Is Assembling Life Like Assembling LEGOs?
I recently read Sara Walker’s new book, Life as No One Knows It: The Physics of Life’s Emergence. The book is addressed to a popular audience, and although the term is barely used, it is really about assembly theory in origin of life research. Walker asks questions like, What is Life? (with no definitive answer), and calls the origin of matter and the origin of life two hard problems in science. Walker mostly tackles the latter through her explication of assembly theory, but with questionable success.
Illustrating with LEGO Blocks
Because the book is aimed at a popular audience, Walker has the difficult task of explaining technical concepts in ways accessible to general readers. Thus, she resorts to the analogy of LEGO blocks to illustrate how complex structures can be assembled by combining simpler structures through a process called selection. Two LEGO blocks can be combined in only a small number of ways. But as a LEGO figure grows larger, the number of ways to attach new blocks quickly inflates. Randomly attaching new blocks to a complex figure will likely not produce a useful or meaningful figure. But a process of selection at each step can cut a path through this inflating combinatorial space toward the creation of a complex and meaningful figure.
According to Walker, this is how life originated. She writes:
The origin-of-life transition occurs when the combinatorial explosion of possible low assembly molecules gets constrained and funneled to select only a subset of possible molecules. Those are scaffolded to build more assembled objects, where those objects in turn build even more assembled ones. It captures the idea that it is objects building slightly more complex objects all the way down. As Lee [Cronin] sometimes says, to solve the origin of life all we need is to generate a simple machine that can build a slightly more complex machine, and so on. (163)
Unfortunately, Walker provides no clue as to what process does all the “constraining,” “funneling,” and “scaffolding.” And what characteristic marks the non-life-to-life transition if we don’t have a good working definition of life in the first place? Moreover, if Lee Cronin is successful in generating a machine capable of generating more complex machines, it will be Cronin’s intelligence standing at the head of this process. What undirected process would be capable of generating the original machine-generating machine? I came away from Walker’s book with far more questions than answers.
Refreshingly Transparent
To Walker’s credit, however, she is refreshingly transparent on one crucial point. In a discussion of homochirality in organic molecules, she freely admits, “We do not know the mechanism by which this property first arose for the life we observe on Earth.” (173) She does go on to state her hope that assembly theoretic principles might eventually “shed new light on what has been a stubborn mystery.” (173) I wouldn’t bet the house on it. And without a naturalistic explanation for homochirality, one can never have a naturalistic explanation for the origin of life.
One other stylistic feature of Walker’s book is worth mentioning. Against all literary convention, she insists on referring to other scientists by their first names after the first reference where she provides the full name. So, we are regularly treated throughout the book to references to conversations Walker has had with people like Paul, or Lee, or Andy, leaving the reader to scramble to remember that these are references to Paul Davies, Lee Cronin, and Andrew Ellington. I don’t know if she is trying to impress the reader by showing that she is on a first-name basis with all these scientists. But this stylistic decision can be confusing and undercuts the professionalism of the book (I’m surprised the publisher allowed it).
In all honesty, I wouldn’t recommend spending time reading Life as No One Knows It. Sara is well-versed in physics and chemistry, yet she is just as clueless on the origin of life as every other scientist trying to explain it in purely naturalistic terms.
