In From Signal to Symbol (2021, p. x) Ron Planer and Kim Sterelny argue that any “adequate” theory of language evolution “must identify a plausible trajectory from great-apelike communicative abilities to those of modern humans where each step along the way is small, cumulative and adaptive (or at least not maladaptive: there might be some role for drift)”. They are not alone in invoking such a constraint. Gradualism is cited as an important assumption amongst those concerned with the evolution of cognition and the nature of animal minds going back to Darwin’s mental continuity thesis (Darwin 1871 [2013]). Gradualism is often invoked by scholars in pushing back against the anthropocentric allure of human uniqueness, the idea being that the postulation of the evolution of entirely novel cognitive capacities in our lineage alone is evolutionarily implausible. Indeed, Planer and Sterelny call the capacities such theories postulate “miracles” (p. 213). In this paper, I explore the evolutionary justification for such claims in comparative and evolutionary psychology in light of work on gradualism in evolutionary developmental biology (evo-devo). I ask, are evolutionary trajectories made up of “small, cumulative and adaptive” steps indeed more evolutionarily plausible than those that postulate entirely novel cognitive capacities within lineages? If so, why? One reason one might question the gradualist assumption (or at least suggest it needs to be applied with more care) comes from evidence that, although change at the genetic level is typically gradual, gradual genetic evolution is not always associated with gradual phenotypic evolution (Moczek 2008). As understanding of the relationship between genes and phenotypes in development has grown, so too has an appreciation of the important role played by neutral evolution and other processes in the evolution. At least from the perspective of evo-devo, these developmental processes undermine any bald gradualist assumption based in the gradualism of micro-evolution — even if genetic evolution is gradual, one cannot assume that phenotypic evolution will be. Another justification for gradualism lies in the randomness of variation. It is much more likely for large random phenotypic changes to be deleterious than small ones. Given this, we expect that most large phenotypic shifts will fail to persist and propagate in populations (Calcott 2011). Again, here, work in evo-devo on plasticity and other mechanisms of adaptation suggests that there are ways that developmental systems have evolved to make large adaptive shifts in phenotype possible (Moczek 2008) and undermines any bald gradualist assumption. This article explores these and other justifications for a gradualist assumption in comparative and evolutionary psychology. Ultimately, I offer a novel account of gradualism as a constraint on theorising in comparative and evolutionary psychology which better reflects contemporary evolutionary developmental biology. References Calcott, B. 2011. Wimsatt and the Robustness Family: Review of Wimsatt’s Re-engineering Philosophy for Limited Beings. Biology and Philosophy. 26:281-293. https://doi.org/10.1007/s10539-010-9202-x Darwin, C. 1871. The Descent of Man and Selection in Relation to Sex. Wordsworth Editions Limited (2013), Hertfordshire, UK. Moczek, A. P. 2008. On the Origins of Novelty in Development and Evolution. BioEssays. 30:432-447. https://doi.org/10.1002/bies.20754 Planer, R. J. and Sterelny, K. 2021. From Signal to Symbol: The Evolution of Language. The MIT Press.

The scientific status of folk psychology (FP) is a topic of ongoing debate (Hochstein 2017). One common criticism of the use of FP in the sciences is that FP accounts produce feelings of understanding when in fact they are poor guides to truth. For example, in the context of comparative psychology, Papineau and Heyes (2006) observe that it is “easy, perhaps irresistible” to interpret some experimental results in terms of FP (p. 188). Penn (2011) agrees, writing “there is no doubt, of course, that folk psychological explanations are ‘simpler for us’ to understand” (p. 259); however, “the job of comparative cognitive psychology was supposed to be to open up the black box of animal minds to functional and algorithmic specification—not simply reiterate the kinds of explanations the ‘folk’ use” (p. 259). Following Carl Hempel, many philosophers of science would agree that subjective feelings of understanding are poor guides to good explanation. According to this view, such feelings are at best epistemically irrelevant and at worse misleading (Trout 2002). Combined with the idea that FP is no more than a collection of platitudes about mental states and behaviour, the situation appears deeply problematic: platitudes lead to feelings of understanding, but such feelings are doing little more than tracking our common-sense knowledge, rather than providing insights into the workings of the mind. However, there are alternative ways of characterising both FP and the role of understanding in the sciences. First, FP has been described as a model, rather than a collection of platitudes (Godfrey-Smith 2005). Second, some argue that understanding is necessary for explanation (De Regt 2017). Under this latter view, understanding is not a mere ‘aha’ feeling but rather concerns the skills and judgments scientists employ when constructing explanations (what De Regt calls “pragmatic understanding”). Moreover, to explain a phenomenon is to fit it into a theoretical framework and models are crucial mediators in this process. Applying these ideas, we can construct an alternative account of FP: it facilitates pragmatic understanding in the construction of explanations in psychology. In this paper, I advance and defend this account of the role of folk psychology in scientific practice. References De Regt, H.W. 2017. Understanding Scientific Understanding. Oxford University Press. Godfrey-Smith, P. 2005. Folk Psychology as a Model. Philosophers’ Imprint. 5(6):1-16. Hochstein, E. 2017. When does ‘Folk Psychology’ Count as Folk Psychological? The British Journal for the Philosophy of Science. 68(4):1125-1147. Papineau, D., and Heyes, C. 2006. Rational or Associative? Imitation in Japanese Quail. In S. Hurley & M. Nudds (eds.), Rational Animals? Oxford University Press, pp. 187-195. Penn, D. 2011. How Folk Psychology Ruined Comparative Psychology: And How Scrub Jays Can Save It. In R. Menzel and J. Fischer (eds.), Animal Thinking: Contemporary Issues in Comparative Cognition. MIT Press, pp. 253-266. Trout, J. D. 2002. Scientific Explanation and The Sense of Understanding. Philosophy of Science. 69(2):212-233.

