What has been overturned: the old cellular definition of life
For decades, the standard answer to 'what is life?' was rooted in cell theory: life is made of cells that can grow, reproduce, and respond to their environment. But recent discoveries have cracked that foundation. The discovery of giant viruses—which are larger than some bacteria and have complex genomes—blurred the line between viruses (usually considered non-living) and cellular life [1]. At the same time, scientists began building artificial cells in the lab that can perform life-like functions, such as compartmentalizing reactions and even dividing [2][4]. These advances have led some researchers to argue that the old question 'What is life?' should be replaced with 'What are lives?'—implying that multiple forms of life may exist on Earth and beyond [1].
A 2021 study directly tested whether a single set of criteria could define all known life forms. Using a statistical modeling approach based on family resemblance (like how we recognize a chair without a strict definition), the researchers found that living and non-living entities can be grouped by overall similarity, but no single checklist works for every case [3]. This means that artificial cells—which share some but not all features of natural cells—fall into a gray zone that the old definition cannot handle.
What we know now: artificial cells show life-like behavior but are not fully alive
Artificial cells today are sophisticated compartments that mimic key aspects of life. A 2017 review identified five criteria of life—such as self-organization, metabolism, growth, reproduction, and evolution—and showed that artificial cells can integrate several of these, including complex adaptive behavior [2]. For example, some artificial cells can sense their environment and change their activity in response, a hallmark of living systems [2]. Another 2020 review highlighted that artificial cells can host cell-free systems that carry out transcription and translation—the processes that turn DNA into proteins—inside synthetic compartments [4]. This means they can perform the basic molecular work of life, but they still depend on externally supplied materials and energy.
However, no artificial cell yet meets all five criteria of life simultaneously. They can grow and divide, but their metabolism is not self-sustaining; they rely on pre-made building blocks [2][4]. A 2016 review noted that there are many different forms of artificial cells with many different definitions, reflecting the fact that the field is still exploring what counts as 'life-like' [5]. So, artificial cells are changing how we define life by showing that life is not a binary switch (alive vs. not alive) but a spectrum of properties.
What this means for defining life: a shift from one definition to many
The big takeaway is that artificial cells are not forcing us to throw out the concept of life—they are forcing us to expand it. Instead of a single definition, scientists are moving toward a family resemblance approach, where an entity is considered alive if it shares enough features with known life forms, even if it lacks some [3]. This is useful for classifying novel entities like synthetic cells, intelligent robots, or extraterrestrial life [3]. The 2022 paper by Greco Hernández explicitly argues that we may now be facing a scenario where several types of life exist on Earth—natural cells, giant viruses, and synthetic cells—each with different degrees of 'aliveness' [1].
In practical terms, this means that the question 'Could artificial cells change how we define life?' is already being answered with a 'yes.' The change is not that artificial cells are fully alive, but that they have revealed the old definition to be too narrow. As the 2017 review put it, artificial cells display 'life-like functionality and adaptivity' [2]—enough to challenge our assumptions, but not enough to settle the debate. The evidence across these papers converges on the same conclusion: life is not a single category but a spectrum, and artificial cells are helping us map that spectrum.
About These Sources
This answer is built on 5 peer-reviewed studies — published from 2016 to 2022, 1 in Q1 journals, collectively cited 1,299 times — selected as the most relevant from 5 studies that passed quality screening, drawn from 23 papers retrieved from a database of over 500 million.
Sources used in this answer
Schrödinger and the Possible Existence of Different Types of Life
Argues that giant viruses and synthetic cells challenge the cellular definition of life, proposing that multiple types of life may exist on Earth and the universe, shifting the question from 'What is life?' to 'What are lives?'
Artificial cells: synthetic compartments with life-like functionality and adaptivity
Reviews artificial cells that integrate life-like characteristics such as self-organization, growth, reproduction, and adaptive behavior, but notes that no artificial cell yet meets all five criteria of life simultaneously.
The problem of defining life: a case study
Using a statistical family resemblance model, finds that no single set of criteria can define all known life forms, and that living and non-living entities can be grouped by overall similarity, making it difficult to classify novel forms like artificial cells.
Compartmentalizing cell-free systems: toward creating life-like artificial cells and beyond
Reviews artificial cells that host cell-free systems for transcription and translation inside synthetic compartments, showing progress toward assembling a fully synthetic cell but noting current dependence on external materials.
Artificial cells: from basic science to applications
Notes that there are many different forms of artificial cells with many different definitions, reflecting the field's ongoing exploration of what constitutes life-like behavior.