Among the major challenges the world is facing is the problem of global environmental change. Experts estimate that, if nothing is being done, by 2052, the earth temperature is likely to rise by 1.5 °C above pre-industrial levels [1
]. Such an increase in temperature will probably have devastating ecological and social effects, the costs of which will be carried by future generations. Over the past few years, these future generations—our children and grandchildren—have come out in massive numbers to make a stance against climate change and persuade governments and industry to take appropriate action to promote sustainability. For example, on 20 September 2019, more than 4 million schoolchildren participated in demonstrations worldwide to demand political action for a better climate [2
]. Are these attempts effective? Are governments and the people who vote for them persuaded by appeals about the welfare of their children and grandchildren? This research examines the effectiveness of children-based appeals in persuading people to behave more sustainably.
One of the main obstacles to sustainable behavioral change is that many environmental problems are social dilemmas [3
]. Social dilemmas are known in the social sciences as situations in which people manage conflicts between their immediate personal interests and long-term collective interests [4
]. Although claiming extra resources for oneself is the rational thing to do, such selfish actions constitute a problem for the collective in the long term [5
]. In social dilemmas, the common pool is only maintained if individuals show restraint [7
]. The classic story of the tragedy of the commons serves as a metaphor for these types of problems [8
]. This parable depicts how a small pasture shared by multiple herders is devastated because, despite the fact that every herder wants to maintain suitable pasture levels for the survival of their cattle, they each realize that by just adding some more animals to the pasture, they could receive more profit at the expense of their peers; thus, leading the pasture to overexploitation. Although Hardin [8
] proposed that the only alternative to avoid devastation of the commons is jointly agreed coercion, exercised through institutions responsible for managing the commons, an evolutionary framework predicts that, in certain circumstances, people can behave in a cooperative and altruistic manner especially if their long-term genetic interests are highlighted [9
1.1. Kin Selection Theory
Studying environmental dilemmas from an evolutionary psychology perspective may give some insights for environmental policymaking [3
]. Evolutionary perspectives on human decision-making suggest that there are several ways out of the commons tragedy. Studies on human cooperation have emphasized the role of punishment [11
], reciprocity [12
], and reputation [13
] in promoting cooperation for the environment. However, a crucial, additional factor to consider is the role of kinship. Hamilton [9
] defined inclusive fitness as a mathematical rule which posits that an organism will behave in an altruist fashion if such behavior increases the fitness of others who share the organism’s genetic makeup. According to this rule, an actor will be altruistic only if the product of the recipient’s benefits derived by the actor’s altruist act (B) and the genetic relatedness between the two of them (r) exceeds the cost of behaving in an altruistic manner for the actor (C); the rule thus can be expressed as rB > C.
Indirect fitness through relatives is often referred to as kin selection. Kin selection theory asserts that humans are predisposed to ensure the survival and replication of their genes which they share with kin including their children [15
]. A child shares 50% of their genes with a sibling as well as with each biological parent, and children share 25% with each of their grandparents. Animal behavior studies provide much support for Hamilton’s rule [16
]. As the relatedness within the group varies, individuals cooperate more with those that share more of their genes [18
]. Psychological research shows that in hypothetical life-and-death situations, people are more likely to help members of their close family, compared to more distant kin [20
]. Moreover, because perceptions about genetic relatedness are not error free, people also cooperate more with individuals that they share a physical resemblance with, like facial similarity [21
1.2. Can Kin Appeals Save the Environment?
Following the logic of kin selection, we propose that, in environmental campaigns, a reminder of kinship—an appeal to the welfare of one’s kin, especially their biological children—may encourage pro-environmental intentions [10
]. Indeed, previous work has shown that in resource dilemmas, a cue of kinship prevents the commons tragedy described by Hardin [8
] by promoting collective restraint. Krupp, Debruine, and Barclay [21
] reported the results of a public goods game in which participants played against ostensible participants who varied in their degree of facial resemblance with the actual participant. As expected from a kin selection perspective, public good contributions increased as the facial resemblance between group members increased.
Although kin selection theory predicts environmental cooperation among all kinds of close genetic relatives, here, we focused on parents and children specifically. Some lines of research in environmental psychology and environmental demographics are consistent with the idea that people with children care more about the future of the planet. For instance, previous research has shown that people with larger families tend to have more environmental knowledge and more positive attitudes towards environmental quality [22
], and that parents, compared to non-parents, are willing to pay more for environmental goods improvement [23
]. Also, other work has indicated that married women parenting at least one child are more willing to pay for an environmentally friendly product than women who are not yet mothers [24
]. Similarly, Loureiro et al. [25
] showed that being female and having children in the household increased the willingness to pay for eco-labeled apples. Furthermore, using hypothetical children-based appeals, Van de Vyver et al. [26
] showed reduced engine idling at long wait stops among car drivers. This finding is consistent with recent research on animal conservation showing that kinship appeals increase conservation efforts for a fictitious endangered animal, compared to anthropomorphic appeals, where the species was framed as a metaphor of a non-genetically related human [27
]. Also, unpublished work by Neufeld et al. [28
] has shown that the use of kin-based appeals stressing the welfare of potential children enhances people’s self-reported willingness to perform pro-environmental behaviors.
