Grandmothers play a crucial role in families enhancing grandchild
wellbeing and survival but their effects can be context-dependent, and
the children born in poor conditions are most likely to benefit from the
investments made by helping grandmothers. In this study, we examined,
for the first time, whether grandmothers' presence modified associations
between adverse birth status and survival up to 5 years of age. In
detail, we verified, whether (i) firstborns, (ii) twins, (iii) children born within 24 months after their sibling, and (iv)
children followed by short interval (i.e. their younger sibling was
born within 24 months) survived better when either their maternal,
paternal, or both grandmothers were present. Moreover, we evaluated
whether illegitimate children survived better when the maternal
grandmother was present. We used an extensive and largely pre-industrial
demographic dataset collected from parish population registers kept by
the Lutheran Church of Finland from years 1730–1895. We show that
although grandmother presence cannot mitigate adverse effects of many
poorer birth conditions, grandchildren whose next sibling was born after
a short interval survived better when the maternal grandmother was
present. Taken together, these findings highlight an important role of
grandmothers in compensating the mother's investment in the new baby,
thus enabling overall faster successful reproductive rate of mothers.
Whilst the opportunity for grandmothers to mitigate the risks of adverse
birth statuses is limited, this study does show - through the
beneficial effect on survival for those with a short subsequent birth
interval - that grandmothers can increase their daughters' and their own
reproductive success.