Does a tree have awareness? Could a hermit crab or a slug feel anything at all? These questions sound like late-night musings better suited to philosophy class than scientific inquiry. However, according to a new paper from Michigan State University, they’re central to how we define and protect conscious life on Earth.
In Biology & Philosophy, MSU doctoral candidate Jonah Branding argues that modern science and ethics have become tangled in the question: how can we tell which creatures are conscious?
To help clarify decades of confusion, Branding has developed what he calls a “decision tree,” a conceptual map that connects competing ideas about consciousness and provides a way to navigate them logically.
“There has been a lot of work on the question of animal consciousness in recent years, and claims about consciousness are starting to be taken seriously for more and more organisms,” Branding said in a press release. “In the 1990s, there was serious debate over whether chimpanzees are conscious. Today, there is serious debate over whether plants are conscious.”
That shift, from primates to plants, reflects how dramatically the boundaries of consciousness have expanded in the past few decades. Yet, as Branding notes, these discussions often talk past each other.
His new framework aims to unify the field by tracing the roots of disagreement back to how researchers identify the so-called “markers” of consciousness: observable features such as complex behaviors, specialized brain structures, or sophisticated learning patterns.
If an organism shows enough of the right markers, scientists tend to assume it’s conscious. However, what about species that show few or none? Are they non-conscious, or are our tools simply too limited to tell? Branding calls this dilemma the “exclusion question,“ and it lies at the heart of his work.
In philosophical shorthand, there are two camps. The first, which Branding labels symmetry, assumes that if a being lacks the usual markers, it’s probably not conscious. The second, asymmetry, maintains that we can’t draw that conclusion because the absence of evidence isn’t evidence of absence.
“I argue that this disagreement partially reflects a deeper disagreement about how markers are identified,” Branding writes. “To this end, I point to three ‘paths’ from specific ideas about marker identification (namely, theory-based, analogy-based, and function-based approaches) to one or the other view on exclusion.”
To unpack those approaches, Branding looks at three primary ways scientists and philosophers have historically tried to identify consciousness: theory-based, analogy-based, and function-based. Each, he says, comes with its own strengths—and its own philosophical traps.
The theory-based approach starts with what we know best: human consciousness. Researchers use neurological and psychological theories derived from humans to decide which other creatures might also be conscious.
However, this strategy runs into what Branding calls the “Distribution Catch-22.” To form a general theory of consciousness, we need to know which animals are conscious. However, we can’t know which animals are conscious until we have a general theory. That circularity, he argues, makes the approach inherently limited.
Instead, the analogy-based method looks for similarities between humans and other species. If a fish or octopus behaves in ways that seem “mind-like,” perhaps that’s enough evidence of sentience.
However, here, too, bias creeps in. As Branding explains, human intuitions about what looks “conscious” may not apply universally. Our ability to recognize minds might have evolved to detect familiar, human-like patterns, social cues, facial expressions, or language, making us blind to forms of awareness that look nothing like our own.
The third path, function-based reasoning, links consciousness to what it does rather than what it looks like. In this view, consciousness serves an adaptive role: helping organisms integrate sensory information, make flexible decisions, and balance competing needs.
Animals that perform such complex, trade-off behaviors might therefore be conscious. As Branding points out, Hermit crabs can assess their environment and even abandon prized shells when shocked, suggesting that they could weigh discomfort against safety.
By contrast, simpler organisms that never exhibit such flexibility, for example, worms or certain crustaceans, might function more like biological machines. That logic appeals to scientists searching for testable definitions. However, it also risks drawing hard lines where none may exist, excluding forms of awareness we don’t yet understand.
What sets Branding’s paper apart is its approach. Rather than attempting to settle the debate, it maps it out. His ‘decision tree’ connects each method to either the symmetry or asymmetry view, demonstrating how one’s assumptions about biology and philosophy shape their conclusions. It’s not a definitive answer, but a diagnostic tool that helps us understand why we disagree in the first place.
Using Branding’s “decision tree,“ dolphins clearly fall on the conscious side of the spectrum. A theory-based approach links their large, complex brains to neural markers of awareness. An analogy-based view notes their empathy, self-recognition, and cultural learning, all human-like traits of mindedness. A function-based perspective highlights their flexible hunting, problem-solving, and social decision-making behaviors, which integrate information much like conscious thought. By every branch of Branding’s framework, dolphins meet the criteria for consciousness.
Conversely, going back to the headlining question: do trees think? According to Branding’s decision tree, the answer is probably not. Trees lack any nervous system or centralized information-processing structure that could support such experiences, failing the theory-based test. They also don’t display the flexible, goal-directed behaviors that would count as analogies to animal minds, disqualifying them under the analogy-based path. And while plants respond to light, gravity, and touch, these are automated physiological processes, not the function-based decision-making or sensory integration that consciousness requires. Branding’s model, in other words, places trees firmly outside the boundaries of awareness—they live, react, and adapt, but they do not feel.
Branding argues that misidentifying the boundary of awareness risks serious ethical errors—either underestimating the suffering of creatures that do feel, or overextending moral concern to those that don’t.
That has direct implications for everything from animal welfare laws to environmental policy. Recognizing sentience in octopuses and crabs has already influenced legislation in the United Kingdom. If future research supports even the possibility of plant or fungal awareness, the ethical terrain could expand dramatically, challenging how humans value the living world.
Branding’s “map“ serves as both a philosophical compass and a call for humility. In one notable example, he revisits a centuries-old debate, quoting Tibetan philosopher Gendun Chopel in his paper, who mocked early claims of plant sentience by asking whether leather shrinks near a fire because it “feels heat.“ Branding uses this ancient exchange to highlight how long humans have wrestled with the same question: where does consciousness end?
“These are questions of how we interact with the world,“ Branding said. “There are major ethical implications about who we have to care about morally.”
Ultimately, the study suggests that our understanding of consciousness may always be partial, shaped as much by our own cognitive limits as by the creatures we study. Nevertheless, having a philosophical roadmap may help future researchers navigate this uncertain terrain with sharper tools, deeper empathy, and more wonder.
“Consciousness science is notorious for its twists and turns,“ Professor of Philosophy at City University of New York and York Research Chair in Animal Minds, Dr. Kristin Andrews, explained. “In his paper, Branding offers a road map to help us answer some of the most difficult questions about which beings are conscious.”
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com