Philosophers and scientists have long grappled with the profound question of consciousness—what it truly means for a living being to possess subjective experience and awareness. Traditionally, debates on animal consciousness have revolved around mammals with complex nervous systems, but recent discussions have expanded this inquiry to include smaller creatures and even plants. The implications extend far beyond theoretical musing; establishing which organisms experience consciousness shapes crucial ethical considerations, including animal welfare legislation and conservation priorities.
In a groundbreaking contribution to this evolving discourse, Jonah Branding, a philosophy PhD candidate at Michigan State University, has introduced a novel framework aimed at bringing clarity to the challenging task of determining consciousness across the biological spectrum. Published in the recent edition of the journal Biology & Philosophy, Branding’s work presents a decision tree—an analytical tool that offers a structured method to interrogate the presence of consciousness based on observable markers. This approach could influence how science and ethics approach questions as diverse as whether a hooked fish feels pain or whether more modest beings like ants and banana slugs have any internal mental states or simply respond reflexively to stimuli.
Consciousness science has been described as “notorious for its twists and turns,” a sentiment echoed by Kristin Andrews, a philosophy professor at the City University of New York and one of the original signatories of the 2024 New York Declaration on Animal Consciousness. Branding’s decision tree serves as a roadmap to navigate the myriad scientific, ethical, and philosophical issues intertwined with this inquiry. His framework critically examines the markers that are often assumed to correlate with consciousness, such as brain structures, behavioral complexity, and cognitive sophistication.
Markers, in this context, refer to measurable traits or behaviors thought to indicate the likelihood of mental experience. By cataloging and assessing these markers, Branding’s approach offers a systematic way to evaluate creatures that lie on different points of the consciousness spectrum. This has particular importance for less-studied organisms where evidence is scant or ambiguous, especially as interest in plant and invertebrate consciousness gains scientific traction.
Branding identifies a critical division in the debate: those who adopt what he terms the symmetry position versus the asymmetry position. Symmetry adherents demand sufficient positive evidence—an adequate number of consciousness markers—to attribute conscious experience to an organism. If the evidence is lacking, then the conclusion is that the organism is likely non-conscious. On the other hand, the asymmetry camp accepts that while the presence of markers strongly suggests consciousness, their absence does not conclusively indicate the absence of consciousness. This philosophical distinction underlies many disagreements about the consciousness of simpler organisms.
Delving deeper, Branding investigates the philosophical and empirical import of missing markers. He challenges researchers to interrogate why some markers hold significant weight and what their absence truly signifies in terms of first-person perspective and experience. This rigorous approach aims to refine and possibly reconcile conflicting methodologies for assessing consciousness, prioritizing transparency and consistency.
An illustrative example Branding highlights is the hermit crab. Despite lacking many classical markers—such as advanced brains or elaborate cognitive behaviors—hermit crabs exhibit intriguing intelligence. Their ability to select and switch shells in response to environmental challenges suggests a level of problem-solving and spatial navigation that complicates simplistic classifications. This example epitomizes the tensions in current consciousness research: how do we weigh observable behavior against the absence of more traditional neural structures?
Branding’s decision tree ultimately seeks to guide not only scientific inquiry but ethical action. By clarifying when it is justified to exclude an organism from considerations of consciousness, the framework helps define moral responsibilities toward different species. It addresses how humans should prioritize care and protection—a matter not only of academic debate but of real-world consequence in fields such as conservation and animal rights.
As the boundaries of consciousness research expand to encompass diverse life forms, frameworks like Branding’s become indispensable tools. They promote careful and systematic evaluation rather than guesswork, helping society make more informed decisions grounded in philosophy and empirical observation. Scholars, ethicists, and policy-makers can use this approach as a stepping stone toward a more inclusive understanding of mental experience across the natural world.
The ethical stakes of this discourse cannot be understated. Assigning or denying consciousness influences which beings are included within moral consideration—the spectrum ranging from complex mammals to simpler invertebrates, and now possibly to plants. If organisms traditionally ignored in these debates possess consciousness or something analogous, human interactions with ecosystems and nonhuman life must fundamentally change.
Branding’s work arrives at a pivotal moment in scientific philosophy, where advancing knowledge invites urgent reflection about the nature of experience itself. The decision tree acts as a fulcrum for ongoing research, encouraging a balance of skepticism and openness. Future studies spanning neuroscience, ethology, and philosophy will likely draw upon this tool to refine our understanding of the sentient landscape.
In sum, the exploration of consciousness is moving from abstract theorizing to structured frameworks that better inform both science and ethics. Jonah Branding’s marker-based decision tree stands as a significant advancement in delineating which organisms might be conscious and under what conditions we can reasonably exclude this attribution. This work is essential for fostering a nuanced, careful dialogue about awareness that respects complexity and uncertainty alike.
Subject of Research: Philosophy and science of animal and plant consciousness; ethical and scientific frameworks for and against attributing consciousness based on observable markers.
Article Title: Can a marker approach exclude?
News Publication Date: October 8, 2025
Web References:
http://dx.doi.org/10.1007/s10539-025-09989-x
Image Credits: Sue Nichols, Michigan State University
Keywords: consciousness, animal minds, philosophy of mind, cognitive ethology, consciousness markers, ethical implications, decision tree, animal welfare, cognition, sentience, comparative cognition, plant consciousness
