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February 10, 1998
Genetic Ties May Be Factor in Violence in Stepfamilies
By JANE E. BRODY
woman's live-in boyfriend murders her child fathered by another man. A woman neglects her young stepsister and punishes her so viciously that she dies. A stepfather sexually abuses his wife's daughter by a former husband.
As these examples drawn from news articles over last year demonstrate, the Cinderella story is hardly a fairy tale. Researchers are finding that the incidence of violence and abuse is vastly greater in step-families than in traditional families in which the children are biologically related to both parents and to one other.
Of course, most stepfamilies do well, despite potential stresses. And plenty of families in which all the children are the progeny of both parents are fraught with violence and despair.
But step-families are at much higher risk than are traditional families. For example, Dr. Martin Daly and Dr. Margo Wilson, evolutionary psychologists at McMaster University in Hamilton, Ontario, found that the rate of infanticide is 60 times as high and sexual abuse is about eight times as high in step-families than it is in biologically related families.
"We demonstrated a very large excess risk to stepchildren, an increase of thousands of percentage points," Daly said in an interview.
The matter is especially pressing now when rates of divorce and remarriage are at an all-time high.
Traditional sociological explanations for abuse and conflict in step-families have focused on issues like economic stress, low socioeconomic status and emotional instability. But evolutionists say these are only proximate, not ultimate, causes of the difficulties that sometimes arise in step-families. The underlying trigger, the evolutionists believe, lies within our inherently selfish genes, which are biologically driven to perpetuate themselves. Genetically speaking, step-parents have less of an investment in unrelated offspring and may even regard them as detrimental to their chances of passing along their own genes, through their own biological children.
Citing examples among animals -- from birds and bees to lions and baboons -- that share our propensity to live in family groups, the evolutionists maintain that conflicts and incestuous relations are more common among step-parents and stepchildren and among children and their half-siblings and step-siblings because they are less closely related to one another than are parents and children in a traditional family. In fact, Drs. Daly and Wilson found that when degree of genetic relatedness is taken into account, the role that economic stress plays in problems common in step-families becomes almost negligible.
"There's a lot of violence involving step-relatives that can't be explained in terms of poverty, maternal youth and other commonly cited factors," Daly said in an interview.
Dr. Stephen T. Emlen, evolutionary biologist at Cornell University, maintains that a dearth of shared genes is the unconscious force that underlies many of the difficulties encountered in step-families. These problems involve not only conflicts, violence and incest but also guilt and hurt that can result when step-parents do not form a close bond with their spouses' children, with whom they share no genes. Emlen believes that over the course of several million years, the forces of evolution have selected for behaviors within families that foster the perpetuation of the family genes.
Emlen asks, for example, whether men are really so different from, say, male lions; when taking over a new family, the male will kill any offspring still present from the female's prior matings.
In a paper recently published in the journal Social Science Information, he wrote, "Conflicts are intensified in step-families because step-parents are unrelated to offspring of the previous pairing, and extant offspring are less related to future young of the new pairing." Emlen, who has spent 20 years studying animal family systems, says this is as true of Homo sapiens as it is of lower animals that live in family groups, including wolves, mongooses, rodents, scrub jays, bee-eaters, wrens, ants, bees, wasps and termites.
He theorizes that through the process of natural selection, our genes have provided a template for certain behaviors that foster their perpetuation through our biological offspring and prompt us to invest less energy in maintaining a set of genes that is less like our own.
Sociologists tend to reject such intimations of genetic determinism, citing the fact that humans have minds that can override the forces of genetics. They also note the relatively low rates of abuse or other violence in families with adopted children, who share none of their adoptive parents' genes. The evolutionists do not dispute these arguments; rather they say that an awareness of genetic forces can help people overcome them. Emlen suggested that a society cognizant of the inherent genetic risks can find ways to capitalize on the human intellect and head off trouble before it happens. Emlen emphasized that "genes confer only a predisposition, not a destiny."
"Individuals can modify undesirable tendencies once they are aware of them. Modifications of hereditary "decision rules," as Emlen calls them, "are routinely made based on who is watching, the person's social status, kinship, past experience with the individual and the relative age and dominance of the individual."
"I'm not deterministically saying you're going to have problems because you're a step-family," he said in an interview. "There are tons of step-families who are doing absolutely fine." Still, he said it is best to head off trouble by anticipating possible flash points, adding that "it is sometimes very hard to alter things five years down the pike."
"The greatest potential value of the evolutionary perspective is that it tells us when, where and between whom conflict is most likely to occur," Emlen said.
Dr. Michael Kerr, a psychiatrist at the Georgetown Family Center in Washington, who specializes in family problems, praised Emlen's suggestions for defusing potential problems in step-families. "That there should be an evolutionary base to the human family makes complete sense to me," he said, adding "anything that moves society toward a more accurate understanding of what the problems are in families will be helpful in the long run."
Emlen suggested, for example, that single parents considering remarriage emulate female baboons, which do not accept a new male partner unless he demonstrates parenting skills. A new partner entering an existing family "may have to go an extra mile to develop a bond with a stepchild," Emlen said.
He added, "An individual with children should realize the need to look for different traits in a future mate. Qualities such as a demonstrable interest in the children, financial generosity and a willingness to become an active participant in a 'ready-made' family come readily to mind."
A prenuptial step-family agreement might be signed to assure that future step-parents are aware of "the greater statistical risks of conflict, and particularly the greater challenges involved in child rearing, that are associated with reconstituted families," Emlem said. In signing such a document, they "would be acknowledging such risks and accepting their heightened responsibility for dealing with them," he said.
If stepchildren, who share at least half the genes of one parent, are at greater risk than the biological children of both parents, should not adopted children, who are genetically related to neither parent, be at even greater risk?
"Adopted children face nothing like the risk that children in step-families face," Daly said. He and Emlem pointed out that unlike step-parents, both parents of an adopted child want the child and are usually screened by professionals for parental suitability.
In contrast, Daly said, "Many step-parents would really prefer that their spouses' kids had not existed. What often happens in step-families is that the step-parent, who is usually a man, feels exploited, pressured in a direction that his emotions and affections are not pushing him."
He suggested that step-parents "think of their investment in stepchildren as a gift, given out of love for the partner, a part of the web of reciprocity in a remarriage." He concluded that it is better to act like you appreciate making the investment than "to act as if it's your due."
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