Bitterness and Food Rejection

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:

• care
• cooperation (Boyd & Richerson, 2022)
• inequality aversion (Brosnan & Waal, 2014)
• balance authority vs autonomy (Wengrow & Graeber, 2018)^[3]
• discern impurity (Atari et al., 2022)

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

References

Endnotes