Sadness pervades affective responses to death; words chosen to represent perceptions of others’ feelings towards death suggest that we perceived others as feeling more negative about death than they we do ourselves

Miller-Lewis LR, Lewis TW, Tieman J, Rawlings D, Parker D, Sanderson CR (2021) Words describing feelings about death: A comparison of sentiment for self and others and changes over time. PLoS ONE 16(1): e0242848, Jan 6 2021. https://doi.org/10.1371/journal.pone.0242848

Rolf Degen's take: https://twitter.com/DegenRolf/status/1347045740305133572

Abstract: Understanding public attitudes towards death is needed to inform health policies to foster community death awareness and preparedness. Linguistic sentiment analysis of how people describe their feelings about death can add to knowledge gained from traditional self-reports. This study provided the first description of emotive attitudes expressed towards death utilising textual sentiment analysis for the dimensions of valence, arousal and dominance. A linguistic lexicon of sentiment norms was applied to activities conducted in an online course for the general-public designed to generate discussion about death. We analysed the sentiment of words people chose to describe feelings about death, for themselves, for perceptions of the feelings of ‘others’, and for longitudinal changes over the time-period of exposure to a course about death (n = 1491). The results demonstrated that sadness pervades affective responses to death, and that inevitability, peace, and fear were also frequent reactions. However, words chosen to represent perceptions of others’ feelings towards death suggested that participants perceived others as feeling more negative about death than they do themselves. Analysis of valence, arousal and dominance dimensions of sentiment pre-to-post course participation demonstrated that participants chose significantly happier (more positive) valence words, less arousing (calmer) words, and more dominant (in-control) words to express their feelings about death by the course end. This suggests that the course may have been helpful in participants becoming more emotionally accepting in their feelings and attitude towards death. Furthermore, the change over time appeared greater for younger participants, who showed more increase in the dominance (power/control) and pleasantness (valence) in words chosen at course completion. Sentiment analysis of words to describe death usefully extended our understanding of community death attitudes and emotions. Future application of sentiment analysis to other related areas of health policy interest such as attitudes towards Advance Care Planning and palliative care may prove fruitful.

Discussion

Summary of findings

Understanding public attitudes and feelings towards death is needed in order to inform health policies [3]. This study provided the first description of emotive attitudes of people asked to consider death utilising sentiment analysis. Applying multidisciplinary methodologies to a novel activity gave a deeper understanding of affective death attitudes in a community sample. We analysed the emotional sentiment of words people chose to describe feelings about death, for themselves, for perceptions of others, and for changes over the time-period during exposure to a course about death. The results demonstrated that text-sentiment analyses can provide a meaningful approach to death attitude research, consistent with previous linguistic investigations [20–22, 29]. ‘Sad’ was a word that was prevalent throughout, regardless of whether referring to feelings for oneself or for others, or feelings captured at the beginning or ending of a course about death and dying. Thus ‘sad’ feelings were universally linked to death. Nonetheless, the MOOC participants commonly chose words to express their perception of other’s feelings towards death that were considerably more emotionally negative (‘fear’, ‘scary’, ‘loss’) than the words chosen to express their own feelings towards death (‘inevitable’, ‘peace’, ‘natural’). When we moved beyond the self-report of words themselves and applied numeric sentiment scores to the words chosen, we found that the sentiment expressed to represent one’s own perspective was significantly more positive compared to those representing the perceived perspective of others. The words chosen to represent the feelings of others indicated sentiment that was more unhappy/unpleasant, more arousing/excitable, and more submissive/dominated by external forces. This aligns with findings from other studies [5, 59, 60]. Our findings leave us with the question of why the MOOC participants think that others feel so differently about death than they do themselves? Part of the explanation is likely to lay in the self-selected nature of our sample of people who chose to participate in a course about death, a considerable proportion of whom identified as health professionals and may have seen themselves as more informed and conditioned to death. But, the sentiment of the words chosen to represent the perceived feelings of others does demonstrate the assumptions people make about other peoples’ negative reactions regarding death. It is possible that these assumptions have implications for the willingness of people to start conversations about death and dying with the people around them. If we perceive that others will become distressed by bringing up the topic of death, are we less likely to attempt raising the topic? Does this avoidance then leave important things unsaid?

When we compared the types of words participants chose to describe their personal feelings about death at the beginning and the end of the MOOC, we found that the most frequently mentioned words were quite similar at both time points (e.g., inevitable, peaceful, peace, natural, sad), but that mentions of more negative words like ‘sad’ reduced considerably in frequency over time, along with a corresponding increase in mentions of words related to acceptance and comfort. The specific words chosen by individuals at each time point showed more changes over time than stability. When the sentiment of the words chosen to express personal feelings about death at both time-points was analysed, we found that participants chose happier valence words, less arousing words, and more dominant words at the end of the course about death than they did at the beginning. This finding suggests that participating in an online course about death and dying may have had a positive effect on the type of language people chose to express their feelings about death, with the emotional sentiment of the language used by the end of the course subsequently becoming more pleasant/positive, calmer, and more internally controlled. Given that the sentiment of words deals with emotion in relation to an issue, this suggests that over time the course may has assisted participants in becoming more emotionally accepting in their feelings and attitude towards death. It is also important to note therefore that spending time thinking and learning about death over a five-week period did not appear to have a negative emotional impact on course participants. This finding is consistent with our findings from research with our 2016 cohort using formal scale measures [6] and evaluation questionnaires [5] geared more towards behavioural indicators. The findings of the present study indicate that participation in the MOOC potentially had a positive emotional influence on the participants, in addition to the behavioural and cognitive influence demonstrated in earlier studies [5, 6]. This offers valuable triangulating evidence validating the potentially beneficial effects of participating in an online course about death.

Our multivariate findings demonstrated that the positive changes in sentiment occurred similarly for participants regardless of education, occupation, and location. However, an interesting influence of age was found on the rate of change in valence and dominance sentiment scores from the beginning to the end of the course. From the outset, younger participants scored lower on death sentiment valence and dominance, and compared to older participants, younger participants experienced greater change during course participation on the sentiment of the language chosen to express personal feelings about death, with greater increases in the pleasantness (valence) and dominance (power and control) in the words they chose at the end of the course. This may be in part due to younger participants having lower valence and dominance scores at baseline, meaning there was more opportunity for improvement in their scores by the end of the course. For older participants, the influence of a course discussing death is perhaps less due to having more personal exposure and proximity to death in their life and thus greater mortality salience. Therefore, it’s possible that participation in an online course about death may be especially beneficial for younger people, potentially assisting them to become less emotionally negative and more accepting of death and its inevitability.

Implications

The results from this study provide further validation of the emotive nature of death and dying. It provided quantification of the strength and direction of affective responses to death and the differential perceptions of death attitudes participants applied to others in the community. Word sentiment analysis was a useful adjunct to traditional self-reports, and is arguably less invasive.

The words and labels used in clinical encounters can have differing effects upon patients and clinicians. For example, Tayler and Ogden [81] reported the tendency of doctors to use euphemisms instead of the direct term ‘heart failure’ due to the dilemma of the latter causing more negative emotional reactions in patients. On the other hand, a study of more benign conditions (gastroenteritis/tonsillitis) found the use of clinical language over lay language can validate the patient’s sick role and can increase confidence in the doctor [82]. The use of euphemisms to avoid the word death is reportedly common, and accompanied by the potential for misunderstandings [20, 22, 58]. Thus, words are not neutral. They can have an impact on patients and people–they can bring people with us or alienate them, they can be interpreted differently by people, they can be delivered in personal or impersonal ways, and they can sway a person’s actions. There may be implications worth exploring for clinical settings, particularly for awareness of the choice of words verbalised in clinical encounters related to the end-of-life. Understanding the sentiment of words provides valuable insight into the emotional connotations tied to words we use, and could be useful for guiding clinical conversations in palliative care [20, 22].

