Preamble

Differences in the intensity of valenced experience across species may affect the proportion of resources we ought to allocate to helping different types of animals. I recently wrote a long report on this topic. (You can view a PDF of the report here.^[1]) In this summary, I attempt to more succinctly convey my main conclusions.

Main Text

We all know that some experiences feel good, while other experiences feel bad. In the jargon, we can say that experiences often take on a valence: an overall positive or negative flavor. We also know that some good experiences feel better than others, and some bad experiences feel worse than others. We can call these degrees the intensity of an experience.

Human lives are full of an assortment of valenced experiences of varying intensities. The difference between a person’s most positive experience and most negative experience is the person’s realized intensity range of valenced experience. But some individuals realize wider intensity ranges than others. Zooming out, we can describe the characteristic intensity range of a representative human being.

Are there differences in the characteristic intensity ranges of valenced experience across species? This question is important because the answer to it could affect the way we wish to spend our scarce resources helping different types of animals, including humans. For example, if the pains and pleasures of trout and salmon are but pale reflections of the pains and pleasures of cows and pigs, then in many instances we may be able to do more good helping mammals rather than fish.

I identified a three-stage approach to tackling this question:

1. Start with theoretical evolutionary biology. Reflecting on the evolutionary function of valenced experience could help us discern rough limits on what the intensity range of a species might look like.
2. Next, think about how cognitive and emotional traits contribute to the intensity of valenced experience. If we can get a handle on the role that cognition and emotion play, then we may be able to use differences in cognitive and emotional capacities as rough guides to differences in intensity range.
3. Finally, examine the potential neurobiological, behavioral, and physiological markers of the intensity of valenced experience. Researchers have been working for decades to validate objective metrics of pain intensity in humans. If successful, we could perhaps extend these metrics to nonhuman animals, thus offering a chance to measure the intensity of valenced experience directly.

My results are full of uncertainty. I combed through hundreds of studies and papers but struggled to piece together a coherent picture of the state of our knowledge. At times, it felt like I needed to be an expert in half a dozen distinct disciplines just to make sense of all the data I had collected. In the end, I arrived at a handful of tentative conclusions, two of which may be relevant to the way we allocate resources to interventions targeting different types of animals.

Tentative Conclusion #1: Humans and other mammals likely share a similar intensity range

The neurobiological machinery that controls human pain and pleasure sensitivity, as well as our basic emotional responses, is evolutionarily ancient, and therefore likely conserved across all mammals. From a behavioral, physiological, and neurological perspective, there is nothing uniquely human about bodily pains and pleasures. What’s more surprising is that from the same behavioral, physiological, and neurological perspective, there appears to be nothing uniquely human about our basic emotional responses. Other mammals probably feel fear, anger, anxiety, and sadness. Positive emotions appear equally widespread, with pretty robust analogues of (maternal) love and even friendship seemingly common among mammals. When the relevant behavior is similar, the physiological changes associated with the behavior are similar, and the neurobiology that presumably governs the behavior is similar, the most reasonable conclusion is that the emotional lives of nonhuman mammals are, in most respects, approximately as intense as the emotional lives of humans.

Tentative Conclusion #2: It appears unlikely that any species possesses an intensity range that is exclusively extraordinarily mild

Although it’s plausible that there are big differences in intensity range across species, I’m doubtful there exist any animals with the capacity for valenced experience whose intensity range exclusively vacillates so close to neutral as to be undeserving of our moral concern.

Sometimes people suggest that even if insects or crustaceans are sentient, these animals don’t merit much moral attention because even their most intense pains and pleasures are so faint as to be hardly noticeable. My research suggests that there is currently little evidence to support this claim, and at least provisional reason to reject it. For one, we aren’t in a position to conclusively rule out the possibility that insects and crustaceans have characteristically more intense experiences than more typical targets of our moral concern, such as pigs or chickens. More to the point, the idea that the experiences of some animals never rise above the palest hint of a feeling sits in tension with our best understanding of the evolutionary role of valenced experience. One of the most important functions of pains and pleasures is to encourage animals to pursue fitness-improving behaviors and to discourage animals from engaging in fitness-reducing behaviors. The felt goodness or badness of an action provides a motivational oomph that tells an animal how to behave. Under normal conditions, motivational force generally co-varies with the intensity of the felt goodness or badness. But by definition, extraordinarily mild experiences feel almost indistinguishable from neutral experiences. Subjective experiences so faint as to barely register would probably do a poor job motivating an animal.

Of course, this is a complicated issue, and there are replies to the above argument that are worth considering. It’s certainly possible that insects and crustaceans have characteristically less intense experiences than, say, pigs and chickens. Nonetheless, anyone who grants that insects and crustaceans are sentient but denies they merit attention on the grounds that their experiences are so faint owes us an evolutionary story about the connection between intensity and motivation.

Why Read the Whole Report?

If you read the report in full, you’ll discover the reasons I believe cognitive sophistication is a poor indicator of intensity range, why I’m excited about examining neural oscillations in nonhuman animals, and what questions I think are worth investigating further. And if you slog through the 123 footnotes, you’ll be rewarded with a smattering of interesting ideas, including the claim that humans may have the best orgasms (both male and female) in the animal kingdom and the claim that human childbirth may be so painful not because of our large heads (marmosets actually have greater head-to-pelvis disproportion) but because painful cries elicit assistance from other humans.

This area of research is admittedly quite speculative, and I regret that, due to a confluence of complexity, I was unable to provide a more quantitative accounting of my credences in various propositions. Nonetheless, if we’re serious about comparing interventions that target different species, we inevitably must confront difficult questions. I hope to have taken an initial step in helping map the terrain that we will have to traverse if we are ever to be confident that we are distributing resources across species efficiently.

Credits

This research is a project of Rethink Priorities. It was written by Jason Schukraft. Thanks to Michael Aird, Janique Behman, Kim Cuddington, Marcus Davis, and Derek Foster for helpful feedback on earlier drafts. If you like our work, please consider subscribing to our newsletter. You can see more of our work here.

Notes