Kin Investment by Step-Grandparents—More Than Expected

Abstract

Asymmetric grandparental caregiving is usually explained by the paternity certainty hypothesis. Accordingly, the lower investment by grandfathers (GFs) and paternal grandparents, as compared to grandmothers (GMs) and maternal grandparents, is based on differential kinship certainty to grandchildren. Hence, differential caregiving by grandparents is equated with their on-average different genetic relatedness to a grandchild. But what about nonbiological grandparents? All else being equal, step-grandparents should not invest highly in step-grandchildren and their investment should not be asymmetric because no differences in kinship certainty exist. However, coresidence with a biological grandparent might enhance step-grandparents' investment. From a total of 508 respondents from Germany and the USA, 108 were step-grandchildren who reported kin caregiving from 151 stepgrandparents. Further, we analyzed data of 45 stepparents, 1,005 biological parents, and 1,585 biological grandparents. We identified different types of step-grandparents. Subjects reported step-grandparents who were spouses of biological grandparents (Type I) much more often than step-grandparents who were parents of stepparents (Type II). Investment and emotional closeness ratings for step-grandparents were relatively high, however, on average somewhat lower than that of biological grandparents.Step-GFs provided more caregiving than step-GMs for step-grandchildren. More detailed analyses, however, revealed that this applied only for later partners of biological GMs (Type Ib) who were not already stepparents of the parents (Type Ia). Type Ib step-grandparents generally invested less in step-grandchildren than Type Ia; however, Type Ib maternal step-GFs, by contrast, invested more. Similar to step-GFs, stepfathers also invested more than stepmothers. However, this could be explained by the stepfathers' household connection with their stepchildren. We conclude that mating effort best describes the differential stepGFs' step-grandchild investment.

Gift Giving at Israeli Weddings as a Function of Genetic Relatedness and Kinship Certainty

“…Aside from the effect of genetic relatedness on the size of monetary gifts, our study showed that matrilateral investment was greater than patrilateral investment, presumably because of differences in kinship assuredness (for other suggestions, see Pashos, Schwarz, & Bjorklund, ). The link between kinship certainty and investment is well established in evolutionary theory.…”

Do mothers also “manipulate” grandparental care?

“…Several studies have indicated that males, due to paternity uncertainty, should rely more heavily on resemblance to children, as a cue of genetic relatedness, for investment decisions than females ( Daly & Wilson, 1982 ; Alvergne, Faurie & Raymond, 2009 ; Apicella & Marlowe, 2004 ; Platek et al, 2002 ; Burch & Gallup, 2000 ; McLain et al, 2000 ; Heijkoop, Dubas & Van Aken, 2009 ), but few have extended and investigated this prediction regarding grandparental investment (see, however, Euler & Weitzel, 1996 ; Schlee & Kirchengast, 2015 ; Pashos & McBurney, 2008 ). Also, putative relatedness weighted by certainty in relatedness, better predict willingness to invest in kin than putative relatedness alone ( Antfolk et al, 2017 ), and kin selection theory is also supported by studies comparing investments by grandparents and step-grandparents ( Pashos, Schwarz & Bjorklund, 2016 ; Gray & Brogdon, 2017 ). In fitness terms, grandparental investments can be viewed as an extension of parental investment, or as Euler & Weitzel (1996) points out, as a “differentiated subset of parental effort.” Consequently, investment decisions made by grandparents should be subjected to the same scrutiny as paternal investment decisions.…”

Asymmetric Caregiving by Grandparents, Aunts, and Uncles and the Theories of Kin Selection and Paternity Certainty: How Does Evolution Explain Human Behavior Toward Close Relatives?

“…In total, the greatest grandchild investment is, therefore, by the maternal grandmother and the least grandchild investment by the paternal grandfather. This is the result not only of many empirical studies from evolutionary research (Bishop, Meyer, Schmidt, & Gray, 2009;Danielsbacka & Tanskanen, 2012;Danielsbacka, Tanskanen, Jokela, & Rotkirch, 2011;Euler & Weitzel, 1996;Kirchengast & Putz, 2016;Laham, Gonsalkorale, & von Hippel, 2005;Pashos, 2000;Pashos & McBurney, 2008;Pashos, Schwarz, & Bjorklund, 2016;Russell & Wells, 1987;Smith, 1988Smith, , 1991Steinbach & Henke, 1998) but also from the social sciences (Eisenberg, 1988;Hartshorne & Manaster, 1982;Hoffman, 1979Hoffman, /1980Lussier, Deater-Deckard, Dunn, & Davies, 2002;Matthews & Sprey, 1985;Monserud, 2008;Rossi & Rossi, 1990;Uhlenberg & Hammill, 1998;Van Ranst, Verschueren, & Marcoen, 1995). Other research studies, which directed their focus on aunts and uncles instead of grandparents, found a similar asymmetric pattern with highest kin investment by maternal aunts and lowest by paternal uncles (Gaulin, McBurney, & Brakeman-Wartell, 1997;Hoier, Euler, & Hänze, 2001;McBurney, Simon, Gaulin, & Geliebter, 2002;Pashos & McBurney, 2008).…”

“…In a British survey, Dench and Ogg (2002) similarly interpreted stepgrandfathers to be more engaged with their new families compared with stepgrandmothers. In evolutionary terms, the stepgrandfathers' caregiving intention might be best explained by mating effort (Pashos et al, 2016). Good caregiving abilities appear to make men attractive marriage partners.…”