Yet, not all studies have found consistent results on this matter. Fisher et al. [29
] found that having one or two children increased the likelihood of recyclable bag use but no other environmentally friendly behaviors. Thomas et al. [30
], using longitudinal data representative of the UK population, failed to find evidence that having a newborn increases parents’ self-reported environmental attitudes and behavior. Instead, the authors reported that having a newborn led to a small decrease in the frequency of three (out of fourteen) pro-environmental behaviors such as car-sharing and the use of public transport as alternatives to the use of personal automobiles. A potential reason for these inconclusive findings is that certain contextual factors might obscure the effect of children-based appeals on environmental outcomes. As pointed out by several authors (e.g., [26
]), an increase in family size (e.g., having a newborn) might increase pro-environmental concerns, but at the same time might produce a less environmentally friendly lifestyle temporarily due to the fact of, for instance, financial concerns, safety issues, or time constraints. Indeed, previous research shows that an association between parenthood and being worried about the consequences of climate change emerges only when emotional aspects of the risk are measured but not when parents are just required to conduct cognitive-based estimates of the risk [31
]. It is thus important to focus more on the psychological mechanisms involved in environmental decision-making in family relations.
1.3. Parental Care
Following the logic of kin selection theory, environmental intentions may be fostered by a parental care motivation which, in turn, may be influenced more distally by the salience of having children. The fundamental motives framework asserts that the pursuit of different fundamental motives (e.g., for protection, parenting, status) leads humans to behave in ways that maximize their survival and reproductive success [32
]. Parental care motivation activates people’s concerns about family members and triggers behavior that is aligned with people’s genetic interests. This evolutionary-based framework indicates that certain aspects of the many different situations humans commonly encounter in their daily life act as cues that temporarily
activate one or various fundamental motives guiding social behavior [34
]. For instance, a crying baby may signal to parents that their offspring is in danger and, therefore, increase their parental care motivation which should then evoke nurturing and protection behavior among parents. Similarly, exposure to cues that indicate that someone is a parent might increase their parental care motivation towards their children, and this may activate greater concerns and intentions to save the environment, thereby saving their genetic future.
In this investigation, we tested, in four separate studies, whether children-based appeals influence people’s pro-environmental intentions through increased parental care motivation. As previous evidence on the direct link between children-cues and pro-environmental outcomes is mixed, here, the main focus was on the potential indirect effect of children-based appeals on environmental outcomes through increased parental care motivation. (Recent literature on path analysis and mediation argues that there is no need for a significant relation between the independent and dependent variables to have an indirect effect [35
]. Indeed, as long as there is a significant a × b effect, mediation has occurred [36
]). We explored this effect on two different environmental outcomes: environmental behavioral intentions (e.g., collecting and recycling used paper) and environmental altruistic intentions (e.g., donating money to and volunteering for an environmental charity). We hypothesized that an appeal to the welfare of one’s (potential) children increases the motivation for parental care which, in turn, positively predicts environmental behavioral intentions and environmental altruistic intentions.
6. Additional Analyses
Across four studies, our findings show a stable positive indirect effect of children-based appeals on environmental behavioral intentions. In these studies, we focused on the unique effect of a cue of having children on environmental outcomes; therefore, we decided to statistically control for potentially influencing factors derived from the participants’ life history such as sex, age, and parenthood status. Given that previous research has shown that parents have a higher parental care [36
], one way to triangulate our findings was to evaluate the effect of actual parenthood status. To test this, we used the samples of Studies 1–4 to conduct a meta-analysis of the effects of parenthood status on environmental behavioral and altruistic measures. As the studies were not identical, we considered random effects to be an appropriate meta-analytic procedure. Fifteen correlation coefficients across the four studies were analyzed. Overall, compared to non-parents, parents showed greater environmental behavioral and altruistic intentions, r
= 0.089 (since this effect size was small, we tested whether it was equivalent to 0 [61
]. Given the bounds (−0.10, 10) and α = 0.05, the TOSTmeta analysis showed that d
= 0.191 (i.e., r
= 0.089) was statistically different from zero and statistically not equivalent to 0 (Z
= 5.29, p
< 0.001; Z
= 1.65, p
= 0.951); thus, it cannot be considered trivial), 95% CI (0.035, 0.143), and the correlations were homogenous, χ2
(3) = 1.605, p
= 0.658. Moreover, 0% of the variance in effect-sizes can be explained by the differences among studies. This effect was not moderated by the type of outcome being predicted (i.e., environmental behavioral intentions, donations, and volunteering), χ2
(3) = 1.624, p
Similarly, a second meta-analysis (k = 4) showed that parental care was positively associated with being a parent, r = 0.345, 95% CI (0.263, 0.422), and correlations were not homogenous, χ2 (3) = 8.294, p = 0.040. Approximately 64% of the variance in effect-sizes could be explained by the differences among studies which is a relatively modest percentage.
