Multiple groups of animals do fail certain, or even likely all, criteria. For example, sponges do not have neurons and therefore fail criteria 1 − 3. Although I’m not aware of tests of 4-8 in the sponges, it seems reasonable to suppose that the lack of a nervous system would also preclude endogenous neurotransmitter systems and many of the behavioral criteria.
Importantly, it is not just the number of criteria but also which criteria are fulfilled when considering the likelihood of pain or sentience. Some criteria provide more important evidence for sentience than others. In particular, criteria 2⁄3 and 5 have been considered important evidence by many philosophers and scientists. The roundworm, C. elegans, fails criterion 2 according to Irvine (2022); we can have reasonably high confidence that this failure is not due to an absence of evidence, but rather evidence of absence, given that we have a complete connectome of the C. elegans nervous system (302 neurons per animal). The fact that all adult insects fulfill criterion 2 with very high confidence, and that we find fulfilment of criterion 3 across the Holo/Hemimetabola split (suggesting the potential for broad taxonomic conservation of this criterion), is a meaningful distinction between these animal groups (at least to me, in the context of this framework).
Irvine E (2022) Independence, weight, and priority of evidence for sentience. Animal Sentience 32 (10). DOI: 10.51291/2377-7478.1724.
This comment is representative only of MRB’s opinions and expertise, and not the other post/publication authors.
Is there any animal that is found to fail these criteria?
Multiple groups of animals do fail certain, or even likely all, criteria. For example, sponges do not have neurons and therefore fail criteria 1 − 3. Although I’m not aware of tests of 4-8 in the sponges, it seems reasonable to suppose that the lack of a nervous system would also preclude endogenous neurotransmitter systems and many of the behavioral criteria.
Importantly, it is not just the number of criteria but also which criteria are fulfilled when considering the likelihood of pain or sentience. Some criteria provide more important evidence for sentience than others. In particular, criteria 2⁄3 and 5 have been considered important evidence by many philosophers and scientists. The roundworm, C. elegans, fails criterion 2 according to Irvine (2022); we can have reasonably high confidence that this failure is not due to an absence of evidence, but rather evidence of absence, given that we have a complete connectome of the C. elegans nervous system (302 neurons per animal). The fact that all adult insects fulfill criterion 2 with very high confidence, and that we find fulfilment of criterion 3 across the Holo/Hemimetabola split (suggesting the potential for broad taxonomic conservation of this criterion), is a meaningful distinction between these animal groups (at least to me, in the context of this framework).
Irvine E (2022) Independence, weight, and priority of evidence for sentience. Animal Sentience 32 (10). DOI: 10.51291/2377-7478.1724.
This comment is representative only of MRB’s opinions and expertise, and not the other post/publication authors.
(Not an animal scientist or a scientist of any nature btw!)
I’d guess sessile animals (e.g. mussels) fail (at least) motivational tradeoffs and analgesia preference.