“Not all grandparents invest the same time and resources in their grandchildren,” says UNSW psychologist and study co-author, Dr Bill von Hippel.
“Maternal grandmothers are closer to their grandchildren than other grandparents. The next closest relationship between grandparents and grandchildren is by maternal grandfathers, then paternal grandmothers and, last of all, paternal grandfathers.”
To be published in Personality & Social Psychology, the study is the first to confirm that preferential investment stems from genetic uncertainty. The finding is based on data from 780 university students who rated their emotional closeness to each biological grandparent from zero (cold or negative feelings) to 100 (warm or positive feelings).
“Not all grandparents are certain that their grandchildren are their own,” says von Hippel. “A woman always knows she is the mother of her child but a man has a some uncertainty about his paternity because he might have been cuckolded,” he says.
“This issue is compounded for grandparents. A maternal grandmother knows with certainty that her genetic material has passed to her grandchildren through her daughter but a paternal grandfather has double uncertainty -- he has no certainty that either his son or his grandchildren bear his genetic material.”
Maternal grandmothers and paternal grandfathers represent two extremes of this genetic uncertainty spectrum says von Hippel.