7. General Discussion
Based on the kin selection perspective [15
] and the fundamental motives framework [33
], we hypothesized that an appeal to the welfare of one’s children would stimulate pro-environmental intentions by tapping into a stronger parental care motivation [32
]. Indeed, the results from four separate studies consistently supported this hypothesis, at least, regarding environmental behavioral intentions. These results are aligned with previous research indicating that people behave in an environmentally more sustainable way for inclusive fitness reasons—without them necessarily always being consciously aware of this deeper motivation [21
]. Also, our meta-analytic exploration of the effect of parenthood status across the four studies helped to triangulate these findings.
Findings from environmental psychology and environmental demographics about the effect of having children on environmentalism have been somewhat inconclusive [22
]. One possible explanation for this is that these lines of research have generally focused on the proximate causes of environmental behavior (i.e., parents trying to meet children’s school-derived expectations regarding sustainable behavior at home; [62
]). In our studies, we focused on a deeper evolutionary motivation: people might behave in sustainable ways to make sure their children—thus, their genetic future—will have a clean environment to live in [3
Study 1 showed that a children-cue compared with a control condition indirectly increases environmental intentions through activating greater parental care. Study 2 replicated this finding. However, contrary to our prediction, own-children cues did not affect environmental intentions differently than a generic future generations cue. One potential explanation for this could be that there is some overlap between the cues as future generations also include your own biological offspring. This could be explained in terms of how humans’ semantic networks operate. The network, a multilevel and multi-node structure, can be activated by external stimuli. However, a stimulus usually activates not just one node or one level but elicits cross-activation [63
]. Nodes representing concepts (e.g., one’s children and future generations) are connected, and the stronger the connection, the faster and more effective the activation of one concept by another [64
]. Thus, thinking about future generations might activate concerns about one’s (future) children and the other way around, because the concepts could be semantically related. A second potential explanation refers to the accuracy of the motivational system. It could be that the motivational system is not perfect in detecting the difference between a cue of one’s own offspring and a cue of future generations.
Given that children act as connections with an abstract future [65
], an alternative explanation of our overall findings could be that an appeal to the welfare of one’s children, instead of activating parental care, reduces people’s temporal discount rates. In order to evaluate this possible explanation, Study 3 was carried out. In particular, Study 3 tested whether an increased parental care motive (instead of a reduced discounting rate) was indeed the mechanism that drove the effects seen in Studies 1 and 2.
The findings of Study 3 were consistent with kin selection theory, at least in terms of predicting greater environmental behavioral intentions. The children cue positively affected environmental behavioral intentions by increasing one’s parental care motivation. More importantly, the cue of having children did not reduce participants’ discount rates nor did it show any indirect effect on environmental behavioral and altruistic intentions through reduced discounting. Thus, it seems likely that each positive indirect effect of the children-based appeal over the environmental behavioral intentions was being driven by parental care. In addition, Study 3 also replicated previous research on time delays in environmental information, indicating that phrasing environmental consequences as being sooner (rather than delayed in time) strengthens people’s environmental intentions [47
]. Indeed, this result is consistent with the psychological distance literature indicating that the closer people perceive environmental threats, the more they tend to engage in mitigating actions [67
The results of Studies 1–4 consistently showed a positive indirect effect of children-cues (and manipulated parental care in Study 4) on environmental behavioral intentions through increased parental care motivation. But what about the direct effect of offspring cues on environmental outcomes? Although previous findings on this matter have been rather mixed (e.g., [26
]), in Study 4, we tested the effect of a children-cue and parental care independently. Our results did not provide support for a unique direct effect of the children-cue on environmental behavioral intentions nor on environmental altruistic intentions. The lack of children-cue/kin-care manipulation priming effects could be explained in terms of weak effects of priming on intentions and behavior overall (for a review see Reference [68
]; e.g., [69
]) and the weak impact of automatic system activated by a prime on intentions and behavior; if some conditions are not met, for example, cognitive resources are not tapped [72
] or the priming is not sufficiently contextualized to activate certain reactions [74
]. Thus, only if the children-cue priming was sufficiently increasing parental care, then could we observe a slight change in environmental intentions, indicating the indirect effect. In other words, increased parental care created adequate conditions for reactions guided by the priming [75
]. Alternatively, the indirect-only effects [35
] seen in our studies might be due to the presence of a competing mediator that has yet to be unveiled. Such a competing mechanism should be positively influenced by child-cues but negatively related pro-environmental intentions thus canceling out a potential direct effect of child-cues on the dependent variables (e.g., inconsistent mediation [76
]). Although there might be multiple constructs that match these relationship patterns, as previously suggested by some authors [26
], two likely candidates are financial concerns and time constraints. Raising a newborn is usually associated with more expenses and less free time in a household. Then, as resources and time are being diverted into the new family member, relatively expensive and time-consuming pro-environmental lifestyles are not likely to be adopted. Future work should explore these ideas further.