The knowledge gained from this study about community death attitudes could potentially inform the creation of dialogue and messaging used in public health campaigns about the end-of-life preparedness. The use of higher valence and dominance words might bolster the persuasiveness of campaigns in a way that potentially leads to more effective emotional engagement and behavioural activation in target populations [37, 83].

Strengths, limitations, and future directions

Whilst this study was based on a large sample, several potential limitations require consideration. Like most MOOC samples, our sample is unlikely to be representative of the general population [62–64]. Participants were a self-selected sample of people in the community who chose to enrol in a course about death, and therefore may have been more likely to feel comfortable with the topic of death from the outset than people in the general population. Our sample also included a considerable proportion of people who identified as health professionals, which may impact on death attitudes given their greater opportunity for exposure and possibility of more desensitised death-related emotions. The sample was also comprised of a vast majority of females, which meant that gender comparisons could not be meaningfully undertaken. Furthermore, the results of the present study may be somewhat less representative of younger people and those residing outside Australia, because enrolees who subsequently went on to participate in the MOOC activities were slightly older and more likely to be located in Australia than those who enrolled but did not participate. Replication of the study with a representative community sample would be a valuable avenue for future research, to garner a stronger understanding of socio-demographic variations in the sentiment of words about death. Comparing death word sentiment for various age cohorts in the community with differing death exposure experiences is particularly needed, as well as direct dyad comparisons of self-other death attitude perceptions. It would also be informative to examine how respondents’ death word sentiment relates to their self-reported fear of death and other emotive death attitudes rated on standardised instruments. This could enable a broader insight into various aspects people associate with death [7].

A strength of this study was the inclusion of a longitudinal component that observed changes over time in the sentiment of words chosen to express feelings about death. However, course attrition meant that slightly less than half of participants that provided words at baseline also provided data at the end of the course. It is possible that those participants who were less inclined to complete the Time 2 activity were also less likely to have experienced a positive emotional response to the course. Nonetheless sensitivity analyses using alternative approaches (Multiple Imputation) to account for the missing data obtained similar results and conclusions to those using the complete-case sample. In the final week of the course when participants were asked to provide three death words again, it was possible for them to go back and look at their previous word choices from the beginning of the course. It is not clear how many participants went back and checked their first response, versus those who followed instructions to simply go with their instinctual response. It is not known what effect any comparative check by participants may have had on the words they chose to report at Time 2.

Of further importance is that our longitudinal assessment of change over time did not include a comparison group of people who were not exposed to the MOOC. Without this comparison group, it is impossible to rule out alternative explanations for the reasons word sentiment scores changed from the start to the end of the course. Other factors occurring within lives of participants while completing the MOOC may have caused changes on death sentiment over time that were not related to MOOC completion. Future research including a control group is warranted.

In this study, we applied sentiment analysis to three specifically chosen content words rather than to a written sentence, or a more generalised analysis of written text. However, it is possible that by giving participants explicit instructions we obtained more expressive emotional content words than we would have if a sentence was requested, given that typically only a small proportion of words used are classified as emotive [14]. The results may have differed if the activity used a sentence instead, but it may have reduced the emotive data elements provided, being more likely to have been limited to one core theme/lemma. Alternatively, utilising a much larger textual response may have provided a deeper understanding of emotions, as there is evidence that non-content function words such as prepositions and pronouns can also convey affective content [84, 85]. It would be worthwhile to explore the use of these different methodologies in future research, such as examining the effect of the online course over time by comparing the sentiment expressed in larger bodies of general comments/posts made at the beginning and at the end of the course.

Another potential limitation is that Warriner and colleagues’ [37] lemma database is based on rating words on an ordinal 1-to-9 scale, rather than a continuous interval scale. There may not be a uniform difference reflected between a rating of 1-to-2 as there is for 8-to-9. Very recently, new slide-rating methods for valence scores have been tested, which may provide a fruitful direction for future studies to utilise, if norms are developed [86].

The current study focussed on words used to describe feelings about death and dying, and has provided valuable insights into the way people feel about this issue. There is considerable potential for applying sentiment analysis to other related constructs, such as words chosen to describe feelings about Palliative Care, Advance Care Planning and Voluntary Assisted Dying. Such future research may help us better understand the nuances in community attitudes towards these important social policy issues. The possibilities of sentiment analysis as a methodology to detect emotional states of respondents also deserves future research attention. Previous studies have successfully used sentiment analysis to detect mental health conditions and level of threat in social media statements [17, 32]. Future research could pursue word sentiment as a method to detect emotional distress in health settings (e.g., carer bereavement risk), which could activate early intervention efforts.

Born to Shop? Past research indicating that deal-prone consumers are likely to have one or more deal-prone parents has suggested that there may be genetic factors involved in the appeal of retail sales promotions

Born to Shop? A Genetic Component of Deal Proneness. Robert M. Schindler, Vishal Lala, and Jeanette E. Taylor. Journal of the Association for Consumer Research, Jan 5 2021. https://www.journals.uchicago.edu/doi/abs/10.1086/710244

Rolf Degen's take: https://twitter.com/DegenRolf/status/1346844597289410561

Abstract: Past research indicating that deal-prone consumers are likely to have one or more deal-prone parents has suggested that there may be genetic factors involved in the appeal of retail sales promotions. We report the results of a study of monozygotic and dizygotic same-gender twins that indicate a role of hereditary factors in the degree of consumer interest for at least some types of promotional deals.

Maybe rodents regulate a ratio of protein to dietary carbohydrates in order to achieve metabolic benefits (reduced insulin levels, improved blood glucose control, and, in the long term, reduced weight & fat gain)

What does self‐selection of dietary proteins in rats tell us about protein requirements and body weight control? Patrick C. Even  Joséphine Gehring  Daniel Tomé. Obesity Reviews, January 5 2021. https://doi.org/10.1111/obr.13194

Rolf Degen's take: https://twitter.com/DegenRolf/status/1346836414521081859

Summary: Omnivores are able to correctly select adequate amounts of macronutrients from natural foods as well as purified macronutrients. In the rat model, the selected protein levels are often well above the requirements estimated from the nitrogen balance. These high intake levels were initially interpreted as reflecting poor control of protein intake, but the selected levels were later found to be precisely controlled for changes in dietary protein quality and adjusted for cold, exercise, pregnancy, lactation, age, etc. and therefore met physiological requirements. Several authors have also suggested that instead of a given level of protein intake, rodents regulate a ratio of protein to dietary carbohydrates in order to achieve metabolic benefits such as reduced insulin levels, improved blood glucose control, and, in the long term, reduced weight and fat gain. The objective of this review was to analyze the most significant results of studies carried out on rats and mice since the beginning of the 20th century, to consider what these results can bring us to interpret the current causes of the obesity pandemic and to anticipate the possible consequences of policies aimed at reducing the contribution of animal proteins in the human diet.

