assembly theory, a way of differentiating life from nonlife, not by its chemistry but by its complexity.

Traditionally, science seeks order by understanding the simplest parts of a system. How does a single gas particle behave given a certain temperature? Which gene in our DNA determines eye color? Scientists then try to develop theories that explain more general observations based on their detailed understanding of the individual parts.

“This phenomenon, in which components join together to form larger, stable structures having new properties that could not have been predicted from the characteristics of the individual parts, is known as self-assembly. It is observed at many scales in nature. In the human body, for example, large molecules self-assemble into cellular components kn

Arguably it is here that we begin to see how life is not a mechanical process that transmits information and organization steadily and predictably along linear pathways from genes to ever increasing scales. Instead it is a cascade of processes, each with a distinct integrity and autonomy, the logic of which has no parallel outside the living world.

If those molecules bump together and form something more complex, on and on, Cronin said, “that is the selection equivalent of gravity. And that process of complexity generates everything we have in the universe that’s associated with life.”