The evolutionary origin of sentience is a foundational problem in biology. The object of analysis is defined (arguably without sufficient precision) as the organismal capacity to have subjective experiences with attractive or aversive qualities, such as pain and pleasure. While most sentience research is focused on animals, the growing literature on plants’ behaviour, cognition and putative sentience is an indication of the relevance of the question concerning the evolutionary origin of sentience. The same applies to bacteriological research on minimal cognition and putative sentience. Moreover, identifying sentience is fundamental for any ethics that has a sentientist foundation (i.e., whereby suffering grounds moral considerability). A noticeable trend stemming from animal research is that the growing phylogenetic and behavioural evidence is interpreted in terms of 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. Two general kinds of hypotheses clash at this juncture. The continuity hypothesis suggests that sentience is a primitive property of cellular life; the discontinuity hypothesis – which naturally comes in a variety of forms – suggests that sentience is an evolutionary innovation. This project aims to answer the following question: does contemporary biological research provide good reasons to cut phylogeny sharply between sentient and non-sentient organisms? The project aims to achieve two interrelated objectives.

1. Types of empirical evidence and theoretical considerations supporting specific hypotheses concerning the evolutionary origin of sentience:
We shall analyse how sentience ascription might be evidentially grounded in animal, plant and bacterial research. Our analysis shall focus on two kinds of biological evidence, phylogenetic and behavioural, stemming from a variety of biological sciences. Comparative phylogenetics aims to evaluate, through the identification of structural homologies and functional analogies, whether specific molecular, morphological, physiological and cognitive phenotypes are sentience indicators. Behavioural research aims to evaluate the degree of organismal flexibility in behaviour and whether the postulation of the “hedonic control of behaviour” (i.e., the ability on the part of the organism to use experiences with attractive or aversive qualities to guide behaviour) can be warranted. Both kinds of research are characterised by a series of specific challenges, particularly when applied to organisms of different lineages. Identifying and analysing the theoretical considerations (and putative biases) underlying the interpretation of these two kinds of evidence is one aim of the project. One general extrapolation based on a cursory look of the literature is that, while animal researchers oen postulate that the hedonic control of behaviour makes a difference to the animal by co- determining its behavioural choices, this interpretation is oen resisted when applied to organisms of other natural kingdoms and domains. At the extreme, molecular bacteriology assumes that organismal decision-making is accountable in terms of biochemistry: put crudely, it is proteins that determine bacterial decisions. This epistemological asymmetry requires careful philosophical analysis.

2. Philosophical implications of sentience research:
In molecular bacteriology, the machine analogy is assumed, with the ultimate implication that individuals’ behavioural variability and putative organismal choice are explained away in terms of molecular determination. Thus, what justifies the application of the hedonic control model or of the molecular determination model across phylogeny? Notably, the application of the molecular model of explanation to animal behaviour would dispense of organismal choice, sentience and free will. This perturbing prospect drives the epistemological part of the project, which will analyse the theoretical considerations (and putative biases) underlying the choice of a specific explanatory model in the behavioural sciences. In case sentience ascription is widened, bioethical implications ensue. If the moral community includes a large part of the biota, a sentientist perspective per se seems to preclude the privileging of the interests of one species and the exploitation of others. Henceforth, unless sentientism finds a way to satisfactorily answer the related questions of how to conceptualise and characterise with precision the degree of sentience sufficient for moral considerability, a new kind of foundation for organismal moral considerability would be needed. It is this incipient challenge to sentientist ethics that prompts the ethical part of the project.