Main Findings of Chapter 4

In this chapter, I investigated whether the negative effects associated with stepfather presence were driven by the reduced quantity and quality of direct investments children receive within the household, or whether stepfather presence led to detrimental effects on child development regardless of direct investments. I specifically explored if stepfather presence effects were driven by 1) levels of maternal direct investments in the household, 2) differences in the levels of stepfather/father direct investments in the household, and 3) differences in the effectiveness of stepfather/father direct investments. Ultimately, this would highlight the role of stepfathers as allomothers in the UK childrearing system. Given the importance of fathers on child development highlighted in Chapter 3, how does an unrelated male as a carer influence child quality in contemporary developed contexts? Firstly, I found no stepfather presence effects on height. It may be that stepfather presence does not affect the physical development of children, but it could be that stepfather effects were not found due to lack of analytical power. The latter scenario is more likely considering our significant findings of father score on children’s height in the previous chapter, which was not replicated in the current series of analyses. Investment effects on height are generally small. In Chapter 3, we saw that a 1 point increase in father score was associated with a 10 to 13 mm reduction in height. In a longitudinal analysis of children from birth to age 10 using ALSPAC, stepfather presence was associated with a change of 8.7mm to 9.9mm in children’s height (Lawson & Mace, 2008). In both cases, a longitudinal approach was taken which allowed for larger sample sizes and more cases, increasing power. Unfortunately, this was not possible in the current study due to household changes which follow longitudinal formats. The problem is in that we cannot simultaneously include information on single mother households, direct investment levels and change in family structure: As there is no information on absent-father investments for single-mother households, there are issues of perfect collinearilty between lack of partner score and single mothers. Without including single mother households, however, we are unable to track change in family structure. Overall, it is likely that the number of stepfathers in our current study was too small to pick up any stepfather effects on height with our cross-sectional approach.

In addition, it is likely that our sample of stepfather households may be slightly different from other studies, in that stepfathers had entered the household at a relatively young age and household structures were stable. Therefore, the negative effect of

p. 124 stepfather presence on child outcomes in this study may be smaller compared to other studies. Combining these two points, it is likely that I was simply unable to capture stepfather effects on height.

In contrast, for school test score and behavioural difficulty score, there was a significant negative effect of stepfather presence in the household. For school test score, the negative effects of stepfather presence was reduced when mother score was added to the model, and the negative effect of stepfather presence was reduced to a greater extent and lost its significance when partner score was added to the model. However, the positive effect of direct investment on children’s educational achievement was the same whether it was provided by the father or stepfather.

This suggests that the negative effect of stepfather presence on children’s educational achievement is primarily due to the lower levels of direct investments children receive within stepfather households. Furthermore, stepfather investment itself has a positive effect, and the negative stepfather effect on educational achievement may be overcome if stepfathers are encouraged to interact more with their stepchildren. This is in contrast to previous literature in developed populations exploring stepfather presence which suggest stepfathers are “bad” for child development. It seems that stepfather presence, independent of investment levels, does not trigger the children to achieve lower levels of cognitive development as would be expected following the ideas proposed by Belsky, Steinberg & Draper (1991). In fact, the current results suggest that stepfather direct investments can lead to greater child quality regarding cognitive development. These findings in ALSPAC differ from that of Lawson & Mace (2009b), where they found that stepfather presence had no significant effect on educational achievement at age 4/5 yrs. and 6/7 yrs. However, I believe this difference is driven by sample size. Lawson & Mace (2009b) took a cross-sectional approach as I have here, but did not impute missing values. This left their analyses with a comparatively smaller sample size (N=3762 for 4/5 yrs., N=4638 for 6/7yrs), potentially leading to lack of power through small numbers of stepfathers and less accurate estimates.

