Lyfe

As the origins-of-life research community grows, we see more offshoots examining “life as we don’t know it”. Whether you’re studying the creation of synthetic life or figuring out how to detect a reasonable biosignature for a Mars missions, it helps to have a working definition of life that’s perhaps broader than “life as we know it” here on Planet Earth. The latest foray comes from Bartlett and Wong in their recent article “Defining Lyfe in the Universe: From Three Privileged Functions to Four Pillars” (Life 2020, 10, 42, doi:10.3390/life10040042). Life is an open-access journal so you can read the article in full for yourself.

Yes, they call it Lyfe. No, it’s not a typo.

First, the motivation. Your definition of life will affect how you detect it. Complicating matters is that “life is a verb, not a noun” (the title of Russell’s article in Geology 2017, 45, 1143-1144). Lane has also argued that “what is life?” is the wrong question, rather it should be “what is living?” So if you think life requires Darwinian evolution (per the NASA definition), then something that exhibits Lamarckian or some other type of evolutionary process will be discarded by definition. That might be problematic because Earth life provides a sample size of one. Our Terran view might be very myopic.

Competing hypotheses have always been a part of the origins-of-life research community. They can be categorized by “what came first?” or alternatively “what is foundationally crucial?” questions. While amino acids can be easily synthesized from simple molecules under a variety of conditions, making functional proteins from such prebiotic soup mixtures was and still remains very challenging. The RNA World hypothesis provided a possible way out, and is the reigning paradigm of the Genes-First camp. The rival Metabolism-First camp has picked up more adherents over time and has been gaining ground, while the Lipid World (Compartments-First camp) has always been acknowledged as important, but perhaps peripherally so with fewer researchers working in that area. These are the Three Privileged Functions outlined by Bartlett and Wong.

However, the three hypotheses could sample a very small space in the grand scheme of Lyfe out there in the universe. Bartlett and Wong provide some very useful visual aids for the reader to understand why, one of which is shown below. The many pink-lavender arrows represent such hypotheses aimed at discovering the trajectory of life on Earth. Synthetic approaches (orange dotted lines), not necessarily aimed at prebiotic plausibility, may provide further routes both to extant life and to artificial/alien life (as we don’t know it). And there might be yet other paths to other types of alien life or subsets thereof.

The broader Lyfe, the authors argue, should have four pillars: (1) Dissipation (due to free energy and the second law of thermodynamics), (2) Autocatalysis (for exponential growth), (3) Homeostasis (to maintain some unity amidst a changing environment), and (4) Learning (to not just survive, but to thrive!). They provide several examples of how these pillars may feature in different types of lyfe or sub-lyfe-forms; they also try to avoid privileging one pillar over others, although it is clear that without free energy, it’s difficult (although not impossible) to do anything else.

I’ve read many conceptual origin-of-life papers, and while there’s nothing earth-shattering about Bartlett and Wong’s approach, I particularly appreciated the Figures in the paper. These do an excellent job communicating the authors’ arguments, better than in many other cases where the reader just gets bogged down in text and technicalities. I smiled at their choice of colors to illustrate the three privileged functions (replication, metabolism, compartments) because the exact same three colors (blue, red, yellow) are used for those same three functions in the origin-of-life game Bios Genesis. (Green, the fourth color in the game, represents negentropy – related to dissipation.)

As I’m preparing to teach a special topics origins-of-life chemistry course this coming semester, I’ve been considering adding a “search for life outside Earth” component, and this paper might be one that I will assign. It’s nice to find well-written articles that will be accessible to undergraduates for a class.