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Moms with a specific gene variation are more likely to shout at or hit their children when the economy is sour, according to new research.

Moms with a specific gene variation are more likely to shout at or hit their children when the economy is sour, according to new research published in the journal Proceedings of the National Academy of Sciences. Those same moms are less likely to be harsh as the economy improves.

It's not just personal financial stress that sets moms on edge, according to researchers at New York University, Columbia University, Princeton University and Pennsylvania State University, who collaborated on the study.

"It's commonly thought that economic hardship within families leads to stress which, in turn, leads to deterioration of parenting quality," said Dohoon Lee, an assistant professor of sociology at NYU and lead author, in a written statement. "But these findings show that an economic downturn in the larger community can adversely affect parenting — regardless of the conditions individual families face."

The harsh parenting deepened alongside worsening economic conditions solely for moms who had a "sensitive" allele or variation of a specific gene that controls dopamine synthesis. Dopamine is a brain chemical that regulates behavior, the researchers said.

That those moms were less likely to be harsh as conditions improved "provides further evidence in favor of the orchid-dandelion hypothesis that humans with sensitive genes, like orchids, wilt or die in poor environments, but flourish in rich environments, whereas dandelions survive in poor and rich environments," said Irwin Garfinkel, paper co-author and a professor of contemporary urban problems at Columbia's School of Social Work.

"You have the same genes, and with a different environment it's a completely different story," Garfinkel told NPR. "I think that's the most amazing part of what we found."

Scientists used to think the brain cells responded to rewards such as good news, a Brown neuroscientist, Michael Frank, told NPR. "It's now known that they don't react to rewards per se. (Brain cells) increase their level of activity when the outcomes are better than expected and they decrease when the outcomes are worse than expected."

The study was based on data from the Fragile Families and Child Wellbeing Study, conducted by researchers at Princeton and Columbia who looked at families of close to 5,000 children born between 1998 and 2000 in 20 large American cities. Moms were interviewed after the child's birth and again when the child was 1, 3, 5 and 9 years old. They collected the data on harsh parenting at ages 3, 5 and 9. Also at the 9-year point, they collected saliva DNA samples from 2,600 of the moms, and children contributed saliva DNA samples.

For each 10 percent increase in area unemployment, women with the variation reported 2.3 more harsh parenting behaviors, while mothers in general reported 1.6 times more, according to a story in The Australian.

To determine harsh parenting, the researchers looked at 10 measures from shouting and threatening to punishment methods. Researchers also looked at economic conditions in the cities where the moms lived, including unemployment rates and consumer sentiment measures.

They controlled for race, age, immigration status, education level, poverty, family structure, child gender and age.

"It is in the anticipation of the adversity — fear of losing one's job due to deteriorating economic conditions — that is the more important determinant of harsh parenting than poor economic conditions or even actual economic hardship a family faces," the researchers said.

"People can adjust to difficult circumstances once they know what to expect, whereas fear or uncertainty about the future is more difficult to deal with," said Sara McLanahan, co-author and Princeton professor of sociology and public affairs.

Earlier research had shown that having such a gene variation made mothers more likely to show reactive aggression than other mothers.

This study, the authors said, shows "the effect of genes on people's behavior may depend on the quality of their environment."

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