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Bitterness and Food Rejection

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Notes

I do not have an alternative to Greene et al’s theory, but there are some steps which may take us towards constructing one.

Step 1: Change the Question

Greene et al arrive at their theory by asking a question about responses to sacrificial dilemmas:

‘We developed this theory in response to a long-standing philosophical puzzle known as the trolley problem’ (Greene, 2015, p. 203; see Greene, 2023)

A problem for this starting point is that there appear to be confounds in the dilemmas that give rise to trolley problems. Indeed, the mixed pattern of evidence for and against Greene et al’s theory might be explained by their choice of vignettes using trolley cases as stimuli. Waldmann, Nagel, & Wiegmann (2012, p. 288) offers a brief summary of some factors which have been considered to influence responses including:

  • whether an agent is part of the danger (on the trolley) or a bystander;
  • whether an action involves forceful contact with a victim;
  • whether an action targets an object or the victim;
  • how far the agent is from the victim;[1] and
  • how the victim is described.

Other factors include whether there are irrelevant alternatives (Wiegmann, Horvath, & Meyer, 2020); and order of presentation (Schwitzgebel & Cushman, 2015).

They comment:

‘A brief summary of the research of the past years is that it has been shown that almost all these confounding factors influence judgments, along with a number of others [...] it seems hopeless to look for the one and only explanation of moral intuitions in dilemmas. The research suggests that various moral and nonmoral factors interact in the generation of moral judgments about dilemmas’ (Waldmann et al., 2012, pp. 288, 290).

For proponents of Greene et al’s view, this might be taken as encouragement. Yes, the evidence is a bit mixed. But perhaps what appears to be evidence falsifying predictions of the view will turn out to be merely a consequence of extraneous, nonmoral factors influencing judgements.

Alternatively, Waldmann et al.’s observation could be taken to suggest that few if any of the studies relying on dilemmas presented in vignette form provide reliable evidence about moral factors since they do not adequately control for extraneous, nonmoral factors. As an illustration, Gawronski, Armstrong, Conway, Friesdorf, & Hütter (2017) note that aversion to killing (which would be characteristically deontological) needs to be separated from a preference for inaction. When considering only aversion to killing, time pressure appears to result in characteristically deontological responses, which would support Greene et al’s theory (Conway & Gawronski, 2013). But when aversion to killing and a preference for inaction are considered together, Gawronski et al. (2017) found evidence only that time pressure increases preferences for inaction.

While the combination of mixed behavioural evidence and methodological challenges associated with using dilemmas presented in vignettes does not provide a case for rejecting Greene et al’s view, it does motivate considering fresh alternatives.

Step 2: Distinguish Ethical Abilities

Greene et al’s theory treats ethical abilities as all explained by a single fast process and a single slow process. Supporting this is a premise about ethical abilities having a single function:

‘morality is a suite of cognitive mechanisms that enable otherwise selfish individuals to reap the benefits of cooperation.’ (Greene, 2015, p. 198)

Others suggest that different ethical abilities have different functions (for example, Haidt & Graham, 2007). In particular, concerns about purity are probably distinct from concerns about harm (Chakroff, Russell, Piazza, & Young, 2017).[2]

The diversity of ethical abilities indicates that they may not all have one function:

I will focus on purity.

Step 3: Find a Non-ethical Model

To guide our thinking, it is useful to have a non-ethical case which is well understood and in which attitudes and behaviours are decoupled.

To this end, consider food-rejection behaviours.

All animals need to balance the need to eat enough of the best available foods against the risk of ingesting toxins. To this end, they exhibit complex pattern of food-rejection behaviours.

Food-rejection behaviours can be driven by attitudes about poison (for example, you may know something about the origins of a food that otherwise appears delicious). But they can also be driven by aversion to bitterness. Importantly, this can occur independently of, and even counter to, your attitudes.

Bitterness

How does aversion to bitterness work? Poisonous foods are often bitter. Although the correlation between bitterness and toxicity is not super strong and bitter things can be beneficial (such as caffeine, for example), there is broad consensus that avoiding poisons is one of the functions of sensitivity to bitterness (Nissim, Dagan-Wiener, & Niv, 2017). Animals who encounter a greater proportion of poisonous foods in their normal diet (herbivores) show both higher sensitivity to bitterness (Li & Zhang, 2014) and a higher tolerance for it (Ji, 1994). This makes sense because herbivores need to take more risks: they could not get enough to eat if they rejected everything bitter. Further, two changes in diet which reduce exposure to toxins, namely eating more animals or cooking with fire, may have gradually reduced sensitivity to bitterness (Wang, Thomas, & Zhang, 2004).

Bitterness appears innately aversive. A range of animals including sea anemones become averse to a food type after a single bitter encounter (Garcia & Hankins, 1975). In rats, ‘[t]he modal elicitor of aversive behaviours is a bitter, normally avoided substance like quinine, which evokes chin rubs, gapes, face washes, forelimb flails, and paw treads’ (Forestell & LoLordo, 2003, p. 141; Grill & Norgren, 1978). And in humans mixing a neutral flavour (vanilla, for example) with a bitter substance can reduce liking for that flavour (Baeyens, Crombez, De Houwer, & Eelen, 1996; Dickinson & Brown, 2007).

