Biological grandparents are more likely to invest in their grandchildren on a regular basis than non-biological grandparents, an Edith Cowan University (ECU) study has found.
The study, published in PLOS ONE, is the first to examine the impact of biological relatedness on Grandparental Investment (GPI) in contemporary westernised nations.
GPI, measured as the frequency of informal childcare given by grandparents, was found using Data from the Survey of Health, Ageing and Retirement in Europe in people over the age of 50.
Lead author and ECU School of Medical Sciences senior lecturer David Coall found around 50 per cent of grandparents in Europe invest in their grandchildren, with GPI strongest in grandparents who were directly related to their grandkids.
"For almost weekly childcare, being a biological grandparent was the strongest predictor of GPI," Dr Coall says.
"For the more intensive, almost daily GPI, it was the fourth strongest factor after filial [grandparent-parent] expectations, whether the grandparent has a partner, and if the [parent] was employed."
Dr Coall says non-biological grandparents were more likely to invest at lower levels (almost monthly or less often).
He says non-biological grandparents still invest, but their GPI is not as frequent, with several factors being associated with reasons for reduced investment.
"We found non-biological grandparents live further away, have more children and grandchildren and may feel a lower obligation to some parts of their family," he says.
Further studies are required to examine why, but the paper notes that non-biological grandparents still play a pivotal part in a child's upbringing.
"Evidence is mounting that participating in a caring relationship with a grandparent can be beneficial for the development of grandchildren," Dr Coall says.
"We felt it was crucial to establish what factors were associated with grandparents being involved in their grandchildren's lives.
"Studies from psychology, economics, sociology and evolutionary biology have examined this question, but this is the most extensive international study of GPI."
Dr Coall says it's essential that studies into grandparental and grandchild relationships are conducted, because of the positive influence grandparents can have on child development.
"We are not suggesting all grandparents must invest in their grandchildren … but when a grandparent can be involved in a grandchild's life it does appear to be beneficial especially for psychosocial and emotional development."
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The study is available online: www.ncbi.nlm.nih.gov/pmc/articles/PMC3885520/