Monday, December 2, 2019

Nulliparous women remember survival scenarios involving a son better than those of non-related children; the authors find here evidence that memory has been sculpted by evolutionary processes

“Survival Processing of the Selfish Gene?”: Adaptive Memory and Inclusive Fitness. Patrick Bonin, Margaux Gelin, Betty Laroche, Alain Méot. Evolutionary Psychological Science, December 2 2019.

Abstract: The survival processing advantage in memory is the finding that items encoded in survival scenarios are remembered better than words encoded in survival-irrelevant scenarios or in deep encoding situations (e.g., pleasantness). Whether this mnemonic advantage, which is generally found in scenarios involving personal survival, can also be observed in scenarios involving the survival of other people, and in particular, genetically related others, has received little attention. In the present study, we asked nulliparous women to imagine being stranded in the grasslands of a foreign land without any basic survival items and to consider either their personal survival, the survival of their biological child, or the survival of an orphan. Compared to a pleasantness (control) condition, a survival processing advantage was found for the child survival group, which did not differ reliably from personal survival. Both the child and the personal survival conditions yielded better recall than the orphan condition, which did not reliably differ from the pleasantness condition. These findings provide further evidence for the view that memory has been sculpted by evolutionary processes such as inclusive fitness.

Keywords: Adaptive memory Survival processing advantage Inclusive fitness


Anecdotal evidence suggests that we do not provide the samelevel of help to strangers as we do to our relatives. It is hard to imagine a world in which parents faced with a life-or-death situation, such as a shipwreck in which the number of life boats is limited, would hesitate to save the life of their own biological child rather than that of an unrelated child. To our knowledge, such a world does not exist: We do not behave altruistically in an undifferentiated manner (Buss2019). Helping has been found to vary as a function of genetic relatedness (Burnstein et al.1 994; Fitzgerald and Whitaker 2009; Stewart-Williams 2007,2008). That being said, human beings belong to a highly cooperative species since we have lived in small and interdependent groups for most of our evolution (Hrdy2009). Social species exhibit an impressive array of altruistic behaviors, some of which are directed to unrelated others (e.g., reciprocal altruism, Trivers1971), and such altruistic behaviors have perhaps evolved to solve issues related to group living (Marsh2016).

Turning to the adaptive memory literature, the survivalprocessing advantage initially discovered by Nairne et al.(2007) is now a well-established finding. However, the ques-tion of whether this memory advantage extends to the survivalof other people (Kostic et al.2012; Krause et al. 2019; Seitz et al. 2018; Weinstein et al. 2008) or is restricted to personal survival (Cunningham et al.2013; LedingandToglia2018) is a matter of debate because of discrepant findings in the literature. In the present study, we put forward the hypothesis thata survival processing advantage should be observed with an imaginary scenario involving the survival of a biological child because, from an evolutionary perspective, offspring are vehi-cles for their parents’ genes (Buss2019). More importantly,we also hypothesized that, in line with the inclusive fitness and kin-selection theories (Hamilton1964), the survival effectin memory, if any, should be smaller when the recipient of helping behaviors is a non-biological child, namely an orphan.The findings were clear-cut. First of all, we were able to replicate the original survival processing advantage (Nairne et al.2007): Encoding words in relation to a personal survival situation yielded better memory performance than rating words for their pleasantness. It should be remembered that pleasantness has often been used as a control condition to evaluate survival processing because it is a deep processing task (e.g., Kazanas and Altarriba 2017; Nairne and Pandeirada 2010;O lds et al. 2014). When survival was directed to a biological child, a survival processing advantage was also found. In linewith Seitz et al.’s (2018) parenting scenario involving the survival of the participants’babies in the grasslands, we found a reproductive advantage in memory that did not differ reli-ably from a personal survival advantage. More importantly, in accordance with the inclusive fitness theory (Hamilton1964)and kin selection theory (Smith1964), the level of recall var-ied as a function of genetic relatedness: More words wererecalled in a survival situation involving a biological childthan in a survival situation involving an orphan, and the latter condition did not differ reliably from the pleasantness condition.

