A new theory draws from physics and biology to better explore complexity and evolution in nature. (Image: Anna Tanczos/Sci-Comm Studios)

An international team of researchers has developed a new theoretical framework that bridges physics and biology to provide a unified approach for understanding how complexity and evolution emerge in nature. This new work on "Assembly Theory," published today in Nature, represents a major advance in our fundamental comprehension of biological evolution and how it is governed by the physical laws of the universe.    

This research builds on the team's previous work developing assembly theory as an empirically validated approach to life detection, with implications for the search for alien life and efforts to evolve new life forms in the laboratory. In prior work, the team assigned molecules a complexity score —  called the molecular assembly index — based on the minimal number of bond-forming steps required to build a molecule. They showed how this index is experimentally measurable and how high values correlate with life-derived molecules.    

The new study introduces mathematical formalism around a physical quantity called "Assembly" that captures how much selection is required to produce a given set of complex objects, based on their abundance and assembly indices.    

"Assembly theory provides a completely new lens for looking at physics, chemistry, and biology as different perspectives of the same underlying reality," explains lead author Sara Walker, a theoretical physicist and origin of life researcher from Arizona State University and External Professor at the Santa Fe Institute. "With this theory, we can start to close the gap between reductionist physics and Darwinian evolution — it's a major step toward a fundamental theory unifying inert and living matter."    

The research team, which also includes SFI Professor Christopher Kempes and SFI External Professor Michael Lachmann, demonstrated how assembly theory can be applied to quantify selection and evolution in systems ranging from simple molecules to complex polymers and cellular structures. It explains both the discovery of new objects and the selection of existing ones, allowing open-ended increases in complexity characteristic of life and technology.    

"Assembly theory provides an entirely new way to look at the matter that makes up our world, as defined not just by immutable particles but by the memory needed to build objects through selection over time," says Lee Cronin, a chemist from the University of Glasgow and co-lead author. "With further work, this approach has the potential to transform fields from cosmology to computer science.  It represents a new frontier at the intersection of physics, chemistry, biology, and information theory."    

The researchers aim to further refine assembly theory and explore its applications for characterizing known and unknown life and testing hypotheses about how life emerges from non-living matter. “A  key feature of the theory is that it is experimentally testable,” says Cronin. “This opens up the exciting  possibility of using assembly theory to design new experiments that could solve the origin of life by  creating living systems from scratch in the laboratory.”    

The theory opens up many new questions and research directions at the boundary of the physical and life sciences. Overall, assembly theory promises to provide profound new insights into the physics underlying biological complexity and evolutionary innovation.  

Read the paper "Assembly theory explains and quantifies selection and evolution" in Nature (October 4, 2023.) doi: 10.1038/s41586-023-06600-9.


More Information:

  • "A key challenge in understanding the evolution of life is dealing with the huge space of possibilities and combinations, and assemply theory gives us a way to spot evolutionary processes as the construction of complicated objects." — SFI Professor Christopher Kempes
  • "Life is defined by an evolutionary process. To find life, we should find evolution, and luckily the process of construction of objects and molecules with and without evolution is totally different. Evolution will discover an assembly plan and then build the same object again and again, or reuse it in more complex objects. Once evolution is involved, we are dealing with the dynamics of assembly plans and not of particles.“ —SFI External Professor Michael Lachmann
  • Visit SFI's webpage on Laws of Life
  • Read the paper "Assembly theory explains and quantifies selection and evolution" published in Nature Communications on October 4, 2023, by Lee Cronin and Sara Walker
  • Read the essay "Time is an object" published in Aeon on May 19, 2023, by Lee Cronin and Sara Walker