Scientists have proposed a radical new concept for defining life on Earth

About 3.5 billion years ago, life on Earth originated from a molecular beginning and, over time, evolved into the impressive array of creatures we know today. This is the modern line of reasoning. But we still have no clear definition of life. For example, is a virus a living thing? Or an entire forest ecosystem? After all, many aspects of an ecosystem are as dependent on each other as the organs within the body.

So biologist Chris Kempes and complex systems researcher David Krakauer of the Sante Fe Institute in New Mexico put forward the idea that our focus on evolution as the driving force behind life may have “blinded us to additional general principles of life.”

To explore this question, the researchers expanded the definition of life to combine two energetic and informational processes that can encode and transmit adaptive information forward in time.

Using this definition greatly expands the concept of “life” to include such concepts as culture, forests, and economics. A more traditional definition might see these as products of life rather than life itself.

“Human culture lives on the material of the mind, just as multicellular organisms live on the material of single-celled organisms,” Kempes explains.

Based on their new definition, the researchers argue that life has arisen on Earth many times, and that we actually coexist with many forms of current life.

The system proposed by Kempes and Krakauer has three hierarchical levels of limitations on what life implies, as shown below.

At the first level, life is limited by the possible materials from which it can be formed (e.g., molecules). At the second level, life is limited by the constraints of the surrounding universe (e.g., gravity), and at the third level, life is optimized by adaptive processes (e.g., natural selection).

Within this hierarchy, concepts that unify the world of physics and biology are considered. For example, life uses many options for energy production, using the constraints of the first level, but all must adhere to the constraints of the second level of the law of thermodynamics.

“No single cell will contain more internal structure than can be accounted for by the total free energy available from the environment,” the team writes in their paper.

“We expect that many rich biological concepts will be defined by a ‘strange tangle’ of three levels, because these three levels will inevitably co-evolve.

This theory fully conceives of life as a spectrum rather than a discrete phenomenon, e.g., what makes us individuals? Only cells born from the same DNA, or our microbiome too? Not to mention the fluid connections between environmental energy, cellular physiology, and evolutionary processes.

While all of this may be as mind-bogglingly theoretical as much of quantum physics, it is a fascinating attempt to look at an old concept from a new perspective. In complex systems, such as life and the consequences of our lives, sometimes expanding our thinking can trigger different ideas that lead to new insights.

The authors hope that this broader view can lead to an understanding of exactly what we mean by life, help create devices to create or search for it, and understand the level of life we observe–even if it is radically different from the life we are used to on Earth.

Their definition would certainly put an end to the debate about whether viruses are really alive, since they fit well into Kempis and Krakauer’s theory of life.

While this schema is certainly detailed and gives us a lot of food for thought, changing definitions is hard work. And when most of us think about life, it is likely to be only about biological life-at least until we meet aliens who challenge biology as we know it, or until our artificial intelligences are advanced enough to form their own minds.

“We argue that we will be able to say we have a new theory of life when it can reveal to us many origins and many types of life,” they write.

This theory was described in the Journal of Molecular Evolution.

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