect that stepparents are hostile ed States, in conjunction with available estimates of and potentially abusive, then ambiguous evidence the prevalence of various living arrangements may be more likely to be followed up and eventual- among children in the relevant population at large, ly validated when a stepparent is involved. But al- to estimate rates of abuse in various sorts of house- though such biases may exist, we were certain that holds and by various categories of »parents«. Be- they could not explain away the over-representation cause the US census did not distinguish stepparents of stepparents as abusers, for the following reasons. from genetic parents, there were no solid data on As the severity of child abuse increases, up to the the incidence of steprelationships in the general extreme of lethal battering, it becomes increasingly population, so we made our comparisons conserva- unambiguous and difficult to hide, and distortions tive by adopting an estimate from the literature due to biased detection and reporting should there- whose simplifying assumptions guaranteed that it fore shrink. However, as we narrowed the case cri- would be too high. But despite handicapping the teria in such a way as to make them increasingly se- hypothesis in this way, a substantial degree of ex- vere and unequivocal, the overrepresentation of cess risk at the hands of stepparents was still appar- stepparents as abusers increased, rather than shrink- ent. For example, children under three years of age ing, and when we considered only the 279 fatal cas- who dwelt with one genetic parent and one steppar- es, the estimated rates in stepparent-plus-genetic- ent were estimated to be seven times as likely to be parent homes had risen to approximately one hun-

Figure 1. Age-specific rates of child homicide perpetrated by genetic parents versus stepparents in , 1974-1990, based on all cases known to Canadian police forces.

Genetic Step Parents Parents

Homicides per Million Parent-Child Dyads per Annum

SAMFUNDSØKONOMEN NR. 4 – 2002 41 The Cinderella Effect: Parental Discrimination against Stepchildren dred times greater than in two-genetic-parent who kill are often deeply depressed, and may even homes. construe -suicide as a humane act of rescue, This study left little doubt that elevated abuse whereas homicidal stepparents are seldom suicidal risk in was genuine and huge, but that and typically betray hostility to their victims by the does not necessarily mean that steprelationship it- relative brutality of their lethal acts. In Canada, for self was to blame. Because the study was correla- example, 44 of 155 men (28%) who killed their pre- tional, rather than experimental, we cannot readily school-age children during a 17-year period did so rule out the possibility that stepparenthood was as- in the context of a completed suicide, compared sociated with some other factor of more direct with just 1 of 66 men who killed stepchildren, and causal relevance. One obvious possibility is that whereas 82% of the victims of stepfathers were poverty might constitute such a »confounding« beaten to death, the majority of children slain by variable, but this hypothesis could also be rejected, their genetic fathers were killed by less assaultive since survey data showed that the income distribu- means. These contrasts are replicated in British cas- tion of step-parent-plus-genetic-parent households es. was virtually identical to that for two-genetic-parent Studies in several other countries, using a variety households. Low-income were indeed of methods, have also uncovered large differences over-represented in the abuse data archive, but the between stepparents and genetic parents with re- association between abuse and poverty was inde- spect to abusive treatment of children. In , pendent of that between abuse and steprelationship. stepfathers are even more extremely over-represent- Our subsequent research in Canada has told es- ed as lethal baby batterers than in Canada, Britain sentially the same story. In the city of Hamilton, or the USA.15 In a Korean study of schoolchildren where we live, we found that about 1 out of every in the 3rd and 4th grades, 40% of those living with 3000 pre-schoolers living with two genetic parents a stepparent and a genetic parent were reported to was reported as a victim to the provincial child be »seriously battered« once a month or more, com- abuse registry in a 12-month period, compared to 1 pared to 7% of those living with both their genetic in 75 for those living with a genetic parent and a parents.16 In Finland, 3.7% of 15-year-old girls liv- stepparent.11 Poverty was again a distinct risk factor ing with a stepfather claimed that he had abused in this study, and maternal youth and the number of them sexually, compared to 0.2% of those living children in the home were shown to be additional with their genetic fathers.17 Many other examples risk factors that were independent of the large ef- could be enumerated. fects of steprelationship. The hypothesis that step- Although the over-representation of stepchildren parents are frequent abusers merely because those as victims of abuse is widespread, widely docu- who remarry include disproportionate numbers of mented, and often extremely large, several authors violent personality types was also eliminated by the have tried to refute it. One influential counter- demonstration that abusive stepparents were usually claim, by Richard Gelles and John Harrop, was discriminative in their targets, treating their own based on a telephone survey in which 117 US step- offspring well. parents who agreed to be interviewed about conflict We then went on to analyze Canadian national and violence in their families were no more likely homicide data, and as with the fatal abuse cases in than genetic parents to admit to having assaulted the , we found excess risk at the hands their children in anger.18 Perhaps the most interest- of stepparents to be even more extreme than was ing thing about this study is that it has been taken the case for non-lethal abuse.12 It is clear that the seriously. The American Medical Association, for situation is similar in Great Britain, although esti- example, cited it as their rationale for excluding mates of the numbers of stepchildren in the British stepparenthood, the most powerful epidemiological population at large are imprecise.13, 14 Moreover, be- risk factor for severe child maltreatment yet discov- sides demonstrating that stepchildren are killed at ered, from a check-list for physicians screen- relatively high rates, our analyses of Canadian and ing for child abuse,19 and many other re- British homicide cases have shown that searchers have accepted the claim that by phoning a by stepparents are qualitatively different from those random sample of US homes, Gelles and Harrop perpetrated by genetic parents.13 Genetic parents achieved a result of greater validity than could ever

