Astrobiologist Stuart Bartlett discusses a new framework for defining life based on dissipation, autocatalysis, homeostasis, and learning. The importance of defining life for scientific understanding, complexity saturation in artificial life, overcoming cooperation barriers, and the role of auto-catalysis in regulating multicellular organisms are also explored.
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Quick takeaways
Life should be defined based on a collection of life-like properties rather than a unified concept.
The current definition of life is limited and needs to consider alternative forms that may not rely on Earth-centric characteristics.
Exploring subsets of life-like systems can provide insights into the range of possibilities for life and inform the search for life beyond Earth.
Deep dives
The Definition of Life: Exploring the Core Features
The podcast explores the definition of life, focusing on the core features that make something qualify as life. The guest, Stuart Bartlett, discusses how the current definition of life might be too Earth-centric and limited. He highlights the importance of considering alternative forms of life that may not rely on the same characteristics as life on Earth, such as chemically-based and evolving. The discussion delves into the concept of learning and its role in determining the boundaries of life. Examples of disruptive structures like convection cells and pattern-forming chemical systems are mentioned to illustrate systems that exhibit some features of life but do not meet all the criteria. The conversation concludes by discussing how understanding the definition of life can aid in studying the origin of life on Earth and searching for life elsewhere in the universe.
The Challenges of Defining Life
Examining the NASA definition of life as a self-sustaining chemical system capable of Darwinian evolution, the limitations and controversies surrounding this definition are discussed. The guest argues that there is a lack of consensus in the field of astrobiology about what should define life, and whether evolution by natural selection alone is sufficient to explain the complexity of life on Earth. The conversation raises questions about the emergence of social behavior in insects, which challenges the traditional Darwinian perspective. Alternative approaches to understanding evolution, such as viewing it as a large associative learning system, are also explored. The discussion emphasizes the need for a definition of life that goes beyond Earth-centric assumptions and remains open to the possibility of different forms of life.
Exploring the Subset of Life-like Systems
The conversation examines different subsets of life-like systems that possess some but not all of the core features of life. Examples of systems like convection cells and hurricanes are provided, which demonstrate dissipation and autocatalysis without displaying learning or homeostasis. It is highlighted that while these systems exhibit energy transfer and self-organization, they lack the capacity to process information and actively utilize it. The importance of understanding these subsets of life-like systems is emphasized, as it can provide insights into the range of possibilities for life and inform the search for life beyond Earth.
Chemical reactions that exhibit life-like behaviors
There are artificial chemical systems, such as the Selkov reaction, that demonstrate life-like behaviors. By reacting specific molecules under different parameter settings, these reactions can produce elaborate patterns resembling replicating bacteria. While these chemical systems exhibit reproduction and growth, they lack evolution and limited heredity.
Cooperative behavior and learning in simple chemical systems
Studies have shown that simple chemical systems can exhibit cooperative behavior and even regulate their temperature in response to thermal changes. This suggests a form of learning in these systems. For example, in experiments with oil droplets, they demonstrate chemotaxis and can solve mazes. These chemical systems, although not alive, show self-replication, homeostasis, and the ability to adapt to previously inhospitable environments, making them intriguing models to study the emergence of life-like behaviors.
Someday, most likely, we will encounter life that is not as we know it. We might find it elsewhere in the universe, we might find it right here on Earth, or we might make it ourselves in a lab. Will we know it when we see it? “Life” isn’t a simple unified concept, but rather a collection of a number of life-like properties. I talk with astrobiologist Stuart Bartlett, who (in collaboration with Michael Wong) has proposed a new way of thinking about life based on four pillars: dissipation, autocatalysis, homeostasis, and learning. Their framework may or may not become the standard picture, but it provides a useful way of thinking about what we expect life to be.
Stuart Bartlett received his Ph.D. in complex systems from the University of Southampton. He is currently a postdoctoral researcher in the Division of Geological and Planetary Sciences at Caltech, and was formerly a postdoc at the Earth Life Science Institute at the Tokyo Institute of Technology.