Despite the lack of direct effects, however, Study 4 allowed us to explore whether the sustainability benefits of parental care are confined to manipulations in which this motive is activated within an environmental context (i.e., embedded in environmental messages). The results do not seem to suggest this. Instead, the results replicated the positive indirect effect of parental care on environmental behavioral intentions we observed in the previous studies. This result seems worth noting, as it suggests that policymakers could activate parental care in a variety of ways (and indirectly foster pro-environmental behavior) and not only by environmental messaging. Such versatility could probably enable the use of parental care motivation for sustainability purposes in a wider range of public policy campaigns.
Regarding the environmental altruistic intentions, findings across the four studies were less consistent. In particular, even though Study 1 showed the expected positive indirect effect of children-based appeals on environmental altruistic intentions, Studies 2–4 did not yield a similar effect. It could be that environmental altruistic intentions (e.g., donating, volunteering) are not perceived as directly affecting one’s children’s local environment and, thus, cannot be guided directly or indirectly by priming with children-cues. Instead, visible altruistic intentions might be more influenced by reputational concerns instead of parental care motivation. Developing a good reputation by means of altruistic displays tend to increase individuals’ overall fitness through indirect reciprocity [77
]. Indeed, in resource dilemmas, people tend to contribute more to the common pool when they believe that such contribution will improve their reputation [78
7.1. Limitations and Future Directions
Our research is not exempt from limitations. First, the present studies only focused on the indirect effects of children-cues on environmental behavioral and altruistic intentions. We did not explore whether cues of other genetically related relatives (e.g., siblings, grandchildren) also increase environmental intentions as kin selection theory holds. Future studies should build upon our results, investigating, for instance, whether grandchildren’s cues would produce the same results. Second, although our studies contained outcome measures that allow the exploration of a wide range of environmental intentions, many of them—but certainly not all—were fairly low-cost activities, making conclusions about the effects of children cues on high-cost intentions difficult to make. Similarly, participants were not requested to engage in actual environmental behavior, having to report their intentions only. Future research could fill this gap by testing the effect of the parental care motive on environmental activities that require bigger personal sacrifices as well as on actual behavior. Finally, our children cue did not indirectly lead to more pro-environmental intentions when compared to the generic future-generations cue in Study 2. We proposed that the overlap between the two cues could be the reason for the lack of difference, and future studies could test that hypothesis. For instance, a lexical decision task (LDT) could be applied [79
]. In such a task, reaction times towards presented categories are used to identify differences/similarities in semantic network activation [64
]. If a future generation cue activates the same nodes as offspring cue reaction times in an LDT should be similar. Thus, in order to study that further, a distinction between genetically similar future-generations and genetically non-similar future-generations categories could be tested.
Going back to the question raised at the beginning of this paper: are governments and the people who vote for them persuaded by appeals about the welfare of their children and grandchildren? Our results indicated that they are, though through an indirect evolutionary-rooted motivation: parental care. In particular, in the current research, we tested whether the care for children, an evolutionary relevant motive derived from kin selection, would be associated with people’s environmental intentions. Overall, the findings indicate that activating the parental care motive indirectly increases people’s environmental intentions. Our findings may have some practical implications. Environmental policymakers could convey environmental messages that accentuate the genetic interests of citizens more strongly (e.g., an appeal to Mother Nature; [10
]) but also messages stressing genetic interests that do not mention sustainability references (as seen in Study 4). Importantly, this does not imply that policymakers should encourage individuals to become parents sooner or have more children, considering the relatively large negative environmental consequences associated with larger populations [80
]. Instead of focusing on the fate of our planet, environmental policymakers could create child-based messages which will indirectly lead people to reflect on the negative consequences of environmental (in)actions and engage in more pro-environmental behaviors.