Chimpanzees: Adolescent males mated with nulliparous females and reproduced primarily with these first-time mothers, who are not preferred as mating partners by older males

The development of affiliative and coercive reproductive tactics in male chimpanzees. Rachna B. Reddy, Kevin E. Langergraber, Aaron A. Sandel, Linda Vigilant and John C. Mitani. Proceedings of the Royal Society B: Biological Sciences, January 6 2021. https://doi.org/10.1098/rspb.2020.2679

Rolf Degen's take: https://twitter.com/DegenRolf/status/1346820516317949954

Abstract: Like many animals, adult male chimpanzees often compete for a limited number of mates. They fight other males as they strive for status that confers reproductive benefits and use aggression to coerce females to mate with them. Nevertheless, small-bodied, socially immature adolescent male chimpanzees, who cannot compete with older males for status nor intimidate females, father offspring. We investigated how they do so through a study of adolescent and young adult males at Ngogo in Kibale National Park, Uganda. Adolescent males mated with nulliparous females and reproduced primarily with these first-time mothers, who are not preferred as mating partners by older males. Two other factors, affiliation and aggression, also influenced mating success. Specifically, the strength of affiliative bonds that males formed with females and the amount of aggression males directed toward females predicted male mating success. The effect of male aggression toward females on mating success increased as males aged, especially when they directed it toward females with whom they shared affiliative bonds. These results mirror sexual coercion in humans, which occurs most often between males and females involved in close, affiliative relationships.

4. Discussion

The results presented here suggest that adolescent male chimpanzees, who cannot effectively compete with older males nor sexually coerce adult females, employ at least two behavioural tactics to mate and reproduce. First, as reported in previous research, adolescent males appear to target adolescent, nulliparous females as mating partners; they mate with nulliparous females frequently and father their first offspring more often in adolescence than they do in adulthood [42,48]. Our findings also corroborate past research indicating that nulliparous female chimpanzees are less preferred as mating partners than are parous females. Specifically, as male chimpanzees transition from adolescence to adulthood and rise in dominance rank, they show less sexual interest in nulliparous females and target them for aggression infrequently [47]. High-ranking males also rarely father the first offspring of these females [33–37,42]. Second, mating success for adolescent and young adult males was predicted by the strength of affiliative bonds that males formed with females. Male aggression, by contrast, had a relatively weak relationship with mating success, but one that strengthened as males grew older and increasingly dominant to females.

These findings increase our understanding of the nature of sexual coercion in chimpanzees. We have recently shown that adolescent and young adult males selectively direct aggression toward females with whom they form strong affiliative bonds [49]. Here, we demonstrate that aggression has a reduced effect on mating success outside of these bonds for young, adolescent males who are not yet physically mature and unlikely to dominate females [49,54,71]. Instead, mating success increases when an older adolescent or young adult male directs aggression to a female with whom he frequently affiliates and can dominate.

These results complement prior research that indicates aggression, mating and reproduction are linked in chimpanzees [28,30,31] and clarify the role that affiliation plays in creating those linkages. Specifically, sexual coercion is more effective when adolescent and young adult males have affiliative bonds with the females they attack. One reason may be that females suffer higher costs if they refuse to mate with males with whom they frequently affiliate compared to males with whom they rarely affiliate [12]. The nature of these costs remains to be explored. Nor is it clear whether and how affiliative relationships with males benefit female chimpanzees. It is important to note that our findings are consistent with patterns of intersexual aggression in other species where males are highly aggressive to females with whom they share bonds. This includes hamadryas baboons (Papio hamadryas), where females live in one-male groups, and most social activity is directed by the single males in these groups, i.e. ‘leader males’. After being attacked by their leader male, hamadryas females appear fearful and follow him even more closely than they had previously [72]. In our own species too, many women are subject to frequent sexual coercion by their male partners, but often remain in such relationships for reasons that vary widely [73].

Scant data exist about the proximate psychological mechanisms that underlie male aggression and female compliance in chimpanzees. However, investigating these proximate mechanisms may provide information about how bonds that affect paternity in chimpanzees might lead to a human-like social system [74]. One interpretation consistent with our preliminary observations is that male aggression toward their social partners is motivated by sexual possessiveness (e.g. [73]), and that females have a psychologically distinct experience when attacked by a male with whom they have an affiliative bond. For example, adolescent and young adult males make direct attacks on male peers infrequently, but when they do so, it is when another male mates or attempts to mate with one of their female social partners [49]. Anecdotally, when female chimpanzees received aggression from an adult male who did not have a strong affiliative bond with them, they often just screamed and ran away. Females receiving similar aggression from males with whom they shared strong affiliative relationships, however, react in an entirely different way. When attacked, these females remain in place, lunge toward their male partners while clutching their arms, rocking back and forth, and screaming repeatedly until making choking sounds.

Our study has several limitations. First, we cannot evaluate the relative impacts of affiliation and aggression on adolescent male paternity success. Only seven males in this study have reproduced thus far, siring 15 offspring, creating a small sample to make strong inferences. Our preliminary findings based on this small sample suggest that males who affiliate with and direct aggression to specific females gain a reproductive advantage with those females, but additional data are clearly needed. As these data accumulate, evaluating the effects of affiliation and aggression on male reproduction will be complicated because additional factors that we have not considered will require examination. For instance, we are likely to have underestimated the importance of sexual coercion, as it may act to ensure mating exclusivity as well as increasing a male's ability to mate with a specific female [12]. In this context, aggression is often used to initiate consortships in chimpanzees, where males lead females away from other community members and mate with them exclusively for several days (e.g. [21]). The challenge of maintaining exclusivity is not uniform. It may be relatively easy for high-ranking males because fewer males will challenge them to mate, or easier to accomplish with nulliparas, who are not preferred mating partners [47]. Second, we conducted this study over a relatively short period spanning two years, which covered only a single reproductive cycle for most females. Additional research is required to determine whether affiliative bonds between males and females endure and whether the patterns of aggressive and affiliative behaviour between bonded pairs persist and impact male reproduction over the long term (e.g. [30,37]). Determining whether such long-term relationships exist and how they impact male mating and reproductive success will improve our understanding of male chimpanzee development and the functional consequences of their behaviour.

Our findings also provide insights into the evolution of human pair bonds. Although the mechanisms that ensure paternity certainty in our species are diverse, including intimate partner violence [73–75] and larger cultural structures (e.g. religion: [76,77]), our finding that affiliative bonds between males and females appear entwined with sexual coercion in one of our two closest living relatives suggests that this aspect of intersexual relationships may be embedded deeply in our past.

Previous research suggests that choice causes an illusion of control—that it makes people feel more likely to achieve preferable outcomes, even when they are selecting among options that are functionally identical

Does Choice Cause an Illusion of Control? Joowon Klusowski, Deborah A. Small, Joseph P. Simmons. Psychological Science, January 5, 2021. https://doi.org/10.1177/0956797620958009

Abstract: Previous research suggests that choice causes an illusion of control—that it makes people feel more likely to achieve preferable outcomes, even when they are selecting among options that are functionally identical (e.g., lottery tickets with an identical chance of winning). This research has been widely accepted as evidence that choice can have significant welfare effects, even when it confers no actual control. In this article, we report the results of 17 experiments that examined whether choice truly causes an illusion of control (N = 10,825 online and laboratory participants). We found that choice rarely makes people feel more likely to achieve preferable outcomes—unless it makes the preferable outcomes actually more likely—and when it does, it is not because choice causes an illusion but because choice reflects some participants’ preexisting (illusory) beliefs that the functionally identical options are not identical. Overall, choice does not seem to cause an illusion of control.

