The biology of grandmaternal love

Grandmothers are important alloparents in many human families. According to one prominent hypothesis, the inclusive fitness benefits of grandmaternal caregiving selected for an extension of the human female lifespan up to decades beyond the cessation of reproduction – a developmental stage that is unique among primates. Beyond this extension of the lifespan, it is possible that grandmothers harbor other biological adaptations that prepare them for a special role in caregiving. In this talk, I present evidence from our lab showing that grandmothers have less DNA methylation of the gene that codes for the oxytocin receptor (OXTR) compared with non-grandmother control participants, and grandmothers with less OXTR DNA methylation tend to report more positive feelings between them and their grandchild. In addition, structural MRI brain scans show that grandmothers have a lower brain age compared with controls, and brain age tends to be lower among those grandmothers who report being more positively engaged with their grandchild.  Given known neuroprotective effects of oxytocin, these results raise the possibility that the transition to grandmotherhood involves increases in oxytocin signaling that both facilitate grandmaternal bonding and attachment, and slow brain aging.