Offspring fertility and grandchild survival enhanced by maternal grandmothers in a pre-industrial human society.

摘要: Help is directed towards kin in many cooperative species, but its nature and intensity can vary by context. Humans are one of few species which grandmothers invest grandchildren, this may have served as an important driver our unusual life history. But helping behaviour hardly uniform, insight into the importance grandmothering human evolution depends on understanding contextual expression benefits. Here, we use eighteenth-nineteenth century pre-industrial genealogical dataset from Finland to investigate whether maternal or paternal grandmother presence (lineage relative focal individuals) differentially affects two key fitness outcomes descendants: fertility survival. We found shortened spacing between births, particularly at younger mother ages earlier birth orders. Maternal increased likelihood grandchild survival, regardless had grandchildren only through daughters, sons, both. In contrast, was not associated with descendants' discuss these results terms current hypotheses for lineage differences outcomes.