Table Introduction

While invertebrates make up the majority of animal species, our knowledge about their capacity for valenced experience is overlooked compared to existing evidence about vertebrates. In particular, whether invertebrates have the capacity to have valenced experience is uncertain, and hence, it remains unclear whether these organisms have a welfare of their own we should care about.

Rethink Priorities has been systematically exploring this issue during the past months. First, we examined the philosophical difficulties inherent in the detection of instances of morally significant pain and pleasure in nonhumans. Second, given the current epistemic state about invertebrate consciousness, we have been compiling and analyzing relevant scientific evidence regarding this issue. In particular, we investigated the degree to which different features potentially indicative of phenomenal consciousness are found throughout different taxa. In a second post, we described our approach, the rationale of this project, and its limitations. The features we believe to be most relevant for assessing invertebrate sentience are explained in detail in a third, fourth, and fifth post.

In this sixth post, we present our summary of findings, both in narrative form and as a database.

Overview

The database is available here. It is an interactive table, where we summarize scientific data about 53 features potentially indicative of the capacity for valenced experience and examine the degree to which these features are found throughout 18 representative biological taxa. 12 invertebrate taxa are included: honey bees (genus Apis), cockroaches (genus Periplaneta), fruit flies (Drosophila melanogaster), ants (family Formicidae), spiders (order Araneae), the nematode Caenorhabditis elegans, sea hares (genus Aplysia), moon jellyfish (genus Aurelia), crabs (infraorder Brachyura), crayfish (family Cambaridae), and octopuses (family Octopodidae). For comparative purposes, we included three kinds of non-animal organisms –prokaryotes, protists and plants (kingdom Plantae)– and three vertebrate species –chickens (Gallus gallus domesticus), cows (Bos taurus), and humans (Homo Sapiens).

For each taxon and feature, we reviewed the existing literature and determined whether there was sufficient scientific data to make a call as to whether that taxon possesses the feature in question. Then, we evaluated the likelihood that the taxon possesses that feature. For those cases where we found direct evidence, we established four different responses corresponding to four rough probability ranges:

• “Likely No”: representing credences of 0% - 25%
• “Lean No”: 25% - 50%
• “Lean Yes”: 50% - 75%
• “Likely Yes”: 75% - 100%

As mentioned in a previous post, these four “credence buckets” represent our position regarding whether an animal possesses a feature; they do not necessarily represent the extent to which the animal possesses that feature. Given that current evidence about invertebrate consciousness is limited and unequal –i.e. some taxa have been much more studied than others, or specific features, unlike others, are well-studied phenomena– our credences are not necessarily well-calibrated in all cases. Further research is likely to contribute to revising and improving our confidence and reliability in our assessment of features potentially indicative of consciousness in different invertebrate taxa.

On top of that, there are several cases where no direct evidence of a specific feature for a given taxon was found. For those cases in which there have been only indirect studies and a specific feature was expected to be observed but, finally, no evidence arises, we used the category “not observed”. When no direct or indirect empirical evidence was found about a specific feature for a determined taxon, it was flagged as “unknown”. Additionally, a handful of features, such as average lifespan or brain neurons, are populated with short comments or numerical responses, as the case may be.

All the data compiled in the table is easily accessible: the taxa are presented in the columns and the features as rows. The consulted bibliography is linked to each cell, oftentimes with accompanying clarificatory quotes and/or commentary. In addition, our database offers a filter by taxon and attributes that enables users to filter and limit the data displayed within the table.

In addition to the information compiled in the database, an accompanying narrative report (part 1, part 2) summarizes our main findings about the extent to which the considered invertebrate taxa and other organisms display various features potentially indicative of consciousness.

Furthermore, we explored whether each feature can operate unconsciously in humans, since that might be a good defeater for that indicator or function when assessing consciousness in other non-human individuals. In this case, each feature was evaluated following the same procedure and nomenclature cited above. These findings are also compiled in the table, and they are further described in this narrative report.

We expect this work will enable animal welfare advocates to explore and consider relevant evidence about whether invertebrate individuals of a given species or taxon have the capacity for valenced experience. In forthcoming work, we discuss and analyze whether invertebrate welfare is a promising cause area and suggest possible next steps in this regard.

Credits

This essay is a project of Rethink Priorities.

It was written by Daniela R. Waldhorn with contributions from Jason Schukraft, Peter Hurford, and Marcus A. Davis. The database was developed by Daniela R. Waldhorn, Jason Schukraft, Max Carpendale, Peter Hurford, and Marcus A. Davis. Haven King-Nobles, Brandon Perry, Gavin Taylor, Kyle York, Tom Houlden, Ronke Bankole also contributed research. Table programming was engineered by Timothy “Manu” Meixell. Ashley Francis, Gabrielle Hass, Riley Peebles, and Avi Iyer helped with copyediting. Thanks to Kieran Greig and Luke Muelhauser for important feedback. Thanks to Catherine Low for help with project coordination.