I suspect that there exists a belief that below a certain threshold there is no consciousness or capacity for welfare—a discontinuity—and thus animals such as nematodes are out of scope.
Note many people rule out animals way more cognitively sophisticated than nematodes postulating such a discontinuity. Bryan Caplan said the graph below “nicely summarizes my [Bryan’s] broader view”.
I would not be surprised if the absolute value of the welfare per animal-year decreased much faster than exponentially with the number of neurons for a sufficiently low number of neurons. However, I assume an exponential decrease up to the number of neurons of nematodes given the large uncertainty about whether there is such a transition, and the number of neurons for which it would happen. I believe there should be some models according to which the welfare per animal-year does not abruptly go to 0, and the expected welfare per animal-year will be determine by such models.
Given the determinate development of their nervous systems, 30-some years ago it was taken as given that C. elegans are too simple to learn. However, once researchers turned to examine learning and memory in these tiny animals, they found an incredible amount of flexible behavior and sensitivity to experience. C. elegans have short-term and long-term memory, they can learn through habituation (Rankin et al., 1990), association (Wen et al., 1997), and imprinting (Remy & Hobert, 2005). They pass associative learning tasks using a variety of sensory modalities, including taste, smell, sensitivity to temperature, and sensitivity to oxygen (Ardiel & Rankin, 2010). They also integrate information from different sensory modalities, and respond differently to different levels of intoxicating substances, “support[ing] the view that worms can associate a physiological state with a specific experience” (Rankin, 2004, p. R618). There is also behavioral evidence that C. elegans engage in motivational trade-offs. These worms will flexibly choose to head through a noxious environment to gain access to a nutritious substance when hungry enough (Ghosh et al., 2016)—though Birch and colleagues are not convinced this behavior satisfies the marker of motivational trade-offs because it appears that one reflex is merely inhibiting another (Birch et al., 2021, p. 31).
C. elegans are a model organism for the study of nociceptors, and much of what we now know about the mechanisms of nociception comes from studies on this species (Smith & Lewin, 2009). Behavioral responses to noxious stimuli are modulated by opiates, as demonstrated by a study finding that administration of morphine has a dose-dependent effect on the latency of response to heat (Pryor et al., 2007). And, perhaps surprisingly, when the nerve ring that comprises the C. elegans brain was recently mapped, researchers found that different regions of the brain support different circuits that route sensory information to another location where they are integrated, leading to action (Brittin et al., 2021).
Even if we grant the author’s low confidence in nematodes’ having marker five (motivational trade-offs), current science provides ample confidence that nematodes have markers one (nociceptors), two (integrated brain regions), four (responsiveness to analgesics), and seven (sophisticated associative learning). Given high confidence that nematodes have even three of these markers, the report’s methodology [Birch et al. (2021)] would have us conclude that there is “substantial evidence” of sentience in nematodes.
Furthermore, the welfare of soil animals would still dominate even if all animals with fewer neurons than shrimps, which are the ones with the least neurons covered in Bob’s book, had a welfare per animal-year of exactly 0. This would imply a total welfare of exactly 0 for farmed BSF larvae and mealworms, and soil springtails, mites, and nematodes. Yet, soil ants and termites would still be considered. I calculate they have 2.91 and 1.16 times as many neurons as shrimps. Below is a graph comparing the welfare of soil ants and termites with that of other animal populations. I have not set the welfare of farmed BSF and mealworms to 0, but doing this would only slightly reinforce my point.
To clarify: I think soil animals should be an area of focus. I’m unconvinced on nematodes specifically—but I think there’s good arguments for assessment of the life experiences of higher-neuron soil species being a very important thing.
Thanks for clarifying, Kestrel. I would be curious to know what makes you unconvinced about nematodes in light of Andrews (2024) and Becerra at al. (2023).
Thanks, Kestrel.
Note many people rule out animals way more cognitively sophisticated than nematodes postulating such a discontinuity. Bryan Caplan said the graph below “nicely summarizes my [Bryan’s] broader view”.
I would not be surprised if the absolute value of the welfare per animal-year decreased much faster than exponentially with the number of neurons for a sufficiently low number of neurons. However, I assume an exponential decrease up to the number of neurons of nematodes given the large uncertainty about whether there is such a transition, and the number of neurons for which it would happen. I believe there should be some models according to which the welfare per animal-year does not abruptly go to 0, and the expected welfare per animal-year will be determine by such models.
I would say they have at least a 10 % chance of being sentient. From the article “All animals are conscious”: Shifting the null hypothesis in consciousness science by Kristin Andrews (here is a crosspost of Faunalytics’ summary of it):
Furthermore, the welfare of soil animals would still dominate even if all animals with fewer neurons than shrimps, which are the ones with the least neurons covered in Bob’s book, had a welfare per animal-year of exactly 0. This would imply a total welfare of exactly 0 for farmed BSF larvae and mealworms, and soil springtails, mites, and nematodes. Yet, soil ants and termites would still be considered. I calculate they have 2.91 and 1.16 times as many neurons as shrimps. Below is a graph comparing the welfare of soil ants and termites with that of other animal populations. I have not set the welfare of farmed BSF and mealworms to 0, but doing this would only slightly reinforce my point.
To clarify: I think soil animals should be an area of focus. I’m unconvinced on nematodes specifically—but I think there’s good arguments for assessment of the life experiences of higher-neuron soil species being a very important thing.
Thanks for clarifying, Kestrel. I would be curious to know what makes you unconvinced about nematodes in light of Andrews (2024) and Becerra at al. (2023).