SAMFUNDSØKONOMEN NR. 4 – 2002 42 The Cinderella Effect: Parental Discrimination against Stepchildren be garnered from »biased« reports of children’s in- interpreted as non-adaptive byproducts of an adap- juries and deaths. tation, namely the nepotistic bias in parental solici- Other counter-claims have been based on ele- tude. It is scarcely plausible that non-lethal child mentary statistical errors. Psychologists Louise Sil- abuse could be an adaptation, for what does it verstein and Carl Auerbach,20 for example, noted achieve? The recurrent abuse that many stepchil- that 29% of a sample of US child vic- dren suffer is more likely to elevate the perpetra- tims were molested by birth parents, 25% by substi- tor’s costs of investing in the child than to lower tute parents, and 46% by someone else, and con- them.11 cluded that »these statistics do not support the neo- At first glance, stepparental homicide looks like conservative contention (sic) that stepfathers… a better candidate for an evolved adaptation, by abuse children more frequently than biological fa- analogy with the sexually selected infanticide ob- thers« (p 402); these authors apparently failed to served in some other species, including several pri- grasp that most children do not have »substitute mates. But this idea is really no more plausible than parents« and that the quoted statistics reflected that of adaptive non-lethal abuse. Homicides by massively higher rates of sexual molestation of the stepparents are seldom carried out in an »efficient« minority who do. Catherine Malkin and Michael manner; they often evoke retributive justice from Lamb21 analyzed data on family circumstances of the victim’s genetic kin or the community; and they US child abuse victims, without making any refer- are apparently more likely to deprive the perpetrator ence whatever to the relevant figures for the general of future reproductive opportunities with the vic- population, and drew the scarcely comprehensible tim’s genetic parent than to speed things up. Al- conclusion that »biological parents were more though it is possible that these costs and benefits rather than less likely than nonbiological parents to were different in the EEA, no evidence in support abuse severely and to kill rather than cause major of such a conjecture can be found in ethnographic physical injuries to their children« (p 129). Al- studies of human behaviour in small-scale, face-to- though 39% of the child victims from 2-parent fam- face societies like those in which the human psyche ilies in their data set had a stepparent, compared to presumably evolved. Thus, the most plausible inter- an age-matched expectation from population data of pretation of the high prevalence of stepchildren less than 5%, and although every form of abuse was among abuse victims is simply that stepparents perpetrated at massively higher rates by stepparents the children in their care less, and resent them than by genetic parents,22 Malkin and Lamb appar- more, on average, than genetic parents. Differential ently imagined that they had failed to replicate prior violence is a relatively rare and extreme reflection reports of such a difference, and their conclusion to of something much more general, namely differen- that effect has been widely cited. Finally, Hans tial parental solicitude. Temrin and collaborators reported that Swedish If this claim is correct, we should expect to find children suffered no excess risk of homicide at the that stepchildren are disadvantaged in a broad array hands of stepparents,23 a mistaken inference that de- of other, less violent domains, and that this is true rived from their failure to take account of the fact not just of an unlucky few, but quite generally. A that the proportion of all children who have steppar- substantial body of recent research has confirmed ents is near zero at birth and increases steadily with this expectation. One large national probability age; in fact, although the number of homicides was sample survey study in the US, for example, small, their data exhibited a highly significant 8- showed that the financial support that families pro- fold difference in risk among pre-schoolers.22 vide for higher education is substantially reduced for stepchildren, even when both parental wealth Discrimination against Stepchildren and the child’s scholastic record are statistically goes beyond Violence controlled.24 Not surprisingly, stepchildren have re- The fact that stepparents mistreat children at rela- peatedly been found to leave school at earlier ages tively high rates cannot be taken as evidence that than other children, and also to leave home earlier. such behaviour represents an adaptive »strategy« In Britain, the National Study that has been directly favoured by selection. The demonstrated that both the genetic parent and the abuse and murder of stepchildren are more readily stepparent express low aspirations for the children’s

