Each scientific discipline has its own practices, its own language, its own body of literature, its own snooty opinion of neighboring disciplines and its own notion of where it stands along perceived intellectual hierarchies, so perfectly illustrated by this typically excellent XKCD comic. At the fuzzy boundaries between disciplines there are blended fields—physical chemistry, chemical biology, biological anthropology—and emerging disciplines like my own field of synthetic biology (a different kind of applied biology). It's often difficult to know exactly when you've crossed the boundary from one discipline into the next, but from the inside looking out it's much easier to draw the boundaries of your own field.

This has all been on my mind as I think about chemistry for chemistry day here at the Scientific American blogs. Organic chemistry, chemical biology, and biochemistry are enormous and enormously rich fields that blend together chemistry and biology, but what separates "applied chemistry" like biology and "pure" chemistry? All cells are made of chemicals, but when do collections of chemicals become alive?

This is a big question, and one that is central for a small group of researchers working between chemistry and biology studying the origin of life on earth. For many of these researchers, trying to understand how life started billions of years ago means trying to recreate that difficult to define transition from a collection of chemicals to a living thing. But before you start mixing chemicals together, you have to decide on what your definition of life is going to be in the first place. A recent New York Times article describes work in this field and introduces the discussion about what defines life:

Biologists do not agree on what the definition of life should be or whether it is even useful to have one. But most do agree that the ability to evolve and adapt is fundamental to life. And they also agree that having a second example of life could provide insight to how it began and how special life is or is not in the universe, as well as a clue for how to recognize life if and when we do stumble upon it out there among the stars.

Indeed, the most common definition used by biologists comes from NASA, defining life as "a self-sustained chemical system capable of undergoing Darwinian evolution." The article goes on to describe work by Gerald Joyce's lab at the Scripps Research Institute in San Diego that seems to have partially achieved these basic requirements for life in a test tube. The chemical systems they design are collections of RNA strands that can join together two smaller pieces of RNA into the shape of the original strand. Different RNA molecules can have errors in their sequence and compete for the same pool of smaller pieces, setting up a situation where the molecules can evolve. Are these collections of replicating and evolving molecules alive? Most people would say no (not yet?), but perhaps they exist somewhere along a scale of "aliveness" that connects chemicals and life.

At this point in our exploration of the boundary between chemistry and biology we've run into another fuzzy boundary, one between biology and philosophy. Can something be partially alive? What does 50% alive look like? What discipline will emerge when we try to understand these questions that arise when synthetic biologists make life-like cells with useful functions? James King is a speculative designer who explores these questions in his work at the boundaries between science and art, life and non-life. His Cellularity project proposes a scale of aliveness for synthetic organisms created by the future pharmaceutical industry:

Art can bring these questions to life, and bring life to chemicals in different ways. Rachel Armstrong is a researcher who explores how living technologies and smart chemistry can be used to make sustainable architecture, using protocells—droplets of oil in water that can resemble cell membranes—as a tool for depositing paints or hardening surfaces, but also as a way to push the boundaries of what we consider alive. Her film follows the lives of protocells as they wiggle through the water:

When I first saw this film at the Bio:Fiction film festival in Vienna I was mesmerized by the strangely beautiful motion of the protocells, but the anthropomorphizing subtitles made me uncomfortable. How can a droplet of oil in water feel anything, want anything, love anything? These words mean something in human contexts, but they can get us into trouble when we try to apply them to other biological phenomena, particularly evolution (evolution never wants anything). But perhaps my discomfort was also because the subtitles made the random motions of the protocells seem intentional, made the bubbles really seem alive. I felt sad when one of them "died," happy when they were "in love." The words were enough to spark real human feelings, making the protocells pass some kind of emotional Turing test (much like the fabulous scene with children holding Furbies upside down on a recent RadioLab episode). Just seeming alive places them somewhere on that uneasy and complicated scale between life and non-life, and maybe that's alive enough.