From this pattern of findings, a critical question arises.Why did Krause et al. (2019) fail to find a differential survival processing advantage in their experiments comparing different types of kin vs. non-kin conditions? In Krause et al.’s research, different survival conditions were compared: personal survival, survival of family members,a youngest blood relative, unrelated people. It should be remembered that the authors found that compared to thepleasantness control group, the recall rates were similar across the “kin,” “friend,” and “famous” groups. Thus,the pattern of recall did not show that the survival of kin produced a memory advantage compared to that of non-kin. It remains possible that the social relationships that Krause et al. took into account were not specific enough for differential effects on memory performance to emerge. Finally, it cannot be excluded that our scenarios and Krause et al.’s scenarios are too different to be compared directly. In effect, Krause et al. modified the original survival scenario only slightly, and the different scenarios were similar, whereas in the current study, more modifications were made to the original survival scenario. The strength of our study is that we took care to be specific by comparing children who are biologically relatedto their mothers with children who are not biologically related (we did not therefore include a generic“unrelated other”condition such as“strangers”). Moreover, we decided to include only female participants because it hasbeen found that, in general, women are more interested in children than men are (Cárdenas et al.2013; Charles et al.2013; Maestripieri and Pelka2002), and they also take more time to care for them (Babchuk et al.1985; Buss 2007).

Some readers might be concerned about the finding that nosurvival processing advantage occurred with an orphan. Does this finding mean that people do not behave “altruistically” towards orphans? Certainly not. First of all, our findings concern memory performance and tell us nothing about the emotional responses people may have towards orphans. As suggested by Marsh (2016): “Parental care is such an ordinary phenomenon that we often fail to think of it as altruism. But itclearly meets the definition, which is a behavior that improvesthe welfare of another individual at the expense of the altruist.”(p. 62). Parental care is often provided to distantly relatedchildren or to unrelated children (Hrdy2009), including chil-dren who are adopted. According to Marsh (2016), care-based altruism results from the co-option of systems that initially evolved to support parental care. Here, we have shown that there are differences at a cognitive level in the way things are remembered when they have been processed in a survival situation involving a biological child compared to a biologically unrelated child. Second, if we take a closer look at the memory performance, we observe that the words processed in a survival situation in the orphan condition were recalled well because they were recalled at the same level as the words that were encoded deeply, that is for their pleasantness. One important aspect worth noting is that the words in the orphan condition were not recalled less well than the words in the pleasantness condition—a deep encoding condition. Thus,there is still some level of altruistic behavior at a cognitive level that is deployed in the case of orphans.

Our findings have strong theoretical implications since they show for the first time that the survival processingadvantage has to do with inclusive fitness and kin selection (Hamilton1964;Smith1964). From a general stand-point, they reinforce the evolutionary view of memory according to which our memory is still peculiarly attunedtoward processing issues that our ancestors faced during the distant past, such as finding food, drinking water, andprotection from predators both for themselves and also for their kin, and in particular for their children. It is already clear that more work will be needed to investigate further whether human memory is tuned to encode things better for different types of kin relationships such as sibling, parental, and grandparental relationships. We are aware of the fact that having only nulliparous women as participants constitutes a limitation of our study. Perhaps a different pattern of results would have been found if our participants had been mothers. Furthermore, it remains an avenue for future research to conduct the same studyon young men. It is possible to anticipate that different findings will emerge because men and women faced dif-ferent reproductive issues in the distant past. While women are 100% sure of their parenthood, ancestral men were(and indeed modern men still are) confronted with the problem of paternity uncertainty due to cryptic ovulation(Buss2019). This reproductive problem faced specifically by men would account for their lesser interest (e.g.,Cárdenas et al.2013; Charles et al.2013;  Maestripieri and Pelka2002) and investment in children compared to women (e.g., Babchuk et al.1985;Buss2007). Based on these findings, we anticipate that men will recall more words in both the personal survival scenario and childs cenario than in the pleasantness condition, but that even when the risk of not being the biological father is low,men will recall less words in the child condition than will nulliparous women. However, in a survival scenario inwhich men have to imagine that there is a high risk that the child they must take care of is not their biological child, our prediction is that the recall rate will be closeto that found here in the orphan condition. Finally, in th efuture, it would be interesting to test whether grandparents’memory for items in survival situations involving their grandchildren differs as a function of the certainty of genetic relatedness. Likewise, a maternal grandmother is more genetically certain of her grandchildren than a paternal grandfather and, as found by DeKay (1995,reported by Buss2019), maternal grandmothers are closerto and invest more resources in the grandchild than pater-nal grandfathers.

The question of the proximate mechanisms that underpin the survival processing advantage in memory is an issue which has given rise to a large number of studies. Different proximate mechanisms have been put forward and, according to Krause (2015), at least eight candidate mechanisms couldcontribute to the survival memory advantage. Although it was not the aim of our study to address this issue, our findings nevertheless suggest that self-reference, even though it certainly plays a role in this memory effect (Cunningham et al.2013), is not the sole proximate mechanism involved. Indeed,if this were the case, survival-processing effects should have been restricted to the personal survival condition, unless bio-logical children are considered to be part of the parents’self. In line with the latter claim, the literature on the self-reference effect reports that the mnemonic difference between self-reference and other-reference conditions is attenuated or eliminated when the other-reference conditions correspond to aparent or to a best-friend (Bower and Gilligan1979; Symons and Johnson1997).

