A ‘gendered need’ explanation does not fully explain lineage based differences in grandparental investment found in a large British cohort study

Ghysels (2012) argues for a ‘gendered need’ explanation of lineage based differences in grandparental investment. Maternal grandmothers are subsidiary care-givers: only if mothers fail to fulfil this gender role, (maternal) grandmothers will step in. The SHARE data do indeed seem to support this explanation (though see Appendix). However, it is not at odds with an evolutionary explanation, such as paternity uncertainty theory. Paternity uncertainty theory suggests that matrilineal biases will emerge all else being equal (see Euler & Michalski, 2008, for review). If there are differences in need, then all else is not equal, and we should expect grandparents to respond accordingly.