Secondly, for behavioural difficulty score, the negative effect of stepfather presence was not affected when mother score was added to the model. However, the negative effect of stepfather presence was reduced when partner score was added to the model, suggesting differences in investments between fathers and stepfathers partly drive the stepfather effect. Furthermore, direct investments provided by stepfathers had no beneficial effect on children’s behavioural difficulty score. Overall, this suggests that the negative effect of stepfather presence on children’s socio-emotional development is due to multiple factors:

p. 125 First, unlike paternal direct investments, children’s behaviour is unlikely to improve however much stepfathers invest in children. This could suggest that paternal direct investments may not be substitutable with stepfather investments for children’s socio- emotional development. Reduced paternal investments, combined with the ineffectiveness of stepfather investments, are both likely to contribute to the higher levels of behavioural difficulties for children in stepfather households. Unlike with school test score, this suggests that the negative effect of stepfather presence on children’s socio- emotional development is unlikely to be overcome even if stepfathers are encouraged to interact more with their stepchildren.

Second, stepfather presence was associated with detrimental effects on children’s behavioural difficulties irrespective of within-household direct investment levels. Note that this does not necessarily mean stepfathers directly cause negative effects on children’s socio-emotional development. While I took steps to minimise unobserved heterogeneity, stepfather households are inherently associated with greater family disruption which could be contributing to the detrimental effects. Overall, what these results suggest is that stepfather presence is associated with detrimental effects on children’s behaviour, independent of the quality and quantity of direct investments within the household. This result is in line with Belskey, Steinberg & Draper (1991), where stepfather presence and the associated household instability may serve as a cue of environmental instability for children, prompting them to take a faster life history approach in terms of socio-emotional development.

The aim of the chapter was to disentangle the mechanism behind stepfather effects on child development. Previous studies have shown that stepfather presence is detrimental to child quality, while at the same time studies shows stepfathers do provide investments to their unrelated children. This lead to the question, why are stepfathers having negative effects even when children are receiving investments from an extra adult? Overall, the current results suggest that the mechanism behind the “negative stepfather effects” on child development may be outcome specific: Children’s cognitive development is influenced by the reduced direct investments in stepfather households, while children’s socio-emotional development is influenced by the lack of paternal investments as well as factors related to stepfather presence itself. While this chapter does not address why these differences exist, it may be that children’s socio-emotional development is more susceptible to cues of environmental instability (e.g., stepfather presence) compared to cognitive development. This could be an adaptive mechanism if lower levels of socio- emotional development encourages faster life history strategies such as earlier age at

p. 126 reproductive maturation and greater risk-taking. Ellis et al. (2003) has found that father absence in the U.S. and New Zealand is associated with internalising and externalising problems as well as early sexual activity and pregnancy in girls, though the causality between behavioural difficulties and sexual risk-taking is unclear in this particular study. However, another study from New Zealand suggests that conduct problems leads to adolescents engaging in risk-taking behaviours such as risky sexual behaviour and substance use (Fergusson & Woodward, 2000), suggesting that lower socio-emotional development may indeed encourage faster life history strategies.

The findings from the chapter suggests that stepfathers could have a positive impact for some aspects of child quality through their direct investments. However, given that stepfather investments are thought to predominantly serve as mating effort, it would be unusual for stepfathers to invest as much as fathers who have the added incentive of parenting effort. Furthermore, stepfather investments for some aspects of child quality may have negligible effects. From the child’s perspective, this suggests that having a stepfather as an allomother may not necessarily be beneficial regarding child quality/embodied capital. However, stepfathers may be an important addition for mothers regarding their future reproductive output. Stepfather households may be a case where mothers “win” in the parent-offspring conflict, where an allomother enters the household not to improve investments into current offspring, but as investments towards future offspring.

4.4.2 Limitations of the Current Analyses

In the current study, I tried to minimise confounds related to stepfather presence with the sample selection criteria which required that households were stable, and that stepfathers entered the household at a very young age. Furthermore, I included a wide range of controls in attempt to minimise such problems. Nonetheless, there is the possibility that our findings could be driven by other unexplored characteristics specifically associated with stepfather households. In particular, one aspect I was unable to explore was the effect of absent fathers on child development, which may influence or interact with stepfather presence.