Morgan’s original canon (1894) was intended as a prophylactic against an anthropomorphic bias that he thought stemmed from the double inductive method, which explains seemingly identical behavior in animals and humans in terms of the same underlying causes. However, his defense of the method of variation, which introduces a bias of its own towards type-2 errors (Sober 2005), as well as the original canon’s reliance on vague terms like ‘higher’ and ‘lower’ psychical faculties, has been repeatedly reinterpreted and contested throughout the history of comparative psychology (e.g., Karin-D’Arcy 2005; Allen-Hermanson 2005; Meketa 2014; Heyes 2012; Fitzpatrick 2008). Despite these perennial disputes, Morgan’s canon has played a preeminent role in the methodology of comparative psychology, even if it is unclear what it precisely means or how exactly it should be used to direct research. This has frequently led to uncritical invocations of the canon to settle the task of theory selection when it is unsuited to do so. This talk is directed at ameliorating some systematic problems that pervades comparative psychology's use of the canon. I do this by developing a quantitative parsimony interpretation of Morgan’s canon, while simultaneously laying out the conditions for interpreting the evidential strength of individual invocations and showing how they can be evaluated against one another. On this interpretation, a theory or model is more parsimonious than another, if the fact that there is less of a local relevant feature gives us reason to prefer it. A theory or model establishes its relevant simplicity against a context to which it is bound, where being bound to a context implies being committed to counting in a certain way (Sober 1994). This implies that are multiple ways in which being simple in a certain way is relevant both within and across contexts (Okasha 2011, Kuhn 1962). For example, as Dacey (2016) highlights, the target of parsimony claims and invocations of Morgan’s canon include processes, energetic demands, structures, and inputs. Given that such claims are local and multiple, I offer a way of evaluating incompatible claims based on their justificatory strength and their degree of underdetermination. Doing so offers a principled way to direct further research that can account for both empirical as well as extra-empirical concerns. On this interpretation, the original spirit of Morgan’s canon can be preserved in so far as invocation of it employs a more fine-grained interpretation of both the purported simplicity claim underlying it and the demands of the mental continuity thesis that gave rise to it. Moreover, this interpretation foregoes the pitfalls of so-called ‘default’ reasoning that are pervasive in the discipline, while addressing the problems of both anthropomorphism, anthropodenialism, as well as uncritical invocations of the mental continuity thesis. References Allen-Hermanson, S. .2005. Morgan’s Canon Revisited. Philosophy of Science. 72(4):608-631. Dacey, M. 2016. The Varieties of Parsimony in Psychology. Mind & Language. 31(4):414-437. Fitzpatrick, S. 2008. Doing Away with Morgan’s Canon. Mind & Language. 23(2):224-246. Karin-D’Arcy, M. 2005. The Modern Role of Morgan’s Canon in Comparative Psychology. International Journal of Comparative Psychology. 18(3). Kuhn, T. S. [1962] 2012. The Structure of Scientific Revolutions: 50th Anniversary Edition. University of Chicago Press, Chicago, Il. Heyes, C. 2012. New Thinking: The Evolution of Human Cognition. Philosophical Transactions of the Royal Society B: Biological Sciences. 367(1599):2091-2096. Lloyd Morgan, C. 1894. An Introduction to Comparative Psychology. The Walter Scott Publishing Co, Ltd. London and Newcastle-on-Tyne. Meketa, I. 2014. A Critique of the Principle of Cognitive Simplicity in Comparative Cognition. Biology and Philosophy. 29(5):731-745. Okasha, S. 2011. Theory Choice and Social Choice: Kuhn versus Arrow. Mind. 120(477):83- 115. Sober, E. 1994. From a Biological Point of View: Essays in Evolutionary Philosophy. Cambridge University Press, Cambridge, UK. Sober, E. (2005). Comparative Psychology meets Evolutionary Biology. In L. Datson and G. Mitman (eds.), Thinking with Animals: New Perspectives on Anthropomorphism. Columbia University Press, New York, NY, pp. 85-99.

The mental continuity thesis is an assumption shared by many philosophers and scientists who study mind in nature. It states that the difference in mind between different creatures is one of degree not kind. It is an attractive thesis, as it can serve as a basis for the application of evolutionary reasoning in studying other minds. The mental continuity thesis, however, is by no means self-evident. If it is to figure as a premise that warrants evolutionary approaches in the study of other minds, it needs to be substantiated. What reasons do we have for accepting that minds exist on a continuum? What are the relevant entities that secures the difference in degree and not kind? An uncritical admission of the mental continuity thesis has historically led to unfounded anthropomorphism (e.g., anecdotal cognitivism). Morgan’s canon, a methodological principle whose intention is to ward against such anthropomorphism, states that explanations of animal behaviors should never invoke complex cognitive processes or mechanisms unless there is compelling independent evidence for doing so. Morgan’s canon thus seems to have an uneasy relationship with the mental continuity thesis. As Morgan’s canon urges us to avoid invoking human-based complex cognitive processes in our explanations of behavior in non-human organisms, how are we to reconcile this with the view that the only difference between the human mind and that of other creatures is one of degree not kind? In other words, what counts as compelling evidence for invoking “human-like” cognitive process that highlight a difference in degree and not kind in our explanations of non-human behavior? We suggest that the concept of homology may be a way to justify the use of seemingly anthropomorphic language and explanation in conceptualizing non-human minds and behavior. However, the scope of this justification is limited. Homology can only play a role of justifying the mental continuity thesis within a restricted taxonomic scope. Specifically, we argue that there is a “goldilocks” zone in which homologies can be optimally used in the role of justifying claims concerning mental continuity across species.