Probably not, according to Eric Schwitzgebel, a distinguished professor of philosophy at the University of California, Riverside.

In a new working paper, Schwitzgebel and Jeremy Pober, a former UCR graduate student who is now a postdoctoral researcher at the University of Lisbon, argue that conscious beings may be possible even if they are built from materials very different from those found in life on Earth. One example comes from the recent blockbuster "Project Hail Mary," which features a five-limbed alien with a rock-like exterior.

Rather than trying to define consciousness itself, the researchers begin with the assumption that consciousness is a real and recognizable phenomenon. Their focus is on a narrower question: Does consciousness have to depend on Earth-style biology?

The paper arrives at a time when debates about conscious artificial intelligence are becoming increasingly common. While the authors briefly address AI, they do not take a shared position on whether current systems are conscious. In fact, they disagree with each other on some aspects of the issue. Still, their broader argument leaves open the possibility that consciousness could one day emerge in AI, even if today's systems do not possess it.

The Idea of "Substrate Flexibility"

A central concept in the paper is what philosophers call "substrate flexibility."

The idea is simple. Some properties can exist in many different materials. A cup, for example, can be made from glass, plastic, metal, or other substances. A book can exist as printed pages or as a digital file. Likewise, records can be stored on vinyl or compact discs.

Schwitzgebel and Pober argue that consciousness belongs in this category as well.

In their view, consciousness is not necessarily tied to any single physical substance.

"The universe may contain minds stranger than we can imagine," Schwitzgebel said.

Alien Life May Take Many Forms

Astronomers estimate that the observable universe contains roughly 1 trillion galaxies. Planets appear to be abundant, and most likely have environments that differ dramatically from Earth's.

For their argument, Schwitzgebel and Pober estimate that at least 1,000 behaviorally sophisticated extraterrestrial civilizations have existed somewhere in the universe. They describe this figure as conservative and point to research suggesting that the median scientific estimate is greater than one civilization per galaxy at some point during a galaxy's lifetime.

Meanwhile, astrobiologists have explored the possibility that life elsewhere could be built from different materials than life on Earth. Researchers have considered alternative amino acids, alternative solvents, and even entirely different chemical structures.

Andy Weir's novel "Project Hail Mary" offers a vivid fictional example. In the book, readers encounter an alien species with a shell made of oxidized minerals, mercury blood, two circulatory systems, steam-powered muscles, and a crystal brain. The creature comes from an extremely hot world with an atmosphere saturated with ammonia.

The philosophers are not claiming that such exotic life definitely exists. Instead, they argue that if life can emerge under a wide range of chemical conditions, and if the universe provides countless opportunities for life to develop, it would be surprising if every successful evolutionary pathway arrived at the exact same biological ingredients.

Earth itself offers evidence of nature's creativity. Octopuses, bees, and dogs all process information differently. Even on our own planet, evolution has produced a wide variety of nervous systems rather than a single blueprint. According to the authors, the rest of the universe may display even greater diversity.

The Copernican Principle of Consciousness

The authors' main argument draws inspiration from the Copernican tradition in astronomy.

Over time, discoveries associated with Nicolaus Copernicus and later astronomers revealed that Earth is not the center of the solar system, the solar system is not the center of the galaxy, and the Milky Way is not the center of the universe. Humanity has repeatedly learned that its place in the cosmos is less special than once believed.

Schwitzgebel and Pober suggest that consciousness may deserve the same treatment.

If many behaviorally sophisticated species exist throughout the universe and possess very different biological structures, then assuming that consciousness belongs only to organisms like us would reflect what the authors call "terrocentrism" -- unjustified treatment of Earth life as uniquely privileged. They refer to this broader idea as the "Copernican principle of consciousness."

The researchers are not arguing that every advanced species must be conscious. Instead, they contend that if consciousness occurs among behaviorally sophisticated beings, it would be odd to conclude that only organisms with biology resembling ours could experience it.

History has repeatedly shown that humans are not as unique or central as we once assumed.

The same lesson may apply to consciousness. Rather than being a rare feature restricted to one specific type of biological organism, consciousness could emerge whenever evolution -- or something like it -- generates the right level of complexity.

What About Artificial Intelligence?

The paper naturally raises questions about AI, but the authors stop short of claiming that current AI systems are conscious.

Pober argues that the possibility of multiple conscious substrates does not mean every substrate can support consciousness. In his view, there is no reason to assume that today's computer hardware gives rise to conscious experience.

Schwitzgebel is somewhat more receptive to the possibility. He argues that once we reject the idea that consciousness requires human biology, it becomes harder to dismiss silicon-based systems simply because they are made of silicon rather than organic tissue.

More broadly, Schwitzgebel believes the debate has focused on the wrong question.

"It's focused too much on whether silicon can duplicate a human brain and not enough on the broader question of what kinds of systems can be conscious," he said.

The paper distinguishes between highly specific properties and broader categories. Asking whether human consciousness can be reproduced in a different substrate is a very specific question because human consciousness may depend on many details of human biology. Consciousness as a general phenomenon is a broader concept.

The authors compare this distinction to flight. Asking whether another creature can replicate an eagle's exact style of flight is different from asking whether flight itself can occur in other forms. Hummingbirds, bats, and insects all fly, but they do so in different ways.

Similarly, consciousness may take many forms throughout the universe without necessarily resembling human consciousness.

Does consciousness depend on flesh and blood?

The answer is almost certainly no, according to Eric Schwitzgebel, a distinguished professor of philosophy at the University of California, Riverside.