… some of them will stick? This month’s issue of The Scientist offers a look at “some of the most current origin-of-life science, from new research on how RNA may have been assembled from precursor molecules to what we now know about our last universal common ancestor.” That ancestor, we are assured, is “not [Darwin’s] ‘primordial form,’ but rather a sophisticated cellular organism that, if alive today, would probably be difficult to distinguish from other extant bacteria or archaea.”
So one and a half centuries of research have not yet turned up a single entity that, like Thomas Huxley’s hoped-for Bathybius haeckelii, is on its way to becoming life? Hardly for lack of trying! Here is a whirlwind tour of the waterfront:
Arsenic world: In December 2010, NASA researchers reported that they had taught microbes to metabolize arsenic instead of phosphorus, demonstrating that life could arise from unexpected chemicals, perhaps elsewhere in the galaxy. (Some researchers have suggested chlorine life instead.) Most researchers were unconvinced. In 2011, Science published eight articles questioning NASA’s study in a single edition and arsenic-based life featured as one of The Scientist‘s top ten scandals of 2011.
Clay world: Some theorists argue that clay (or clay hydrogels) can select for molecules that can self-organize. The Scriptural associations of clay were a gift to science writers; the details did not impress researchers. Information theorist Hubert Yockey pointed out that clay crystal structures just repeat the same information indefinitely. By contrast, life’s minimum information density is somewhere around the level of DNA. OOL theorist Leslie Orgel (1927-2007) said it wouldn’t work for RNA either: If clay had the structural irregularities needed to enable RNA to emerge, it probably wouldn’t reproduce it accurately.
Lagoons on the early Earth: Stanley Miller (1930-2007) of the textbooks’ Miller-Urey experiment believed that the conditions on early Earth’s beaches could foster pre-life reactions because chemicals would concentrate more there than out at sea. But Robert Shapiro, proponent of the “metabolism first” model, complained that “a large lagoon would have to be evaporated to the size of a puddle, without loss of its contents, to achieve that concentration. This process is not thought to occur today.” He added, with an apparent touch of impatience,
The drying lagoon claim is not unique. In a similar spirit, other prebiotic chemists have invoked freezing glacial lakes, mountainside freshwater ponds, flowing streams, beaches, dry deserts, volcanic aquifers and the entire global ocean (frozen or warm as needed) to support their requirement that the “nucleotide soup” necessary for RNA synthesis would somehow have come into existence on the early Earth.
Metabolism first: Robert Shapiro (1935-2011) questioned Leslie Orgel’s RNA world because of “the extreme improbability” that such a long, complex molecule as RNA would spontaneously arise and initiate life. His doubts earned him the title, Dr. No. Aspiring to somehow become Dr. Yes, he offered a model that life began via small molecules with a simple metabolism and progressed from there, hence “metabolism first.” He hoped, among other things, to vindicate the idea that “There’s nothing freaky about life; it’s a normal consequence of the laws of the universe.”
Researcher Eric Smith, a physicist at the Santa Fe Institute, offers a more recent model of early metabolism: “It seems likely that the earliest cells were rickety assemblies whose parts were constantly malfunctioning and breaking down. … How can any metabolism be sustained with such shaky support? The key is concurrent and constant redundancy.” Or “millions of years of a poor replicator”, as a summary article in Science put it, leaving unclear how hits could have mattered in those days but misses didn’t.
“RNA first” proponent Leslie Orgel responded irritably to Shapiro’s metabolism first model, “solutions … dependent on ‘if pigs could fly’ hypothetical chemistry are unlikely to help.” Near the end of his life, Orgel had perhaps forgotten that he himself once co-authored a paper with Francis Crick speculating that extraterrestrials might have started life.
Numerous less publicized models wallop through the science press, on the hope, perhaps, of a lucky strike: For example, not-obviously-promising substances such as hydrogen, ammonia, hydrogen cyanide, formaldehyde, or peptides, possibly kick started life. Maybe metals acted as catalysts. Or mica sheets. Otherwise, cold temperatures or ice helped life get started, despite the fact that cold reduces chemical reaction speed. Or a high salt environment. Or hot springs. No surprise that science writer Colin Barras observes that origin of life is “a highly polarised field of research.” Most fields have only two poles, not twenty.
One model is noteworthy for the fact that it is the closest that origin of life theorists have come so far to an ancient pagan creation myth. Yet it was published in a popular science magazine (New Scientist):
Once upon a time, 3 billion years ago, there lived a single organism called LUCA. It was enormous: a mega-organism like none seen since, it filled the planet’s oceans before splitting into three and giving birth to the ancestors of all living things on Earth today. … LUCA was the result of early life’s fight to survive, attempts at which turned the ocean into a global genetic swap shop for hundreds of millions of years. Cells struggling to survive on their own exchanged useful parts with each other without competition — effectively creating a global mega-organism.
How did it all work? “It was more important to keep the living system in place than to compete with other systems.”
Really? More important for whom? Who then existed for life to be more important to? The mega-organism itself? But that would imply selfhood and purpose. If selfhood and purpose were present at the origin of life, why is design a problem and not a solution?
Editor’s Note: Here are links to the whole “Science Fictions Origin of Life” series.
Photo source: TheGiantVermin/Flickr.