Nathalie ANGIER, Scientists Explore A Grandma Factor. A Crone no more. Grandmothers, once reviled as an impediment to "real research", are increasingley seen as a rich source for understanding aspects of human evolution and behavior. Researchers say maternal grandmothers seem to exert a more beneficial effect than the father's mother, but they differ over the reasons. Some cite the evolutionary influence of paternity uncertainty; mothers are simply more likely to ask their own mothers for help with the children. A study of families in South Asia found that the presence of a paternal or maternal grandmother increased a young woman's overall fertility rate. A recent study of African families found that the presence of the maternal grandmother cut children's chances of dying in half. The presence of the paternal grandmother or of the father, made little difference. For a growing number of evolutionary biologiste and cultural anthropologists, grandmothers represent a key to understanding human prehistory, and the particulars of why we are as we are - slow to grow up and start breeding but remarkably fruitful once we get there, empathetic and generous as animals go, and family-focused to a degree hardly seen elsewhere in the primate order. As a result, biologists, evolutionary anthropologists, sociologists and demographers are starting to pay more attention to grandmothers: what they did in the past, whether and how they made a difference to their families' welfare, and what they are up to now in a sampling of cultures around the world. At a recent international conference - the first devoted to grandmothers - researchers concluded with something approaching a consensus that grandmothers in particular, and elder female kin in general, have been an underrated source of power and sway in our evolutionary heritage. Grandmothers, they said, are in a distinctive evolutionary category. They are no longer reproductively active themselves, as older males may struggle to be, but they often have many hearty years ahead of them; and as the existence of substantial proportions of older adults among even the most "primitive" cultures indicates, such durability is nothing new. If, over the span of human evolution, postmenopausal women have not been using their stalwart bodies for bearing babies, they very likely have been directing their considerable energies elsewhere. It turns out that there is a reason children are perpetually yearning for the flour-dusted, mythical figure called grandma or granny or grand-mère or oma or abuelita. As a number of participants at the conference demonstrated, the presence or absence of a grandmother often spelled the difference in traditional subsistence cultures between life or death for the grandchildren. In fact, having a grandmother around sometimes improved a child's prospects to a far greater extent than did the presence of a father. Dr- Ruth Mace and Dr- Rebecca Sear of the department of anthropology at University College in London analyzed demographic information from rural Gambia that was collected from 1950 to 1974, when child mortality rates in the area were so high that even minor discrepancies in care could be all too readily tallied. The anthropologists found that for Gambian toddlers, weaned from the protective balm of breast milk but not yet possessing strength and immune vigor of their own, the presence of a grandmother cut their chances of dying in half. "The surprising result to us was that if the father was alive or dead didn't matter," Dr- Mate said in a telephone interview. "If the grandmother dies, you notice it; if the father does, you don't." Importantly, this beneficent granny effect derived only from maternal grandmothers - the mother of one's mother. The paternal grandmothers made no difference to a child's outcome. Dr- Donna Leonetti, an anthropologist at the University of Washington and her colleague Dr- Dilip C- Nath presented similar results from their study of two contemporary ethnic groups in northeast India, one Bengali, the other Khasi. In a couple of studies, the divergent effects of the two grandmother species is so pronounced that the son's mother appears not merely a neutral influence on her grandchildren, but a negative one. Dr- Cheryl Jamison, an anthropologist at Indiana University in Bloomington, and her colleagues combed through an exceptionally complete population register from a village in central Japan. The records covered a period from 1671 to 1871. Dr- Jamison and her co-workers determined that when a maternal grandmother lived in the household, boys were 52 percent less likely to die in childhood than if there was no grandmother present. Conversely, when the father's mother lived in the house, boys were 62 percent more likely to die than were those without a resident grandma. For girls, no statistically significant benefit or decrement could be seen from grandmothers of either bloodline. Dr- Jamison cautioned that not too much could be made of the results, for, in a patrilineal culture like that of premodern Japan; where sons were the ones who took in their aging parents, the sample size for maternal grandmothers living with their grandchildren was extremely small compared with that of co-residing paternal grandparents and young children. Nevertheless, she said, she was startled by her results. Those researchers with a Darwinian bent propose that the discrepant effects of maternal versus paternal grandparents is a result of the old evolutionary bugaboo, paternity uncertainty. Maternal grandmothers, they reason, are confident that the grandchildren in question are their blood relations, and hence worth working for, whereas the mother of a son, ever unsure of ber daughter-in-law's fidelity, may withhold her love and care, albeit unconsciously, from the children before her. Others are less quick to pin everything on biology, and offer another explanation or the comparatively salubrious effects of a maternal grandmother. Mothers overwhelmingly are the designated caretakers of children, they say, and when children need help, whose name are they going to call? Mom-my! "It's to be expected that a woman would turn to the person she knows best for help with the children, and that person is much likelier to be her mother than ber mother-in-law," said Dr- Martin Kohli, director of the Research Group on Aging and the Life Course at the Free University of Berlin. "And so it is that the maternal lineage bas the opportunity to make a difference."