This suggests a minimal model for toxicity. Instead of a special-purpose learning mechanism, what is needed is just for bitter things to be aversive. With aversion to bitterness in place, ordinary learning mechanisms will reduce exposure to bitter things.[4]

Not everything bitter is bad. As well as indicating toxicity, bitterness is also associated with medicinal properties. Nissim et al. (2017) suggest that animals may exploit this association by eating bitter substances when ill. To illustrate, chimpanzees suffering from diarrhoea and other symptoms of parasite infection extract and chew an extremely bitter pith, which appears to improve their health (Huffman, 2001, p. 939).

Disgust

I suggest that food-rejection behaviours are a useful (if limited) model for thinking about purity-related behaviours.

Purity solves a problem: play and exploration bring many benefits, but can also increase the risk of exposure to pathogens. Concerns about purity seem to function to reduce the risk of exposure to pathogens (Atari et al., 2022; van Leeuwen, Park, Koenig, & Graham, 2012).

Following the food-rejection model, we can compare bitterness to disgust.[5] Disgust has a function linked to disease-avoidance (Oaten, Stevenson, & Case, 2009). And disgust can drive at least some purity-related behaviours—and even some attitudes (R. Wang, Yang, Huang, Sai, & Gong, 2019).

The analogy is limited by the complexity of disgust (see, for example, Tybur, Lieberman, Kurzban, & DeScioli, 2013).

Just here an objection arises: behaviours driven by disgust are not intrinsically ethical at all. There is, therefore, no possibility of using them to explain ethical decoupling.

Step 4: Borrow an Idea about Normativity

To reply to the above objection, we need to identify a sense in which some disgust driven behaviours are intrinsically ethical.

Normativity is a mark of the ethical:

‘When it comes to morality, the most basic issue concerns our capacity for normative guidance: our ability to be motivated by norms of behavior ...’ (FitzPatrick, 2021)

But how to get normativity into the picture? Michael and Butterfill (in preparation) offer the notion of a minimal norm. This is a pattern of behaviour which exists in part because of others’ responses to behaviors which conform to, or violate, the pattern; where these responses have the purpose of upholding conformity to the pattern.

Where disgust underpins purity-related minimal norms, we have intrinsically ethical behaviour.

And because digust can underpin purity-related minimal norms independently of normative attitudes, we have ethical decoupling..

Glossary

trolley cases : Scenarios designed to elicit puzzling or informative patterns of judgement about how someone should act. Examples include Trolley, Transplant, and Drop. Their use was pioneered by Foot (1967) and Thomson (1976), who aimed to use them to understand ethical considerations around abortion and euthanasia.

References

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Endnotes

  1. After this review was published, Nagel & Waldmann (2013) provided substantial evidence that distance may not be a factor influencing moral intuitions after all (the impression that it does was based on confounding distance with factors typically associated with distance such as group membership and efficacy of action). ↩︎

  2. Not everyone accepts this claim (Schein, Ritter, & Gray, 2016). ↩︎

  3. Wengrow & Graeber (2018) describe two groups, one of which eschewed slavery, the other of which used it in a complex hierarchical society. ‘If the ethics of their Californian neighbors bore comparison with mercantile values in early modern Europe, those of the Northwest Coast more closely resembled the aristocratic values of high feudalism. Societies comprised household estates divided into hereditary ranks of nobles, commoners, and slaves. Slaveholding was a defining attribute of nobility , and from Alaska south to W ashington state, intergroup slave raids were endemic. Nobles alone enjoyed the ritual prerogative of engaging with guardian spirits who conferred access to prestigious titles, which defined the legal contents of an estate. Commoners voluntarily provided labor and services to noble kin, who vied for their allegiance by offering spectacular feasts, entertainment, and the pleasure of vicarious participation in heroic exploits.’ (Wengrow & Graeber, 2018, p. 239) ↩︎

  4. There is a question about special-purpose learning mechanisms for flavour; see (Dickinson & Brown, 2007, p. 42): ‘The important point about this parallel between human evaluative conditioning and rat aversion conditioning for flavors lies with the issue of whether these forms of conditioning engage nonstandard learning processes. It is generally agreed that flavor aversion conditioning shows all the main phenomena of Pavlovian conditioning (Revusky, 1971), including blocking (Gillan & Domjan, 1977), and, therefore, the fact that two forms of conditioning can be dissociated in terms of their effective conditioned stimuli and response measures does not necessary imply that they recruit learning processes that operate according to differ- ent principles. It may well be that evaluative conditioning and contingency learning are mediated by dissociable systems but that both these systems are governed by similar principles. The critical test of whether pretraining a flavor as a predictor of the sugar or tween would block evaluative conditioning to another flavor during compound flavor training remains to be examined.’ ↩︎

  5. It’s just possible that there is a much closer connection between bitterness and ethical behaviours. In adults at least, unfairness can also sensations of bitterness. See Chapman, Kim, Susskind, & Anderson (2009), who establish that (1) responses to bitterness are marked by activation of the levator labii muscle ‘which raises the upper lip and wrinkles the nose’; (2) bitter responses are made not just to bitter tastes but also to ‘photographs of uncleanliness and contamination-related disgust stimuli, including feces, injuries, insects, etc.’; and (3) in a dictator game, ‘objective (facial motor) signs of disgust that were proportional to the degree of unfairness they experienced.’ If Chapman et al. (2009) are right that a limited but useful range of moral violations can produce bitter sensations, general-purpose learning mechanisms could produce aversion to actions that generate these moral violations. ↩︎