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 vertebrate animals, the growing literature on other lineages (ranging from invertebrates to plants) is an indication of the relevance of the question concerning the evolutionary origin of sentience. The same applies to 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. 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 and functional homologies and 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 subjective 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.

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. The analysis of animal behaviour instead might be grounded on the postulation of some form of agency and organismal choice: in this case, animal behaviour would be co-determined by subjective experiences with attractive or aversive qualities. What justifies the application of the hedonic control model or of the molecular determination model across phylogeny? Arguably, the application of the molecular model of explanation to animal behaviour would dispense of agency, organismal choice and sentience. The project aims to 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.

Project duration 18 month

Starting date 1st March 2023

This project is funded by the Fundação para a Ciência e a Tecnologia (FCT) through the funding Pex 2022.05256.PTDC.
DOI 10.54499/2022.05256.PTDC (