Consciousness may have begun long before humans evolved

For centuries, consciousness has puzzled philosophers and scientists alike. What makes us aware? Where does the spark of experience come from? For many years, the answer seemed obvious. Awareness was tied to the brain’s most advanced feature, the cortex.

A recent review by Peter Coppola of the University of Cambridge paints a more ancient picture, suggesting that consciousness may arise from deeper, older brain structures.

Consciousness has ancient roots

Coppola examined research stretching back over a hundred years. He pulled insights from neuroimaging, stimulation studies, case reports, and animal experiments.

His findings suggest that the roots of awareness may extend back hundreds of millions of years. Instead of being uniquely human, consciousness may stem from neural machinery shared with reptiles and fish.

This idea broadens the scope of what we call experience. If consciousness extends beyond humans, it reshapes our understanding of animal life, intelligence, and even the ethical treatment of other species. It raises the question of whether awareness is rare – or widespread – in the natural world.

Shocking effects beneath the cortex

“The leading theories of consciousness suggest that the outer layer of the human brain, called the cortex, is fundamental to consciousness,” Coppola said. He compared the subcortex to electricity powering a television. Necessary, but not sufficient alone.

Stimulation experiments reveal striking differences. Altering cortical activity can shift self-perception or cause hallucinations. But stimulating subcortical areas brings dramatic changes.

“Changing the subcortex may have extreme effects. We can induce depression, wake a monkey from anesthesia or knock a mouse unconscious,” Coppola added. Even the cerebellum, once thought irrelevant, plays a role in shaping awareness.

Consciousness built on primal feelings

The subcortex regulates primal states like hunger, thirst, fear, and pleasure. These raw emotions, called “primary affects,” motivate behavior across species.

Coppola describes them as building blocks for more complex awareness. Consciousness, in this view, may begin as the simple feeling of what it is like to exist.

The cortex does not vanish from this picture. It layers language, planning, and memory onto the primal foundation. Coppola stresses that the cortex adds sophistication but may not be the origin of consciousness itself.

Clues from brain injuries

Coppola also turned to clinical evidence. Severe cortical damage often impairs awareness, but not always completely. In contrast, damage to subcortical structures frequently results in unconsciousness or death.

Some rare cases challenge assumptions. Children born with hydranencephaly lack much of the cortex, yet reports show they can play, recognize people, and enjoy music.

“According to medical textbooks, these individuals should be in a permanent vegetative state. However, there are reports that they can feel upset, play, recognize people, or show enjoyment of music,” noted Coppola.

Animal experiments echo this. Across mammals, removing the cortex does not erase behavior.

“Across mammals – from rats to cats to monkeys – surgically removing the neocortex leaves them still capable of an astonishing number of things. They can play, show emotions, groom themselves, parent their young, and even learn,” Coppola said.

Human and animal consciousness

The findings suggest that human consciousness may not be entirely distinct from other animals. If awareness springs from ancient brain structures, the difference between humans and animals may be smaller than once believed.

However, Coppola emphasized that our cortex enriched this foundation. Humans gained moral reasoning, creativity, language, and narrative selfhood. Still, the ancient subcortex may have provided the initial spark.

“Different authors have thought that such basic feelings were the first experiences to be engendered in the history of our world – and perhaps the ‘lowest level of consciousness,’” said Coppola.

Rethinking how we measure awareness

These insights hold profound meaning for medicine. Doctors often look at cortical activity when judging consciousness in brain-injured patients. Coppola’s work suggests that subcortical integrity may be equally vital.

This raises difficult ethical questions. If some patients retain subcortical function, they might possess rudimentary awareness overlooked by current methods.

This recognition could alter both treatment approaches and end-of-life decisions. It also emphasizes the need for improved diagnostic tools. Understanding how awareness arises could prevent misdiagnoses that profoundly affect patient care and family choices.

Coppola’s review urges a broader perspective. Rather than seeing consciousness as a recent achievement tied only to the cortex, it may be better understood as an ancient solution shaped by evolution. The cortex refines and expands it, but the spark may lie in older circuits that remain with us today.

The study is published in the journal Neuroscience & Biobehavioral Reviews.

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