Unfortunately, detailed information on investments by absent fathers is unavailable in ALSPAC. Furthermore, there are methodological issues with perfect correlation between stepfather presence and father absence, meaning the effect of absent fathers cannot be analysed within the current framework where stepfather effects are compared against

p. 127 father-present households. Stepfather presence is usually met with the reduction in the involvement by non-resident fathers (Furstenberg, Morgan & Allison, 1987; Christensen & Rettig, 1996; Juby et al., 2007), whose investment levels are already significantly lower than live-in fathers (Anderson, Kaplan & Lancaster. 1999a, 1999b; Gibson-Davis, 2008). It may be that the negative effect of stepfather presence on behavioural difficulties (controlling for maternal and stepfather direct investments) is driven by the lack of investments by absent fathers. If so, this would complement my suggestion that paternal direct investments may not be substitutable for children’s socio-emotional development.

There is also a possibility that the effects attributed to the levels of stepfather investments may in fact be due to correlated levels of paternal investment from non- resident fathers. Recent studies suggest that there is no correlation between stepfather involvement and absent-father involvement within stepfather households (e.g., Jensen & Shafer, 2013; King, Thorsen & Amato, 2014), while others have found that contact with non-resident fathers negatively correlate with the quality of stepfather-child relationships (e.g., MacDonald & Demaris, 2002). If the effects of stepfather investments are driven by the negative correlation with absent-father investments, we would expect high stepfather investments to have no, or even a negative, effect on child outcomes. In fact, I found the opposite result on educational achievement where stepfather investments were associated with a positive effect on test scores. Thus, it is unlikely that the effect of stepfather investments on educational attainment is driven by absent-father investments. In contrast, absent-father investments could be an important factor for behavioural difficulty, as stepfather investments were found to be ineffective. If so, this complements my suggestion that paternal direct investments may be particularly important for children’s socio-emotional development. For future studies, it would be interesting to investigate if and how stepfather presence effects are affected by absent fathers.

One unaddressed issue, especially relevant if stepfather investments exist as mating effort, is the impact of sibling competition. While I control for additional births which include half-siblings from stepfathers, whether the impact of stepfathers differ after the birth of a half-sibling has not been explored. Lawson & Mace (2009), using similar ALSPAC data, have shown that each additional sibling leads to lower levels of direct parenting per child. Under HBE, we would expect stepfather parenting for focal children to decrease with a birth of a half-sibling even more than expected in paternal parenting, as stepfathers have a greater incentive to invest in their biological child. In stepfather households, focal children may lose out a greater proportion of direct investments to half-siblings. While I control for investment levels the focal child receives, which should partially address the

p. 128 issue of half-siblings, this sibling competition could impact focal children in other ways. For instance, the quality of stepfather parenting, not captured in the current parenting scores, could decrease as stepfathers have less incentive to provide high quality direct investments. A greater level of sibling competition may serve as a cue of environmental harshness, which may encourage children to follow a faster life history strategy. This could mean that the “negative” effect of stepfather presence may be greater and stepfather direct investments less effective in stepfather households with half-siblings.

Finally, it is important to note that our current sample of stepfather households is unusual in that stepfathers entered the household when children were very young, with household stability across time-points. While this allowed us to compare father and stepfather households, the negative effects on child outcomes associated with stepfather presence may be underestimated compared to the wider population. However, some academics suggest that early family disruption (between birth and age 7), has the greatest impact on child outcomes, potentially capturing children during their critical period of development regarding the adjustment of life history trajectory (Draper & Harpending, 1988; Belsky, Steinberg & Draper, 1991; Ellis et al., 2003). In the U.S. and New Zealand, father absence before age 5 had the greatest impact on girls’ sexual maturity, where father absence in the first few years of life was associated with earlier sexual activity and pregnancy. If so, we are still likely to capture the impact of stepfather presence as an environmental cue of instability within the current analyses.