The question took me by surprise. I was sitting in a noisy Boston café with two biochemists who were having a straight-faced conversation about putting together a budget to create synthetic life-forms. Next to me was Jack Szostak of Harvard Medical School, and across the table was Steven Benner, who had flown up from the University of Florida to pay Szostak a visit. The conversation was thrumming along, touching on the efficiencies of chemical reactions and the like, when Benner abruptly turned to me and asked, “How much do you think it would cost to create a self-replicating organism capable of Darwinian evolution?”
The question was not “Will we ever create life?” but simply how much money creating life would cost. “Twenty million dollars,” I said, choosing the number completely at random.
Benner nodded. “That’s what Jack says.”
Szostak, whose large glasses and round face make him look like an affable owl, had been letting Benner do most of the talking. Now he smiled, nodded with a slow blink, and said, “Sounds right.”
Sounds right? As we strolled back to Szostak’s lab, past the long lines of idling ambulettes parked by the Massachusetts General Hospital emergency room, I did some calculations in my head. Sequencing the human genome cost roughly $500 million, and essentially all that scientists had to show for the money was a long string of letters that make up human DNA. By contrast, for less money than a middling movie makes in a weekend, Szostak hopes to transform chemicals into a single-celled organism that will grow, divide, and evolve—and soon. “I think it’s conceivable it could be done in as little as three years,” he said. “The number of steps that might be real potential roadblocks has declined almost to zero.”
Courtesy of European Southern Observatory
The key chemical precursors of life are abundant throughout the universe in interstellar dust and molecular clouds like those found in the Chamaeleon I constellation (above). Scientists imagine the embryonic Earth forming from such clouds in the early days of our solar system, roughly 4.5 billion years ago. In the primordial welter of planetary formation, the fundamental chemistry of life begins with formaldehyde, water, hydrogen cyanide, and ammonia. During a period spanning millions of years, as the nascent Earth coalesces and solidifies from the dust, these molecules are brought together and concentrated at the planet’s surface. Comets and meteorites, which regularly shower the Earth prior to the formation of an atmosphere, scatter even more molecular seeds around the globe.
What’s more, Szostak’s goal is not just to create life from scratch. His ultimate objective is bigger: Find out how life began on Earth. The fossil record and modern genetic analysis suggest that humans and all other living species are descended from bacteria-like microbes that first appeared about 4 billion years ago. But bacteria, appearances notwithstanding, are very complex. They can be packed with thousands of genes, along with proteins and other molecules, working together in an intricate struggle to stay alive. Most scientists agree that such DNA-based life probably emerged from a much simpler life-form that no longer exists on Earth. Szostak wants to figure out what that first life-form was by building it (or something close to it) in his lab.
Szostak, 51, embarked on this quest to re-create the ancestor of us all because he was bored with yeast. After years of studying yeast genes in search of insights into how human DNA works, he was looking for a challenge. He found it two decades ago after a spectacular discovery upended conventional wisdom about ribonucleic acid, or RNA, one of the fundamental building blocks of life.
As the basic molecules of life move from space to a planetary environment, they begin to interact and undergo chemical reactions that produce larger and more complicated molecules. These larger molecules will ultimately become the building blocks of the earliest life-forms. The initial chemical reactions are highly unstable and require the aid of minerals to keep the newly formed organic building blocks from spontaneously degrading. Steven Benner, a biochemist at the University of Florida, theorizes that minerals containing borate may have acted as a catalyst in “stabilizing and guiding” these vital chemical processes. (See “Let There Be Borax,” Discover, May 2004, page 14.) Borate minerals are now commonly found in deserts such as Death Valley, California. Benner believes they were also abundant on the infant Earth.
Biochemists once viewed RNA as a lowly cellular messenger. Genes, made of double-stranded DNA, contain information for making proteins. This genetic code is embodied in long strings of chemical compounds called nucleotides and is copied onto RNA molecules, which then get shipped to ribosomes, biochemical factories where protein molecules are manufactured. Once completed, proteins curl up into complex shapes that let them do the actual work of life. Some proteins give an organism’s body its structure, whether in the cell’s internal skeleton or in a strand of hair. Other proteins, known as enzymes, can grab other proteins, cut them apart, or weld them to other proteins. DNA depends on enzymes to make new copies of its code as well as to translate it into RNA.
In the early 1980s Tom Cech, then a young biologist at the University of Colorado at Boulder, uncovered evidence that RNA does more than simply relay messages from DNA to proteins. In an experiment that earned him a Nobel Prize, he found that a single-celled creature named Tetrahymena possessed some RNA molecules that could act like simple enzymes. These molecules, which came to be known as ribozymes, twisted into a complicated snarl that allowed them to hack themselves apart. In other words, RNA could carry information like DNA and carry out biochemistry the way proteins do.