SEATTLE , Wash. -- Some of the same evolutionary "predispositions" that held together extended families for our hunter-gatherer ancestors -- and even prototypical nuclear families until recently -- are partly to blame for today's dysfunction, conflict and violence within fractured families, according to a Cornell University biologist who studies heritable adaptations in animal and human societies.
One such ancient, genetically programmed rule -- help your closely related kin -- may have an ugly mirror-face when unrelated individuals become part of the family, Stephen T. Emlen told an American Association for the Advancement of Science (AAAS) session today (Feb. 14) on "Sexual Differences in Mating Strategies: The Interface of Culture, Law and Biology." Just as in many "lower" animals, human stepparents turn a less-caring shoulder -- and occasionally even a violent one -- to children who don't carry their genes, according to Emlen, the Jacob Gould Schurman Professor of Biology at Cornell.
"The good news is we have the potential to largely overcome many of our genetically influenced behavioral predispositions," Emlen said. "With greater awareness and early detection, we can avoid detrimental behaviors," he said, suggesting a renewed role for grandparents and a policy change for government.
Emlen's AAAS presentation, titled "The Evolutionary Study of Human Family Systems," follows his publication of "15 Predictions of Living within Family Groups" (Proceedings of the National Academy of Sciences, Aug. 29, 1995), which explains the evolutionary roots of behaviors ranging from infanticide and sexually related aggression to multigenerational nurturing during hard times.
More than 300 species of birds and 80 kinds of mammals are known to follow two
family-grouping predispositions that keep chip-off-the-old-block DNA in the gene pool -- biparental care of offspring and multigenerational alliances to help raise related young. So did most Homo sapiens until the latter half of the 20th century.
"The helping individual receives indirect genetic benefits in direct proportion to how closely it is related to the recipients of its aid. All else being equal, the closer the kinship, the greater the tendency for animals to cooperate," Emlen said, explaining the so-called kin selection theory (and how the help-your-relatives rule became incorporated into our genetic makeup) in an article prepared for the journal Social Science Information.
Most nonhuman primate species are not useful models of family cooperation, Emlen said, because long-term pair bonds are rare and male primates seldom help care for infants. Among animal species showing heritable tendencies for family organization are the lion; mongoose; marmoset; naked mole-rat, which is studied by Emlen's colleagues at Cornell; scrub jay of Florida and Mexican jay of Arizona; white-fronted bee-eater, which Emlen studied in Africa for more than a decade; and acorn woodpecker. Even the common crow helps parents raise younger siblings.
These heritable adaptations to family living were selectively advantageous for life in ancestral (pre-agricultural, pre-industrial) extended families, Emlen told the AAAS meeting. And most of the rules still worked as nuclear families became the early-20th-century norm and extended families, more of a rarity.
"Now, the nuclear family is becoming less common. It's being replaced by increasing numbers of single-parent and stepparent families. At the same time we are seeing an increase in child abuse, child delinquency and child truancy," Emlen said.
When Emlen surveyed social scientists' reports, he found disturbing correlations between family structure and the well-being of children. Among them:
- Stepchildren suffer much higher rates of physical abuse and even death than children in intact families.
- Stepparents invest less time and effort in the offspring from their partner's previous marriage than they do with their own children.
- Stepchildren are at greater risk for sexual abuse than children in intact families, and stepparents are overwhelmingly the abusers. The incidence of sexual abuse of stepdaughters in one study was eight times that of biological daughters.
- Children in stepfamilies leave home significantly earlier than children in intact families.
- Stepfamilies are less stable than intact families. The incidence of subsequent divorce is higher in second marriages and increases with the number of stepchildren present.
"The rules we evolved with don't work well in the greater diversity of family types present today," Emlen said. "One could ask: 'Who cares about predispositions? After all, we are conscious beings who can deliberately change our behavior when we put our minds to it.' But we don't always have the luxury of reacting rationally in certain situations."
That is where some awareness of our evolutionary legacy can help minimize damage in the "new" social arrangements, the Cornell biologist suggests. Emlen is not prepared to say there is a gene for helping kin or harming others. But the human genome project offers an interesting analogy, he says. Just as the discovery of genes for dispositions to disease enables people to reduce other risks of contracting disease, knowing our behavior predispositions can help us avert social conflict.
"Be aware that if you are in a stepfamily situation -- or if you are a social worker dealing with stepfamilies -- there is a statistically greater chance of problems," Emlen said. "We didn't ask for these biological predispositions; they came with a genetic package that worked for our ancestors for thousands of years. But, armed with knowledge and insight from the evolutionary perspective, we can better identify likely flashpoints of family conflict and use our intellectual resources to consciously suppress those predispositions that negatively impact others."
The biologist also offers a way to turn predispositions to the family's favor: Bring grandparents back into the child-rearing picture, especially in single-parent families. Government agencies, he says, could assist by offering tax incentives to grandparents who directly assist in rearing grandchildren in need and to parents who wish to move closer to their parents, or vice versa.
"All the studies of animal and human societies with extended family arrangements predict that this would work," Emlen said. "Certainly, grandparents of many species, including human, have a predisposition to care for kin."