SAMFUNDSØKONOMEN NR. 4 – 2002 43 The Cinderella Effect: Parental Discrimination against Stepchildren education in stepparent homes, lower even than the tently and cumulatively asymmetrical, and parents aspirations of single mothers, and that the children’s derive joy, rather than resentment, from being thus own aspirations follow suit.25 Further American exploited! Why this should be so is easy to under- studies, again controlled for parental means, have stand. Animals, including people, have evolved to demonstrated that children living with stepmothers expend their hard-won resources, and indeed their do not receive the same regular medical and dental very lives, in the production and rearing of »fitness care that children living with their genetic parents vehicles«: healthy offspring who are good prospects can expect, and even that less money is spent on to reproduce in their turn. food in stepmother households; these deficits are ei- The time, energy and love that parents invest in ther smaller or non-existent in stepfather house- their young are valuable resources and selection has holds, presumably because US wives take primary shaped parental psyches to guard against parasitism responsibility for the children’s health care and do and allocate them carefully, in ways that would most of the family food shopping.26 Other evidence have promoted parental fitness in the EEA. Why, of differential economic investments in genetic off- then, is any creature ever willing to assume the role spring versus stepchildren has been gathered in of stepparent? The answer appears to be that step- countries ranging from Finland to (ref- is an aspect of courtship: one component erences in 22). of the mutual considerations that new mates negoti- There is also a large body of survey research ate in species in which couples engage in complex concerning the quality of stepfamily life. Consistent cooperation and are likely to stay together for a findings are that stepparents and stepchildren alike long time.32 Steprelationships were certainly preva- rate their relationship as less close and less depend- lent in the human EEA, and must have been impor- able as a source of both emotional and material sup- tant selective forces, for although stepparental in- port, and that all parties in stepfamilies are less sat- vestment has its utility, it would surely have been a isfied, on average, than persons living in intact first mistake to embrace the role with the same selfless families.27 Not surprisingly, the presence of devotion as genetic parents. And of course, steppar- stepchildren is also associated with elevated rates of ents do not embrace their parental role with the marital dissolution27 and marital violence.28 An ob- commitment characteristic of genetic parents. Few servational study in Trinidad by anthropologist profess love for their wards, and unlike genetic par- was the first to provide direct behav- ent-offspring relationships, those between steppar- ioural evidence that men provide less nurturant at- ents and their stepchildren typically end if the mar- tention to stepchildren than to their genetic off- riage that created them dissolves. spring, and that the differences in how they treat the Lest we leave the impression that successful two groups of children are attenuated in the moth- steprelationships are an impossible dream, it is er’s presence.29 Anthropologist Frank Marlowe has worth stressing that they often work reasonably made similar, though less extensive, observations well. Although violent abuse is far more prevalent among Hadza foragers in ; one striking re- in stepfamilies than in genetic parent homes, it still sult was that Hadza men were never observed to occurs in only a tiny minority of cases. Although with their stepchildren.30 Subsequent work by few stepparents and stepchildren say they love one Flinn in Dominica has shown that stepchildren have another, a great many profess some degree of mutu- chronically elevated levels of the stress hormone al affection and respect. Many, perhaps most, step- cortisol.31 It seems clear that stepfamily life is diffi- parents derive pleasure from helping raise the cult, the world round. beloved child of a beloved partner, and many, per- haps most, stepchildren are better off than they Parental Affection is Profound would have been had the genetic parent never re- Successful social relations with a spouse, a friend, a married. But this is not to say that stepparents often colleague at work, or even a sibling typically entail come to feel the selfless commitment that is so a reciprocal exchange of benefits. If one party con- common in genetic parents. They don’t. sistently takes without giving, the relationship Many social scientists apparently dislike the sours. But parent-offspring relations are very differ- proposition that parental love is special and is sel- ent, indeed unique: the flow of resources is consis- dom fully activated in stepparents. A popular »alter-