Keywords: choice, illusion of control, open data, open materials, preregistered

General Discussion

Across 17 studies, we found no evidence that choice causes an illusion of control. Choice rarely made people feel more likely to achieve preferable outcomes when all options were functionally identical, whether we used different outcome measures (Studies 1–3), made the process visual (Study 4), varied the levels of uncertainty (Studies 5–7), or increased the subjectivity of the outcome evaluations (Studies 8 and 9). Choice had such effects only when it conferred actual control (Studies 10 and 11). In the rare cases in which choosers felt more likely to achieve preferable outcomes (Studies 12–15), choice seemed to reflect people’s preexisting beliefs rather than cause an illusion (Studies 16 and 17).

Our findings that a purported effect of choice results from an alternative account shares similarities with other reinvestigations of classic findings. Specifically, Chen and Risen (2010) showed that what looks like a choice-driven attitude change via cognitive-dissonance reduction in fact occurs because the choice is used to select people with different attitudes in the first place. Similarly, Tong, Feiler, and Ivantsova (2018) showed that what appears as choice-driven overoptimism via motivated reasoning emerges because choice reveals options that people already overestimate. Likewise, we revisited the highly influential and widely accepted phenomenon that choice causes an illusion of control. We found that such patterns rarely occur in cleanly designed experiments, and when they do, they are due to the choice reflecting people’s preexisting beliefs rather than causing an illusion. Together, this line of work suggests that some purported effects of choice may be due to the choice acting as a selection mechanism—among either different participants or different options—rather than as a cause of such effects.

Limitations

Despite our attempts to provide a comprehensive investigation, multiple questions remain.

First, our research does not address what might moderate the difference between the nonsignificant (Studies 1–11) and the significant (Studies 12–15) effects of choice. One possibility is that the probability estimates used in the latter studies are more sensitive than the other measures. In fact, our result from Study 15, which directly compared the probability estimates and multiple-choice measures, seems consistent with this conjecture. However, the nonsignificant coefficients in Studies 1 to 9 do not have a consistently positive sign, which is not what one would expect if the measures were merely less sensitive. Moreover, Studies 10 and 11 directly show that these measures were sensitive enough to respond when the choice made the preferable outcomes actually more likely. Another possibility is that evaluating multiple options in Studies 12 to 15 makes people more likely to develop normatively incorrect beliefs and hence more likely to show patterns that appear consistent with a choice-driven illusion of control. When one evaluates multiple options, there is a greater number of ways to express normatively incorrect beliefs (vs. only one way to express the normatively correct belief) than when one evaluates a single option, which might facilitate such beliefs. However, our results from Studies 12 to 14 indicate that the number of evaluated options does not always moderate the effect of choice. Although our research did not address these puzzling discrepancies, subsequent research could examine what may explain them.

Second, we do not know what led a subset of participants to demonstrate preexisting illusions, even when we explicitly informed them that all options have identical prospects (Studies 16 and 17). It is possible that certain individuals were prone to forming these beliefs because of past experiences, superstitious thinking, or distrust, but our research did not address what causes these beliefs or whether they are generalizable to people outside of our samples (Harris & Osman, 2012; Risen, 2016, Sharpe, Adair, & Roese, 1992). Future research could examine what individual or situational factors can lead people to develop such beliefs in the face of instructions that contradict them.

Third, our research focused on choice and thus did not address other factors that might truly cause an illusion of control. Previous research suggests additional factors that might cause an illusion of control (e.g., competition, familiarity, active involvement; Langer, 1975; Martinez et al., 2009). Although our research suggests that choice is unlikely to cause an illusion of control itself, it is possible that these other factors could.

In conclusion, past research suggests that choice can be powerful even without conferring actual control because it creates an illusion of control. Our research suggests a more sober perspective on the value of choice: Choice simply enables people to get what they want.

Empathy for joy recruits a broader prefrontal network than empathy for sadness; prefrontal cortex activation during both types of empathy was positively predicted by working memory capacity

Taiwo, Z., Bezdek, M., Mirabito, G., & Light, S. N. (2021). Empathy for joy recruits a broader prefrontal network than empathy for sadness and is predicted by executive functioning. Neuropsychology, 35(1), 90–102. https://doi.org/10.1037/neu0000666

Rolf Degen's take: https://twitter.com/DegenRolf/status/1346485527550320641

Abstract: Empathy encompasses the ability to contemplate and vicariously share in the emotional life of others, and is critical for social interaction, and may enhance subjective happiness.

Objective: While a few theoretical models propose that executive function may play a role in empathy, it is unknown how variation in executive function, and underlying variation in key large-scale brain network nodes, such as the dorsolateral prefrontal cortex node within the executive control network—or the medial prefrontal cortex (PFC) node within the mentalizing/theory of mind network—may account for individual differences in empathy capacity.

Method: The relationship between individual differences in executive capacity—parsed into working memory, inhibition, and cognitive flexibility subdomains—and magnitude of activity in a priori identified PFC subregions during a functional MRI-based ecologically valid empathy induction paradigm, was investigated. Empathic happiness (i.e., vicarious joy) and empathic concern (i.e., vicarious sadness) in response to the life circumstances of actual people were measured at separate time points as brain functional MRI was obtained. Participants also completed executive-heavy clinical neuropsychological tasks outside of the scanner.

Results: Frontopolar PFC was activated across both types of empathy. However, empathic happiness related to engagement of a much broader network of prefrontal cortex subregions relative to empathic concern: spawning frontopolar, dorsolateral, and medial aspects. PFC activation during both types of empathy was positively predicted by working memory capacity.

Conclusion: Activation in core aspects of the working memory-executive control network, and core happiness-related aspects of the mentalizing brain network (i.e., medial PFC and precuneus) predicted greater empathy capacity.

Documenting individual differences in the propensity to hold attitudes with certainty

DeMarree, K. G., Petty, R. E., Briñol, P., & Xia, J. (2020). Documenting individual differences in the propensity to hold attitudes with certainty. Journal of Personality and Social Psychology, 119(6), 1239–1265. https://doi.org/10.1037/pspa0000241

Abstract: The certainty with which people hold their attitudes is an important consideration because attitudes held with certainty better predict judgment and behavior than attitudes held with doubt. However, little is known about whether people’s assessments of their certainty reflect a disposition to hold attitudes with confidence. Adapting methods used to document individual differences in people’s attitudes, the present research demonstrates that the certainty with which people hold any given attitude is in part a reflection of a relatively stable disposition. Across 5 studies and 6 samples (total N = 106,050), we demonstrate dispositional variability in attitude certainty and show that it is related to but distinct from confidence in other judgmental domains. We also demonstrate that dispositional attitude certainty may be useful in predicting certainty in newly formed evaluations (Study 3) and an important consequence of certainty—attitude-behavior correspondence (as indicated by reports of behavioral intentions and recent behavior; Study 4 and Student Sample in Study 5). Furthermore, we demonstrate that dispositional attitude certainty is relatively stable over time (Study 5). Results are discussed with respect to potential mechanisms and boundary conditions relating to dispositional attitude certainty, the implications of these individual differences for attitudes and persuasion, as well as the potential origins of dispositional attitude certainty.

