Grandmother hypothesis

An explanation of the post- menopausal life stage of human females whereby the existence of grandmothers serves as a biological and social adaptive advantage for humans. Post-reproductive life stages are non-existent among non-human primates, so it is hypothesized that humans evolved to have grandmothers and grandmothering to have individuals who are free to invest their energy into the offspring of their children. This off-loads the reproductive cost of parenting through social kin-networking, and off-set the resource cost of brain- building as parents are freed to provision resources. Increased resource procurement may reduce the inter-birth interval by allowing for earlier weening, which in turn increases offspring production potential, passes down generational knowledge, and increase social networks. In doing so, the grandmother ensures the survival of her genes in subsequent generations. The extended post-reproduction life stage of grandmothers likely had the added output of producing grandfathers, who also provide benefits to the extended family, as well as their own extended reproductive time line that competes with subsequent generations.