An Amazon of words flowed from Charles Darwin's pen. His books covered the gamut from barnacles to orchids, from geology to domestication. At the same time, he filled notebooks with his ruminations and scribbled thousands of letters packed with observations and speculations on nature. Yet Darwin dedicated only a few words of his great verbal flood to one of the biggest questions in all of biology: how life began.
The only words he published in a book appeared near the end of On the Origin of Species: "Probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed," Darwin wrote.
The Origin of Life - Abiogenesis
Darwin believed that life likely emerged spontaneously from the chemicals it is made of today, such as carbon, nitrogen, and phosphorus. But he did not publish these musings. The English naturalist had built his argument for evolution, in large part, on the processes he could observe around him. He did not think it would be possible to see life originating now because the life that's already here would prevent it from emerging.
In 1871, he outlined the problem in a letter to his friend, botanist Joseph Hooker: "But if (and Oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc., present, that a protein compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed."
Scientists today who study the origin of life do not share Darwin's pessimism about our ability to reconstruct those early moments. "Now is a good time to be doing this research, because the prospects for success are greater than they have ever been," says John Sutherland, a chemist at the University of Manchester in the United Kingdom. He and others are addressing each of the steps involved in the transition to life: where the raw materials came from, how complex organic molecules such as RNA formed, and how the first cells arose. In doing so, they are inching their way toward making life from scratch. "When I was in graduate school, people thought investigating the origin of life was something old scientists did at the end of their career, when they could sit in an armchair and speculate," says Henderson James Cleaves of the Carnegie Institution for Science in Washington, D.C. "Now making an artificial cell doesn't sound like science fiction any more. It's a reasonable pursuit."
Life--or at least life as we know it--appears to have emerged on Earth only once. Just about all organisms use double-stranded DNA to encode genetic information, for example. They copy their genes into RNA and then translate RNA into proteins. The genetic code they use to translate DNA into proteins is identical, whether they are emus or bread mold. The simplest explanation for this shared biology is that all living things inherited it from a common ancestor--namely, DNA-based microbes that lived more than 3.5 billion years ago. That common ancestor was already fairly complex, and many scientists have wondered how it might have evolved from a simpler predecessor. Some now argue that membrane-bound cells with only RNA inside predated both DNA and proteins. Later, RNA-based life may have evolved the ability to assemble amino acids into proteins. It's a small step, biochemically, for DNA to evolve from RNA.