The evolutionary origin of sentience is a foundational problem in biology. A noticeable trend stemming from animal research is towards widening sentience ascription (as shown by the protection granted to some invertebrate species in some legislative frameworks). This interpretive change is rooted in the Darwinian theory of common descent. However, evolutionism by itself is silent on the question of the origin and phylogenetic distribution of sentience. The question I aim to explore is: does contemporary biological research provide good reasons to cut phylogeny sharply between sentient and non-sentient organisms? My analysis shall focus on two kinds of biological evidence, phylogenetic and behavioural.

In the first part of the talk I consider phylogenetic evidence. The fundamental problem of comparative phylogenetics is that the evidence uncovered might be merely analogical. The phylogenetic evidence can be considered as such only if, first, the presence in a reference organism of a particular phenotype is unproblematically associated with sentience and, secondly, if the target organism of a different lineage has a structurally homologous or functionally analogous trait. The former condition depends on the putative association of the reference trait with sentience (problematic because evolution might have produced different molecular, morphological, physiological and cognitive substrates for sentience). The second depends on the homology and analogy criteria used. Evidence of structural homology or functional analogy might thus be biased, affecting the way in which phylogenetic evidence is deployed to support sentience ascription.

In the second part of the talk I turn to consider behavioural evidence. From what I understand, behavioural analysis is generally couched in terms of ascertaining whether the organism exhibits significant degrees of behavioural flexibility, a notion frequently contrasted with automaticity or purely mechanical behaviour. However, the vernacular notion of automaticity is imprecise, potentially biasing the interpretation of the behavioural evidence supporting sentience ascription. In order to make the notion of flexibility more precise, I shall also make reference to the foundational literature in molecular bacteriology started in the 50s, which showed that bacterial responses exhibit various degree of behavioural flexibility. However, rather than being considered as an indicator of sentience, this behavioural flexibility was explained away; basically, organismal “decision-making” is accountable in terms of biochemistry: put crudely, it is proteins that determine bacterial decisions.

One general extrapolation based on a cursory look of the huge sentience research literature – encompassing animal and plant biology as well as bacteriology – is that, while animal researchers often postulate sentience, this interpretation is often resisted when applied to organisms of other natural kingdoms and domains. This epistemological asymmetry requires careful philosophical analysis, as it seems to be founded on applying two different explanatory models for reasons that I’m so far unable to fully grasp. The talks will make reference to several hypotheses concerning the phylogenetic distribution of sentience.