Source: Hayana Fernanda/Pexels.

Comparing animal welfare across species is fraught with conceptual and empirical challenges.¹ However, we know some progress has been made as we’ve learned how to identify the large differences in the emotional lives of individuals of the same species.

When trying to scale animal welfare across species, questions such as these arise: Can humans suffer more than other animals? Are our pains worse? And if they are, then how much worse are they? Is the most intense pain for a human ten times as bad as the most intense pain for a chicken? One thousand times as bad? More awful still? These are the puzzles that Bob Fischer and his team tackle in Weighing Animal Welfare: Comparing Well-being Across Species, which was just published open access by Oxford University Press. It’s freely available here.

To accomplish this daunting task of scaling welfare, Fischer, a senior researcher at Rethink Priorities and professor at Texas State University, assembled a diverse team to work on these questions about pain intensity across the animal kingdom. The contributors included comparative cognition experts, animal welfare scientists, neuroscientists, and philosophers. Together, they developed a method that let them outline some tentative answers.

Marc Bekoff: What are the major results of your research?

Bob Fischer: The upshot of Weighing Animal Welfare is that while there probably are differences between humans and other animals, they aren’t enormous differences. We estimate, for instance, that a pig’s pain can be roughly half as intense as a human’s, and a chicken’s a bit less. Put differently, we think that the best evidence supports the view that animals’ experiential peaks and valleys are relatively similar, varying based on their cognitive capacities.

Source: Oxford University Press/with permission.

If we’re in the ballpark of the truth, then that means pigs and chickens can suffer a lot! Imagine, if you can, suffering that’s half as intense as the worst suffering you’ve ever experienced. That would still be an awful experience. So, if we have good reason to prevent that kind of suffering in humans, then we have good reason to prevent it in these animals.

MB: How did you generate these estimates?

BF: There is no direct way to measure the intensities of pains across species. There is no neurological metric that makes the process straightforward. Likewise, many indirect methods aren’t helpful. For instance, we can’t use behavioral evidence, such as how hard animals will work to avoid pain. All animals do everything they can to avoid the worst experiences, so all we would learn from that method is how to compare pains within species. So, we had to get creative.

Our strategy involved looking at the many functions of states that feel good and bad to animals—scientists call them “valenced states.” Valenced states do lots of things for animals: they carry information about threats and opportunities, they help animals learn, they motivate action, and they help animals make tradeoffs. By comparing how well animals can perform these functions—that is, how much information they can represent, how much and how well animals can learn, etc.—we can begin to understand the possible differences in their valenced states. You can see some of the traits that we considered in Figure 1.

Traits that are relevant to the functions of six animals’ valenced states: pigs, chickens, salmon, octopuses, shrimp, and flies.

Source: Bob Fischer/with permission.

Once we had a picture of animals’ capacities, we built a model to aggregate this information into a single “welfare range” estimate per species, which is a way of representing how intense their experiences can be.

Of course, there were lots of complexities along the way. And if it weren’t so important to compare pain across species, this project might not be worth pursuing. But people make tradeoffs involving animals all the time that are, at least in part, based on assumptions about what animals feel. So, it’s important to try to compare the intensities of animals’ pains.

MB: Did you just study pain?

BF: No, we considered animals’ capacities for both positive and negative experiences. However, because pain is easier to study than positive experiences, many of the studies that we reviewed were focused on pain. And while the negative focus is unfortunate, pain is a useful test case, since it’s probably one of the most intense negative experiences that animals can have (compared to, say, boredom or anxiety, which are both negative but typically not as acute as intense pain). In addition, insofar as we think that it’s especially important to alleviate pain from a moral point of view, it’s good to spend a lot of time thinking about pain specifically.

MB: What do you hope your work accomplishes?

BF: We’re trying to make two main contributions. The first is to start a conversation about how best to make these comparisons. We know we haven’t offered the last word—or anything near it! However, research has to begin somewhere. By taking a first crack at this project, we’re hoping that others will point out the limitations of what we’ve done, suggest ways to do better, and then carry the work forward themselves. We would love to see a thriving field of research that considers whether and when there’s more at stake for a chicken than a pig—or a human.

The second contribution is to provide some first-pass, proof-of-concept results. People might have thought that, if anyone ever tried to quantify the differences in pain intensity across animals, the research would show that we can all but ignore the negative experiences of some animals, like invertebrates. On this view, if shrimp feel anything at all, it barely registers on the scale. But our work suggests otherwise. Yes, there probably are differences between species. However, we don’t think the evidence supports the view that the pain that those animals experience is completely trivial. We should treat those animals in a way that’s sensitive to their capacities.