SAMFUNDSØKONOMEN NR. 4 – 2002 44 The Cinderella Effect: Parental Discrimination against Stepchildren native« is to argue that the differences between ge- and this and other areas of social science would netic parents and stepparents occur because steppar- surely benefit from greater sophistication about the ents were not in contact with the children from the evolutionary process and its relevance to human af- time of birth and therefore never »bonded« proper- fairs. ly. Of course, even if this were true, it would not re- Ironically, it is not evolutionary psychologists ally be an alternative to the proposition that natural who denigrate human beings as simple automata, selection shaped this »bonding« response to effec- but those who adhere to the implausible notion that tuate nepotistic favouritism in the EEA, but be that stepparenthood is psychologically equivalent to ge- as it may, the only study that has addressed this hy- netic parenthood and that »bonding« experience is pothesis speaks against it. Flinn’s Trinidad study in- sufficient to evoke the full depth of parental feeling. cluded a sample of men who established cohabiting Evolutionary psychologists have much more respect relationships with women pregnant by other men, for human complexity than that. and who were therefore resident father figures when their stepchildren were born. These men exhibited higher levels of and hostility than step- Noter fathers who joined the household later,29 a striking 1. Dawkins R. 1976. The selfish gene. Oxford: Oxford Uni- result which we interpret as a response to resented versity Press. social pressures or presumptions that they should 2. Cronin H. (1992) The ant and the peacock. Cambridge act like true fathers. UK: Cambridge University Press.

Concluding Remarks 3. Davis R.B., Herreid C.F. & Short H.L. (1962) Mexican The evolutionary reasoning that inspired and con- free-tailed bats in Texas. Ecological Monographs 32: 311- tinues to inform our research is consistent with 346. common wisdom. Parents love their children. This 4. The demolition of greater goodism was accomplished pri- love is profound and not readily substitutable. Step- marily by Williams’s critique (Williams G.C. 1966. Adapta- parents usually love the children less, or not at all, tion and natural selection. Princeton USA: Princeton Univer- and many would really rather that the children, who sity Press) and by Hamilton’s postulation of the theory of »in- entered into the remarriage negotiations as costs, clusive fitness« (Hamilton W.D. 1964. The genetical evolu- tion of social behaviour I and II. Journal of Theoretical Biol- not benefits, had never been born. Higher rates of ogy 7: 1-52). child maltreatment by stepparents than by genetic parents are predictable byproducts of these differ- 5. McCracken, G.F. & Gustin M.K. 1992. Nursing behavior ences in love and commitment. in Mexican free-tailed bat maternity colonies. Ethology 89: There is little in these propositions that would 305-321. inspire dissent from the proverbial man on the 6. Birkhead, T.R. (1978) Behavioural adaptations to high den- street; there is little that he would consider news. sity nesting in the common guillemot, Uria aalge. Animal Be- Curiously, however, these propositions and the em- haviour 26: 321-331. pirical evidence in their favour have encountered a steady stream of muddled, indignant denials, in 7. Daly M. & Wilson M.I. 1995. Discriminative parental so- both the professional literature and in the popular licitude and the relevance of evolutionary models to the press. Why? One reason seems to be that many analysis of motivational systems. In M.S. Gazzaniga, ed., The commentators realize that stepfamily life is diffi- cognitive neurosciences. Cambridge USA: MIT Press. cult, and believe that publicizing its more dramatic 8. Parmigiami S. & vom Saal F.S., eds. (1994) Infanticide failures »stigmatizes« stepparents and makes their and parental care. Chur, Switzerland: Harwood Academic task all the harder. Many also suffer from the mis- Publishers. conception that a »biological« explanation for step- parental violence is a claim of its inevitability and 9. Daly M. & Wilson M. 1998. The truth about Cinderella. imperviousness to social controls, which, if accept- London: Weidenfeld & Nicholson. ed, will excuse the violence. These misunderstand- 10. Wilson M., Daly M. & Weghorst, S.J. 1980. Household ings are an impediment to progress in understand- composition and the risk of child abuse and neglect. Journal ing and remediating the mistreatment of children, of Biosocial Science 12: 333-340.