Women reported slightly more openness to uncommitted sexual relationships during the peri-ovulatory session, but significant differences were restricted only to women who exhibited the luteinizing hormone surge

Variation in sociosexuality across natural menstrual cycles: Associations with ovarian hormones and cycle phase. Urszula M. Marcinkowska et al. Evolution and Human Behavior, Volume 42, Issue 1, January 2021, Pages 35-42. https://doi.org/10.1016/j.evolhumbehav.2020.06.008

Abstract: The psychological construct of sociosexuality—one's sexual openness or propensity to engage in uncommitted sexual relationships—has been broadly examined within numerous cultures and mating contexts. Although there is some evidence suggesting that components of sociosexuality, namely behavior, desire and attitude, change within-person, relatively little research has investigated potential sources of such variation. The aim of our study was to explore if the individual components of sociosexuality change across the menstrual cycle, either as a function of cycle phase or ovarian hormones. One hundred and two naturally cycling women, both single and in a committed relationships, completed questions from the the SOI-R (Sociosexuality Revised) questionnaire three times during a menstrual cycle, scheduled to coincide with their early follicular, peri-ovulatory, and luteal phases. Women provided saliva samples and performed luteinizing hormone tests to distinguish between ovulatory and anovulatory cycles. Women reported slightly more openness to uncommitted sexual relationships during the peri-ovulatory session, but significant differences were restricted only to women who exhibited the luteinizing hormone surge. Ovarian hormone concentrations within cycles significantly predicted SOI Attitude and Desire scores, with estradiol positively related, and progesterone negatively related to openness to uncommitted sexuality. These effects were generally modest in size. The results of this study suggest that sociosexuality can vary within short periods of time, such as a single menstrual cycle.

Keywords: SociosexualitySOI-RMenstrual cycleLH testsEstradiolProgesteronePeri-ovulatory shifts

Baby falls while walking: We propose that a system that discounts the impact of errors in early stages of development encourages infants to practice basic skills such as walking to the point of mastery

The impact of errors in infant development: Falling like a baby. Danyang Han  Karen E. Adolph. Developmental Science, December 5 2020. https://doi.org/10.1111/desc.13069

Abstract: What is the role of errors in infants' acquisition of basic skills such as walking, skills that require immense amounts of practice to become flexible and generative? Do infants change their behaviors based on negative feedback from errors, as suggested by “reinforcement learning” in artificial intelligence, or do errors go largely unmarked so that learning relies on positive feedback? We used falling as a model system to examine the impact of errors in infant development. We examined fall severity based on parent reports of prior falls and videos of 563 falls incurred by 138 13‐ to 19‐month‐old infants during free play in a laboratory playroom. Parent reports of notable falls were limited to 33% of infants and medical attention was limited to 2% of infants. Video‐recorded falls were typically low‐impact events. After falling during free play in the laboratory, infants rarely fussed (4% of falls), caregivers rarely showed concern (8% of falls), and infants were back at play within seconds. Impact forces were mitigated by infants' effective reactive behaviors, quick arrest of the fall before torso or head impact, and small body size. Moreover, falling did not alter infants' subsequent behavior. Infants were not deterred from locomotion or from interacting with the objects and elevations implicated in their falls. We propose that a system that discounts the impact of errors in early stages of development encourages infants to practice basic skills such as walking to the point of mastery.

Modern women show signs of the ancestral competition among women, disliking & aggressing against those who threaten their romantic prospects, targeting especially physically attractive & sexually uninhibited peers

Our Grandmothers’ Legacy: Challenges Faced by Female Ancestors Leave Traces in Modern Women’s Same-Sex Relationships. Tania A. Reynolds. Archives of Sexual Behavior, Jan 4 2021. https://rd.springer.com/article/10.1007/s10508-020-01768-x

Abstract: Investigations of women’s same-sex relationships present a paradoxical pattern, with women generally disliking competition, yet also exhibiting signs of intrasexual rivalry. The current article leverages the historical challenges faced by female ancestors to understand modern women’s same-sex relationships. Across history, women were largely denied independent access to resources, often depending on male partners’ provisioning to support themselves and their children. Same-sex peers thus became women’s primary romantic rivals in competing to attract and retain relationships with the limited partners able and willing to invest. Modern women show signs of this competition, disliking and aggressing against those who threaten their romantic prospects, targeting especially physically attractive and sexually uninhibited peers. However, women also rely on one another for aid, information, and support. As most social groups were patrilocal across history, upon marriage, women left their families to reside with their husbands. Female ancestors likely used reciprocal altruism or mutualism to facilitate cooperative relationships with nearby unrelated women. To sustain these mutually beneficial cooperative exchange relationships, women may avoid competitive and status-striving peers, instead preferring kind, humble, and loyal allies. Ancestral women who managed to simultaneously compete for romantic partners while forming cooperative female friendships would have been especially successful. Women may therefore have developed strategies to achieve both competitive and cooperative goals, such as guising their intrasexual competition as prosociality or vulnerability. These historical challenges make sense of the seemingly paradoxical pattern of female aversion to competition, relational aggression, and valuation of loyal friends, offering insight into possible opportunities for intervention.

Supposedly, having multiple non-marital sex partners reduces traditional incentives for men to get married; instead, recent sex partners reduce the odds of marriage, but the lifetime number of non-marital sex partners does not

Wolfinger, Nicholas H., and Samuel Perry. 2021. “Does Promiscuity Affect Marriage Rates?.” SocArXiv. January 4. doi:10.31235/osf.io/n9e6p

Rolf Degen's take: https://twitter.com/DegenRolf/status/1346329239063293952

Abstract: Sociologists have proposed numerous theories for declining marriage rates in the United States, generally highlighting demographic, economic, and cultural factors. One controversial theory contends that having multiple non-marital sex partners reduces traditional incentives for men to get married and simultaneously undermines their prospects in the marriage market. For women, multiple partners purportedly reduces their desirability as spouses by evoking a gendered double-standard about promiscuity. Though previous studies have shown that having multiple premarital sex partners is negatively associated with marital quality and stability, to date no research has examined whether having multiple non-marital sex partners affects marriage rates. Data from four waves of the National Survey of Family Growth reveal American women who report more sex partners are less likely to get married (though so too are virgins). Yet this finding is potentially misleading given the retrospective and cross-sectional nature of the data. Seventeen waves of prospective data from the National Longitudinal Survey of Youth’s 1997 mixed-gender cohort that extend through 2015 show that more non-marital sex partners has a temporary effect on marriage rates: recent sex partners reduce the odds of marriage, but the lifetime number of non-marital sex partners does not. Seemingly unrelated bivariate probit models suggest that the short-term effect is likely causal. Our findings ultimately cast doubt on recent scholarship that has implicated the ready availability of casual sex in the retreat from marriage. Rather, the effect of multiple sex partners on marriage rates is “seasonal” for most Americans.

A 44-year-old woman started to ask whether her family had attended her funeral; since she thought she had died, she told her husband to marry another woman

Cotard syndrome in anti-NMDAR encephalitis: two patients and insights from molecular imaging. J Ramirez Bermudez et al. The Neural Basis of Cognition, Jan 4 2021. https://doi.org/10.1080/13554794.2020.1866018

Rolf Degen's take: https://twitter.com/DegenRolf/status/1346129241281339398

Abstract: Cotard syndrome is a clinical condition defined by the presence of nihilistic delusions. We report two patients with Cotard syndrome in whom anti-NMDAR encephalitis (ANMDARE) was confirmed. Both cases showed features of affective psychosis, developed catatonic syndrome, and worsened after the use of antipsychotics. 18F-FDG PET brain studies showed a bilateral hemispheric pattern of hypometabolism in posterior regions, mainly in the cingulate cortex and in the medial aspects of parietal and occipital lobes. A more severe hypometabolism was observed in the right hemisphere of both patients. Both cases remitted with the use of specific immunotherapy for ANMDARE.