Elaboration is a basic memory mechanism which certainlyplays a role in the survival processing effect as suggested bycertain studies (e.g., Bell et al.2015;Röeretal.2013; Wilson2016). Nairne et al. (2017a,b) initially reported that survival processing increases not only true memories but also false memories. Here also, we found a higher number of extra-list intrusions in the personal survival scenario than in the pleasantness condition. This type of finding—namely an increase in both true and false memories—was later extended by Howe and Derbish (2010,2014) and Otgaar and Smeets (2010),while other studies have failed to find significant effects ofs urvival processing on extra-list intrusions (Bonin et al.2019b; Gelin et al.2017). According to Howe and Derbish (2014), because elaboration is known to increase both true and false memories, the effect of survival processing sometimes found on both true and false memories may be due to the need for greater levels of elaboration in order to rate words for their survival values. Interestingly, in the current study, we found that the greatest number of extra-list intrusions occurred in theorphan condition. Overall, the current pattern of findings accords with the idea that elaboration underpins (at least inpart) the survival processing advantage.5

As found in some previous studies (e.g., Seitz et al.2018),mean relevance ratings were higher in the pleasantness condi-tion than in any of the other conditions. However, and morespecifically, recall performance was higher for both the per-sonal and the child survival scenario than for the pleasantnesscontrol condition. It is also interesting to note that the ratingsin the child condition were significantly higher than in thepersonal survival, but this difference did not translate into arecall difference between these two conditions. The pattern offindings for relevance ratings and recall rates suggests that theoverall difference in recall rates across conditions was not aresult of differences in depth of processing or in congruity,since it is generally accepted that words that are processed ata deeper level (Craik and Tulving1975) or that are morecongruent in a given encoding context (Butler et al.2009;Craik2002) are often recalled more accurately than words thatare processed more superficially or that are rated as being lesscongruent (Seitz et al.2018).

There are studies which suggest a relationship between empathy and altruistic behaviors (Marsh2016). However,the analyses performed with the scores obtained from the Basic Empathy Scale (Carré et al.2013) did not reveal thatthis dispositional trait played a role in the memory performance observed in the different encoding conditions that we considered. Emotional closeness has been found to be a prox-imal cause of altruism that partially mediates the impact of genetic relatedness on the willingness to act altruistically(Korchmaros and Kenny2001). In the current study, we didnot assess our participants’willingness to help as a function ofdifferent types of social relationship in an ancestral survivalsituation. However, because we were interested in knowingwhether willingness to help an orphan versus a biological child would mirror memory performance as indexed by recallrates, as described in more detail in the Supplementary Material, we designed a questionnaire using LimeSurvey( and this was completed online by apool of 84 undergraduates (only nulliparous women weretaken into account). We collected ratings using Likert scalesof willingness to help in a survival situation—by providingfood, drinking water, and protection for both an orphan and abiological child who were said to be weak. In addition, wecollected ratings for other types of kin (e.g., mother, sister,cousin) and non-kin (friend, neighbor, stranger) relationships.The findings (see the Results section in the Supplementary Material) turned out to be in line with those reported in theliterature on altruistic behaviors (e.g., Burnstein et al.1994;Fitzgerald and Whitaker2009; Stewart-Williams2007,2008),that is to say, in a hypothetical survival scenario, women were more willing to aid close kin (e.g., child, mother) than distant kin (e.g., cousin), more willing to help distant kin than neighbors,“acquaintances,”or“strangers”(see Figure1A in the Supplementary Material). Interestingly, the level of help for “friend” was comparable to that of“cousin”(Figure1A).More importantly, as far as the comparison between biologicalchild and orphan is concerned, women chose to help theirbiological child more than an orphan. However, the level of help for“orphan”was close to that for“cousin”(Figure1A).To conclude, Krause et al. (2019) made the strong claim that kin selection is one more fitness-relevant scenario that hasbeen found to be either unrelated or irrelevant to the survival processing advantage. The findings from the present study suggest just the contrary, namely that the survival processing advantage varies as a function of genetic relatedness, at least when the kin in question are biological children who, from an evolutionary point of view, ensure the perpetuation of our genes. Thus, our findings are in agreement with the claim put forward by Nairne et al. (2007) that “mnemonic processes likely operate more efficiently when dealing with fitness-relevant problems."

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