CHICAGO (AFP) - Forget radical calorie restriction or human growth hormone. If it's longevity you are after, you may want to consider spending more time with members of the younger generation, according to an animal study. The study was done in fruit flies and builds on earlier research showing that interaction with younger members of the species appears to be a factor in healthy aging, both in humans and animals. For the experiment, researchers raised members of a mutant, short-lived species of fruit fly, (Sod flies) in a vial with younger members of control fruit flies. They also paired older mutant fruit flies with younger mutant flies in separate vials. They found that the mutant flies raised with the younger control flies lived twice as long as mutants housed with other mutants. Subsequent testing also showed that the mutants housed with their younger, longer-lived relatives had improved physical responses and better survived environmental stresses compared to fruit flies that remained among the mutant population. The results show that social interaction with younger members of the species confers physiological benefits at least in mutant fruit flies, said lead author of the paper, Chun-Fang Wu, professor of biology at the University of Iowa. It's not clear from this experiment what the mechanism of action is. Wu speculated that the social interaction with younger flies could have helped the mutant flies make some kind of physiological adaptation that compensated for the genetic defect that makes the insect particularly vulnerable to oxidative-stress induced aging. The missing link could have implications for human health since the enzymatic mutation in the insect's genetic code mirrors deficits in a number of age-dependent diseases in humans including Parkinson's, Huntington's and Alzheimer's disease. "This study shows that the lifespan of Sod flies is plastic and can be conditioned by social interactions, corroborating the enduring notion that human patients of certain age-dependent neurological diseases may be benefited by an appropriate social environment," the authors wrote. The study appears in the Proceedings of the National Academy of Sciences.