KEYWORDS: Cotard syndromenihilistic delusionsanti-NMDAR encephalitisautoimmune encephalitismolecular imaging

This paper proposes that ancestral use of irrigation increases autocracy and a culture of collectivism, & reduces contemporary female labor force participation and female property rights

Fredriksson, Per G.; Gupta, Satyendra Kumar (2020): Irrigation and Culture: Gender Roles and Women’s Rights, GLO Discussion Paper, No. 681, Global Labor Organization (GLO), Essen. https://www.econstor.eu/bitstream/10419/225005/1/GLO-DP-0681.pdf

Abstract: This paper proposes that ancestral use of irrigation reduces contemporary female labor force participation and female property rights. We test this hypothesis using an exogenous measure of irrigation and data from the Afrobarometer, cross-country data, the European Social Survey, the American Community Survey, and the India Demographic and Household Survey. Our hypothesis receives considerable empirical support. We find negative associations between ancestral irrigation and actual female labor force participation, and attitudes to such participation, in contemporary African and Indian populations, 2nd generation European immigrants, 1.5 and 2nd generation US immigrants, and in cross-country data. Moreover, ancestral irrigation is negatively associated with attitudes to female property rights in Africa and with measures of such rights across countries. Our estimates are robust to a host of control variables and alternative specifications. We propose multiple potential partial mechanisms. First, in pre-modern societies the men captured technologies complementary to irrigation, raising their relative productivity. Fertility increased. This caused lower female participation in agriculture and subsistence activities, and the women worked closer to home. Next, due to the common pool nature of irrigation water, historically irrigation has involved more frequent warfare. This raised the social status of men and restricted women’s movement. These two mechanisms have produced cultural preferences against female participation in the formal labor market. Finally, irrigation produced both autocracy and a culture of collectivism. These are both associated with weaker female property rights.

JEL Codes: J16, J21, N50, O10, P14, Q15, Z13.

Keywords: Irrigation; agriculture; culture; gender; norms; labor force participation; property rights.

5. Possible Mechanisms

In this section, we discuss possible mechanisms for the effect of irrigation potential on

female labor force participation and female property rights, respectively.

5.1. Female participation on pre-industrial agriculture

Boserup (1970) argues that males have historically captured technologies complementary

to irrigation, which increased their productivity in irrigated agriculture. Women worked with

less advanced technology and were relatively less productive. Irrigation activities may also be

dangerous (including to accompanying children), and may involve confrontations with

neighbors over water allocation. These factors all contribute to male labor specialization in

irrigated agriculture. While women still worked in agriculture to some degree, their work

gravitated toward the homestead, e.g. specializing in processing cereals and child care,

spending their lives mainly indoors or in the courtyard with little contact with non-relatives

(Ember, 1983).20

The Standard Cross-Cultural Sample (SCCS), compiled by Murdock and White (1969), has

data from 186 separate pre-industrial societies.21 The Ethnographic Atlas by Murdock (1967)

has data on 1,267 pre-industrial societies from around the world. The Atlas contains little

information about the societies themselves, however. The measure of the female-relative-tomale participation in overall agricultural production takes values from 1 to 5, where relative

participation is coded as follows. 1: males exclusively; 2: males predominantly; 3: equally; 4:

females predominantly; and 5: females exclusively. The dependent variables. The measure of

the relative time and effort spent on subsistence activities by females varies from 1 to 3, where

1: men expend more; 2: men and women expend roughly equal; 3: women expend more.

While the SCCS and the Atlas contain information on the centroid of each society, the

measurement of the precise location may involve errors. Moreover, information about the land

area covered by these pre-industrial societies is missing. We use a buffer zone of 200 km

around the centroid in order to construct the measure of irrigation potential and control

variables (Alesina et al., 2013). The ethnographic controls include suitability of the local

environment for agriculture, the presence of large domesticated animals, the proportion of the

local environment that is tropical or subtropical, an index of settlement density, and an index

of political development.

The mean variable values are provided in the table heading of Table 6. While column (1)

uses data from the Ethnographic Atlas, the remaining columns use SCCS data. Columns (1)-

(4) use female overall participation in agriculture as outcome variable, column (5) studies the

overall relative female contribution to subsistence in time and effort, and columns (6)-(8)

provide estimates for crop tending, harvesting, and milking, respectively. All columns include

fixed effects for the century-of-observance and language, ethnographic controls including plow

use, suitability of the local environment for agriculture, the presence of large domesticated

animals, the proportion of the local environment that is tropical or subtropical, economic

complexity, and political development.

Column (1) irrigation potential has a negative and statistically significant influence on

relative female participation in agricultural activities overall. The effect of moving from zero

to complete irrigation potential equals -1.45, which is substantial given the 3.04 mean. The

effect is stronger in column (2), using SCCS data. Column (3) adds a dummy for whether

cereals are the main crops, which Ember (1983) and Hansen et al. (2015) suggest influences

female labor force participation. The coefficient on irrigation potential rises further. Column

(4) controls for societies with formal class stratification systems, where males may be less

likely to participate in agricultural field work. The two added controls are insignificant, while

irrigation potential remains significant. Column (5) suggests that the female relative

contribution to subsistence activities were lower in societies with greater irrigation potential.

This reflects a shift away from agricultural field activities towards greater domestic and child

rearing duties. Columns (6)-(7) provide evidence that irrigation is associated with a decline in

female participation in some important agricultural activities outside the home, while column

(8) suggests the opposite effect occurred to milking which occurs closer to home. Table C5 in

online Appendix C provides cross-country OLS evidence that irrigation is associated with

restrictions on women’s freedom of movement within a country, using data from Coppedge et

al. (2019).

Overall, the results are consistent with women staying closer to the homestead in irrigated

areas during the pre-industrial time period. This suggests one possible partial mechanism which

links irrigation to lower contemporary female labor force participation rates and related

attitudes. The division of labor appears to have persisted through intergenerational cultural

transmission. [Table 6]

5.2. Warfare

Irrigation water is frequently a common pool resource. Since water consumption by

upstream communities may affect consumption by downstream communities, especially in

times of drought, conflicts are likely to occur. Anecdotal evidence includes Iraq and the

Andes.22 Irrigation agriculture also led to a storable surplus and relatively more valuable land,

providing incentives for raids and external warfare by other groups (e.g., Ember, 1982; Ang

and Gupta, 2018). We hypothesize that irrigation societies had a greater incidence of violent

external conflict. This yielded a greater demand for men due to greater muscle strength and

aggressiveness, improving their social standing (Chagnon, 1988; Ramos-Toro, 2019). RamosToro (2019) provides evidence of a negative relationship between exposure to conflict and

contemporary female labor force participation.23 Warfare may also have been associated with

reduced female mobility, and stricter social norms and restrictions on women’s labor market

participation outside the home.

Table 7 provides some support for this hypothesis. Columns (1)-(3) utilize society level

data from the SCCS (Murdock and White, 1969), while columns (4)-(9) use historical district

level data from India. The dependent variable in column (1) is a measure of external warfare.

We focus on societies with agricultural activities. We recode the Murdock and White (1969)

external warfare measure as follows: it takes a value of 1 if external war is ‘frequent, occurring

at least yearly’ or ‘common, at least every five years’; it takes a value of zero if ‘occasional, at

least every generation’ or ‘rare or never’. The sample size declines to 54. This renders language

and century fixed effects and the inclusion of tropical climate infeasible in this analysis. The

results should thus be interpreted with these drawbacks in mind. The logit model in column (1)

suggests that irrigation potential is positively associated with external warfare. Columns (2)-

(3) present ordered logit regressions. Column (2) is the basic model from Table 1 with female

participation in overall agriculture as the outcome variable (but with a smaller sample size).