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11. Daly M. & Wilson M.I. 1985. Child abuse and other risks 22. Daly M. & Wilson M. (2001) An assessment of some pro- of not living with both parents. Ethology & 6: posed exceptions to the phenomenon of nepotistic discrimina- 197-210. tion against stepchildren. Annales Zoologici Fennici 38: 287- 296. 12. Daly M. & Wilson M.I. 1988. Evolutionary social psy- chology and family homicide. Science 242: 519-524. 23. Temrin H., Buchmayer S. & Enquist M. (2000) Steppar- ents and infanticide: new data contradict evolutionary predic- 13. Daly M. & Wilson M.I. (1994) Some differential attribut- tions. Proceedings of the Royal Society of London B 267: es of lethal assaults on small children by stepfathers versus 943-945. genetic fathers. Ethology & Sociobiology 15: 207-217. 24. Zvoch K. (1999) Family type and investment in educa- 14. Creighton S.J. (1985) An epidemiological study of abused tion: a comparison of genetic and stepparent families. Evolu- children and their families in the United Kingdom between tion & Human Behavior 20: 453-464. 1977 and 1982. Child Abuse & Neglect 9: 441-448. 25. Ferri E. (1984) Stepchildren: a national study. Windsor, 15. Wallace A. (1986) Homicide: the social reality. Sydney: UK: NFER-Meslon. New South Wales Bureau of Crime Statistics & Research. 26. Case A. & Paxson C. (2001) Mothers and others: who in- 16. Kim K. & Ko B. (1990) An incidence survey of battered vests in children’s health? Journal of Health Economics 20: children in two elementary schools in Seoul. Child Abuse & 301-328. Case A., Lin I.-F. & McLanahan S. (2000) How Neglect 14: 273-276. hungry is the selfish gene? Economic Journal 110: 781-804.

17. Sariola H. & Uutela A. (1996) The prevalence and context 27. Booth A. & Dunn J., eds. (1994) Stepfamilies: Who bene- of abuse in Finland. Child Abuse & Neglect 20: 843- fits? Who does not? Hillsdale US: Erlbaum. 850. 28. Daly M., Singh L.S. & Wilson M.I. (1993) Children fa- 18. Gelles R.J. & Harrop J.W. (1991) The risk of abusive vio- thered by previous partners: a risk factor for violence against lence among children with nongenetic caretakers. Family Re- women. Canadian Journal of Public Health 84: 209-210. lations 40: 78-83. It is worth noting that even in such tele- Daly M., Wiseman K.A.. & Wilson M.I. (1997) Women with phone surveys, US stepparents have acknowledged striking children sired by previous partners incur excess risk of uxori- the children in their care at much higher rates than genetic cide. Homicide Studies 1: 61-71. parents, when the question was put with reference to punish- ing children for misbehaviour rather than striking them in 29. Flinn M.V. (1988) Step and genetic parent/offspring rela- anger; see Hashima P.Y. & Amato P.R. (1994) Poverty, social tionships in a Caribbean village. Ethology & Sociobiology 9: support, and parental behavior. Child Development 65: 394- 335-369. 403. 30. Marlowe F. (1999) Showoffs or providers? The parenting 19. Council on Scientific Affairs of The American Medical effort of Hadza men. Evolution & Human Behavior 20: 391- Association (1993): Adolescents as victims of family vio- 404. lence. Report of the Council on Scientific Affairs of the American Medical Association. Journal of the American 31. Flinn M.V. & B.G. (1995) Childhood stress and Medical Association 270: 1850-1856. family environment. Current Anthropology 36: 854-866.

20. Silverstein L.B. & Auerbach C.F. (1999) Deconstructing 32. Rohwer S., Herron J.C. & Daly M. (1999) Stepparental the essential father. American Psychologist 54: 397-407. behavior as mating effort in birds and other animals. Evolu- tion & Human Behavior 20: 367-390. 21. Malkin C.M. & Lamb M.E. (1994) Child maltreatment: a test of sociobiological theory. Journal of Comparative Family Studies 25: 121-134.

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