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 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 a complexity score to molecules 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," explained lead author Sara Walker, a theoretical physicist, origin of life researcher and professor with appointments in Arizona State University's School of Earth and Space Exploration, Biosocial Complexity Initiative, Center for Social Dynamics and Complexity (CSDC), Biodesign Center for Mechanisms of Evolution and the Beyond Center.

"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."

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