What constitutes life, and how did it originate?

Life likely emerged from nonliving matter aided by asteroids striking a turbulent, chaotic Earth.

Natural selection may not be the primary driver of adaptive evolution.

Self-organizing molecules slowly acquired memory, agency, and, eventually, consciousness.

I watch Rufus, a friend’s dog, chew enthusiastically on a rubber bone. I know the dog is alive, and his toy is not. I know that intuitively. But can I prove it scientifically? Can science parse the distinction between life and inert matter?

To be considered alive, does something have to be able to reproduce, move, grow, and process energy? Any definition along these lines is riddled with exceptions. For instance, is a virus alive? While viruses do evolve, they don’t replicate on their own. They use the host’s tissues to make copies of themselves.

In Star Trek: The Next Generation, the definition of life as something that “absorbs compounds from its environment,” “excretes waste,” and “grows” is famously challenged by characters like Data to show its limitations. Fire or crystals, for example, also consume nutrients, which are energy, “excrete” waste, and grow, yet are not considered alive. Throughout Star Trek, the ultimate definition of life, particularly when discussing androids or artificial intelligence, often centers on sentience, consciousness, and self-awareness rather than just biological or metabolic functions. However, these are abstract concepts that are difficult if not impossible to define scientifically.

One of science’s most enduring riddles is what constitutes life and how cells that metabolize, replicate, and adapt emerged from matter that was once inert. Many scientists speculate........

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