Scientists, I've come to realize, don't dwell much on their discoveries. They like to push forward into what they don't yet understand. Many will organize their whole career around a deep question that they may never be able to answer completely in their lifetime. They do backstrokes in a sea of unknowns.
The scientists who have made me appreciate this fact most are the ones who study the origin of life. We know life was on Earth at least 3.5 billion years ago. We know there was no Earth for life to be before 4.55 billion years ago. So how did life get its start in that first billion years?
It's a simple question, but its answer is profoundly challenging to find. Darwin himself shied away from it, because he could think of no way to address it as a scientist. There would be no place on Earth, he feared, where you could observe simple molecules reacting with each other and form the stuff of life. All those molecules would be devoured by the life that's already there.
But by the late 1900s, a small cadre of scientists had begun to develop ways to probe life's origins. In the early 1990s, when I was just starting out in the science writing business, I got to go to a conference where many of those scientists were meeting to discuss their work. There was Stanley Miller, who in 1953 had run a spark though a chamber filled with gases to see if lightning on the early Earth could form some of the building blocks of proteins. Four decades later, he was busy with a new set of experiments to test whether life might have started in an ocean covered in ice. I met other scientists at the meeting who studied ancient rocks on Earth and data sent back from space probes visiting distant planets. They were trying to narrow down the possible range of conditions that existed on the early Earth.
I was entranced. These scientists were merging information from many different sciences to test their ideas about how life began. I started writing about their work, and over the years I've tried to keep in touch to track their progress. Dropping by their labs or giving them a call feels like a reunion of sorts, a chance to catch up. They've never said to me, "Well, we've wrapped this one up in a neat bow. Time to find a new question." But that doesn't mean they haven't learned things.
For example, many scientists have argued that before there was DNA or protein, life was based on a molecule called RNA. (See here, here, and here for some of my articles in which I deal with the "RNA World" hypothesis in more detail.) While there's a lot of evidence that's consistent with an RNA World, scientists have long wondered how simple organic molecules on the early Earth could have spontaneously reacted to form such a complex molecules. The most obvious reactions by which RNA might form just didn't work.
John Sutherland and his colleagues at the University of Manchester decided that these results were not reason enough to reject the RNA World hypothesis. They began testing out new chemical reactions, and discovered a different route to RNA. It's as if they were trying to find a way from New York to Boston and found that I-95 was closed. Rather than just head back home, they discovered another highway. This discovery is important, and not just for the support it offers to a hypothesis about the origin of life. Just in terms of pure organic chemistry, Sutherland has discovered a pathway of chemical reactions that no one ever knew about before. Sutherland himself may move on to other aspects of the RNA World, but that discovery remains behind.
Indeed, as impractical as it may seem to explore the origin of life, some surprisingly practical discoveries have emerged over the years. David Deamer, a biochemist at the University of California at Santa Cruz, has long been interested in how life became encased in the first membranes (I first wrote about Deamer's work in 1995). He and his colleagues tried out various mixes of fatty acids to observe how well they could swallow up genetic molecules in bubbles. Protocells would need a way to get molecules in and out, and so Deamer and his colleagues tested different ways of embedding channels in their primitive membranes.
To Deamer's surprise, he found that he could drive a piece of DNA through the channel, a bit like pulling floss out of its package. Each nucleotide (a "letter" of DNA) can be identified as it emerges from the pore. Today, Deamer's investigation into the origin of life has morphed into a promising technology for sequencing DNA, known as nanopore sequencing.
If life did start out based on RNA, it would have to be possible for simple, RNA-based life forms to exist. How can you test a hypothesis like that? One way is to try to make that life from scratch. That's what Jack Szostak, a biologist at Harvard Medical School, has been trying to do for 20 years. I've written about Szostak a few times over the years, and I'm struck by his unflappable determination, no matter how far-fetched his research may sound. Step by step, he has improved a recipe for RNA molecules and the membranes that encase them. He can now mix together compounds that spontaneously turn into cell-like vesicles inside of which RNA molecules can grow.
If Szostak can create life (and many of his colleagues think he may very well do just that), he will not rest on his laurels. As sensational as it may seem to the rest of us, creating life is not actually his goal. It's just a means to another end--to answer the question of how life began. Creating life would be an important test of one hypothesis for life's origins, but that achievement would only provide Szostak with a new tool to probe the question more deeply. He will just keep backstroking further into his own scientific ocean.