External warfare is negative and significant in column (3), while the irrigation potential point

estimate declines modestly (in absolute value) from -2.00 to -1.67. This provides some support

for the hypothesis that a history of external warfare a partial channel between irrigation and

female participation in agriculture in pre-industrial societies.

Columns (4)-(9) provide district level evidence from India in support of the proposed

warfare mechanism. In rural India, most households working outside the home are engaged in

agricultural sector work (Kapsos et al., 2014). We measure female employment outside the

home by the ratio of the population of female agricultural workers to the total female population

in year 2011. In column (4), war count is a measure of the total number to land battles over

years 610-1962 occurring within a distance of 50km from the district, geocoded using Jacques

(2007).24 In column (7), the period of observations for war count is instead restricted to 1001-

1867AD. Jacques (2007) records relatively few instances of wars before 1001 (data quality

may be an issue), and in 1858 the British Crown took over the administration of India from the

British East India Company. The wars for accession of the native states ceased after 1857.

Columns (4) and (7) present negative binominal regressions, while columns (5), (6), (8), and

(9) are generalized linear model regressions. Geographical controls (temperature, precipitation,

latitude, area, land quality, and nightlight luminosity) and language fixed effects (largest

language group within the district, reflecting cultural variation across districts) are included.

One benefit of using data on India is the low interstate migration rate, which maintains longterm cultural differences (Kone et al., 2018).

Column (4) suggests a positive association between a district’s irrigation potential and the

historical experience with wars. When war count is included in column (6), the (absolute value

of the) irrigation potential point estimate declines relative to column (5), from -0.137 to -0.115,

while war count is negative and significant. The takeaway from columns (7)-(9) is similar.

These findings provide some support for the hypothesis that a history of warfare is a possible

partial mechanism linking irrigation and female participation in agriculture in contemporary

India. [Table 7]

5.3. Autocracy

Next, we provide evidence that historical irrigation may affect contemporary female

property rights regimes via an autocracy channel. Underpinned by resource curse theory,

Bentzen et al. (2017) argue that historical irrigation agriculture raised the likelihood that a preindustrial society was ruled by an elite based on the control of a natural resource. This has

yielded lower levels of contemporary democracy. Autocracies have weaker property rights

(Gradstein, 2007), and Fish (2002) suggests that authoritarianism is associated with negative

outcomes for women.25

To study the determination of female property rights, we utilize the standard general

measures of democracy, Polity2. The male political majority (in both democracies and

autocracies) is likely to determine the extent of female property rights. Table 8 shows that

democracy works as channel for the effect of irrigation potential on contemporary female

property rights. Column (1) establishes that irrigation potential has a negative effect on

democracy, measured by Polity2. In column (2), irrigation potential has a negative effect on

female property rights as shown above, but this effect disappears when we include democracy

in column (3). This suggests that the effect of irrigation on female property rights works at least

partially through the democracy channel. In contrast, while democracy has a positive

association with male property rights in column (5), there is no evidence that democracy works

as a link between irrigation and male property rights. [Table 8]

Table C6 in the online appendix provides additional evidence that attitudes, actual female

political participation rates, and the freedom to discuss politics are negatively associated with

irrigation potential. The first column uses a statement from the Afrobarometer as outcome

variable, and the remaining three columns use variables from Coppedge et al. (2019). 26

5.4. Individualism vs. Collectivism

This section investigates the cultural dimension of individualism vs. collectivism as a

possible potential mechanism. Buggle (2020) finds that irrigation is negatively correlated with

individualism, because irrigation required constant collaboration which yielded collectivism.

Gorodnichenko and Roland (2017) argue that the degree of individualism influences societies’

institutional choices. In particular, they find that individualism has a positive association with

the level of protection against expropriation risk, a measure of property rights. Binder (2019)

reports that collectivism is correlated with a belief in traditional gender roles.

Table 9 explores whether individualism vs. collectivism may function as a partial channel

between irrigation potential and contemporary female property rights. We use Hofstede et al.’s

(2010) measure of individualism and Coppedge et al.’s (2019) measure of property rights.

Irrigation potential has a negative correlation with individualism in column (1) and with female

property rights in column (2). This effect declines moderately (in absolute value) when

individualism is entered in column (3), from -1.75 to -1.64. However, a similar pattern occurs

for male property rights in columns (4) and (5), from -1.67 to -1.57. It appears that the

individualism vs. collectivism dimension of culture may provide a partial link between

irrigation potential and property rights for both genders. Thus, we do not find strong evidence

that this link is stronger for female than for male property rights. To investigate this further,

Table C7 in the online appendix includes both individualism and democracy as potential

mechanisms. It appears that both mechanisms work for female property rights, but only

democracy constitutes a channel for male property rights. [Table 9]

Taste is afforded the greatest relevance to nutrition as it is posited to have improved the probability of survival, helping screen safe and potentially toxic properties of foods; this teleology is dubious

Taste, teleology and macronutrient intake. Richard D Mattes. Current Opinion in Physiology, Volume 19, February 2021, Pages 162-167. https://doi.org/10.1016/j.cophys.2020.11.003

Abstract: Among the human sensory systems, taste is afforded the greatest relevance to nutrition as it is posited to have aided the identification and ingestion of nutrients in the environment and thereby improved the probability of survival. With respect to the macronutrients, sweet, umami and oleogustus (fat taste) reportedly facilitated meeting energy, essential amino acid and essential fatty acid requirements. However, such a teleological view fails to account for the fact that humans are largely blind to the primary sources of the macronutrients in the environment (starch, protein and triacylglycerol) and, in the case of protein and fat, the effective taste stimuli are generally unpleasant degradation products. Additional challenges to the prevailing teleology are also presented. Some have proposed that the sense of taste serves as a palatability screen that functions more basically by signaling safe and potentially toxic properties of potential foods. However, it is well documented that sensory qualities are unreliable predictors of food safety (sweet foods can be toxic and bitter foods nutritious). Instead, it is proposed that taste contributes to food choice by acquiring predictive information about wholesomeness through innate and learned mechanisms.

Sweet taste

Humans are limited to carbohydrates, fats and proteins as substrates to meet energy needs. Knowledge of the composition of ancient human diets is incomplete, but recent evidence supports a substantive contribution of starchy foods in many pre-agricultural populations [12] though it likely varied widely between subpopulations [13]. Access to simple carbohydrates would have been extremely low [14].

A functional role for sweet taste is forcefully made by reduced conservation of the sweet taste receptor and evidence of insensitivity to this quality by vertebrates not exploiting sweet foodstuffs (e.g. cats, sea lions, whales, pandas, horses, western clawed frog, vampire bats) as well as reemergence of sensitivity by hummingbirds who are exclusive nectar feeders while other birds lack this capability and food choice [15•,16,17••]. However, a broader analysis reveals a lack of association between losses of sweet taste sensitivity and diet [17••].

There are multiple additional observations that challenge the view that sensitivity to sweetness would be a functional mechanism to access carbohydrate. First, there is no essential mono or disaccharide and those are the predominant effective sweet taste stimuli. Thus, sweet taste is not tuned to an essential nutrient. Second, sources of sweet carbohydrate were extremely rare in the environment throughout most of human evolution. With the exception of limited access to honey and seasonal fruits, a receptor tuned to simple sugars would have served little purpose post-weaning. Even its role in promoting milk ingestion pre-weaning is uncertain. Fat is the primary determinant of the energy density of breast milk and studies with gruels varying in energy density and sweetness reveal intake is more closely related to energy density [18]. Also, interestingly, kittens who are carnivores and lack a functional sweet receptor nurse effectively [19] on mature cat milk that is approximately 4% lactose and only 6.3–8.6% protein [20]. Third, a more functional taste contribution to locating and promoting carbohydrate intake would have been sensitivity to starch which was abundant. There is preliminary evidence of human sensitivity to short chain oligosaccharides of 7 and 14 units (not 44) [21], but the sensation is not mediated by the T1R2–T1R3 (sweet) receptor and the sensation they evoke is not sweetness.

Further, it is clear that sweetness is an imperfect indicator of safe and available carbohydrate as sweet fruits are not necessarily rich sources of carbohydrate or energy (i.e. they have low energy density due to their high water content), not all sweet stimuli are carbohydrate (e.g. Monellin, Thaumatin, Brazzine are proteins) and some sweet molecules are toxic (e.g. lead acetate).

In summary, sweetness lacks the sensitivity and specificity to identify and promote the consumption of wholesome carbohydrates in the environment. However, it is not disputed that sweetness is rewarding and an appetitive signal that promotes feeding generally [18,22,23].

Umami taste

Proteins are comprised of amino acids, nine of which are considered essential that is, cannot be synthesized in humans so must be acquired from the diet. Rarely are free amino acids encountered in the environment because protein synthesis is extremely efficient. Amino acids are synthesized when needed to build proteins and in requisite proportions. Proteins play many roles in the body. They serve as enzymes, hormones, neurotransmitters, nutrient transporters, structural elements and are crucial for growth and development, pH balance, fluid balance, immune function and when consumed in excess of need, can provide energy.

Given these multiple essential roles, a teleological view would support a sensory system tuned to protein sources in the environment. However, the importance of taste in this regard is questionable. Some evidence suggests taste alone allows rapid identification of dietary protein sources in protein-depleted rats [24], but the preponderance of evidence indicates selection in rodents and other animals depends on post-ingestive learning where the sensory signal only acquires predictive power based on an association with a corrective post-ingestive outcome [25,26]. Second, a number of essential amino acids are effective taste stimuli, but a number of these elicit unpleasant sensations (e.g. methionine, leucine, tryptophan) and render protein hydrolysates unpalatable. This would discourage ingestion of the required nutrient.

The more specific case of Umami taste has attracted considerable attention. The prototypical stimulus for Umami taste is monosodium glutamate (MSG). Psychophysical studies in infants [27] and adults [28] indicate the stimulus is rejected when presented in water. In suprathreshold concentrations the quality of D-MSG is soapy-metalic and L-MSG is described as predominantly bitter [29], generally negative qualities. It is only in selected food contexts that it contributes a positive quality [30] and then this is augmented by the co-presence of 5′ ribonucoleotides [31]. Despite the low palatability of MSG, the teleological argument has been made that sensitivity to the compound signals the presence of protein sources in the environment and presumably the desirability of consuming them [32••]. Consistent with this view, herbivores generally lack the umami taste receptor [16]. However, the necessity of this signaling system is not supported. Selected animals have lost taste responsivity to umami (e.g. pig, horse, rabbit, tree shrew, mouse lemur, marmoset, tarsier, hyrax, sea lion, bottlenose dolphin) but all animals require protein [17••,33]. Additionally, if the teleological perspective that umami sensitivity aids acquisition of needed protein is true, individuals with low or marginal protein status should exhibit augmented hedonic responses to MSG containing foods. Heightened hedonic responses to other nutrients during periods of deficit have been documented [34]. While there is a report to this effect [35] for protein, the broader literature is not supportive [28,36]. Indeed, palatability is diminished in this state and is relatively heightened in the protein replete state [32••], counter to the hypothesis. An additional teleological argument holds that there would have been a survival benefit of detecting and consuming purine-rich foods which would contain higher concentrations of ribonucleotides. These foods can lead to elevated uric acid concentrations with consequent physiological responses that could have mitigated famine-related threats to survival [37]. If true, then, it is problematic now where famines are less common and diseases of overconsumption predominate, including gout, hypertension and glucose intolerance. If gustatory wisdom held in this case, it appears to have been lost or rendered non-functional in the current environment.

Taken together, the evidence indicates food choices related to satisfying protein requirements are guided more by non-protein specific signals that become associated with post-ingestive cues that protein needs are met and umami taste, in particular, serves to promote the overall palatability of the diet and thereby encourages food intake generally [38].

Fat taste (Oleogustus)

Linoleic acid and alpha-linolenic acid (ALA) are essential fatty acids (EFA) for humans, that is, they cannot be synthesized in the body and must be obtained via the diet. Eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) can be synthesized from ALA, but the conversion efficiency is low so a dietary source is beneficial. These fatty acids serve multiple purposes in the body. They have anti-inflammatory activity, are structural elements in cell membranes and are precursors to a range of bioactive compounds. Additionally, fats, in general, are the most energy dense macronutrient. Thus, a system to detect them and promote their consumption would hold survival value.

Though there have been isolated claims that there is a taste for fat, this view received little empirical support until recently [39••]. The predominant signals from dietary fat were considered visual, somatosensory and olfactory. The somatosensory contribution from triacylglycerols, the predominant form of dietary fat, include sensations such as creaminess, viscosity, lubricity, and mouth-coating and are largely rated as appetitive (i.e. palatable). In contrast, the olfactory cues, stemming primarily from free fatty acids (FFA) derived from triacylglycerol, are largely considered aversive. Consequently, for most foods, concentrations of free fatty acids are purposefully held below detection thresholds during product development. Of course, through experience even strong fat-based odors can acquire a positive valence. Work demonstrating dietary fat can elicit an early spike in plasma triacylglycerol concentrations when somatosensory and olfactory cues were largely controlled, suggested a role for taste [40]. Studies in mice indicate FFA, not triacylglycerol, are the effective taste stimuli [41]. Subsequent studies documented measurable and differential taste threshold for various fatty acids [42] in humans and the qualities appear to change with fatty acid chain length. Short-chain fatty acids are largely sour (<C:6) while longer chain fatty acids (>C:16) evoke an unpleasant sensation that is unique from other primary taste qualities [43] and has been termed oleogustus. The essential fatty acids are consistently rated as unpleasant. They would be encountered in the environment largely through rancid foods and it has been posited that they act more as warning signals than appetitive signals. This is inconsistent with a teleological perspective that the function of oleogustus is to aid in the acquisition of EFA and/or energy. Indeed, it has further been proposed that high fat intake occurs because of insensitivity to the taste of fatty acids [44]. There is the possibility that the taste of low concentrations of long-chain FFA could contribute positively to the overall flavor profile of some foods, just as bitter notes, unpleasant in isolation, contribute to the palatability of selected foods (e.g. wines, chocolate, coffee). Of course, if one accepts this caveat, it is also true that bitterness cannot be regarded as a uniformly aversive signal protecting against toxin exposure.

Whether oleogustus qualifies as a taste primary is not settled science. If it is accepted, the effective taste stimulus would most likely occur in rancid foodstuffs. The quality of the sensation would discourage ingestion and hinder meeting EFA and energy needs.