Charles Darwin’s theory of how life evolves through natural selection was first published more than 140 years ago. It’s a simple, elegant hypothesis with enormous power to explain the world we live in, yet paradoxically it remains misunderstood or ignored by many nonscientists. Indeed, as Steve Jones points out in Darwin’s Ghost, Charles Darwin’s magnum opus, The Origin of Species by Means of Natural Selection, is rarely read today. Nevertheless, the concept of Darwinian natural selection is still exerting an ever-expanding influence in a surprisingly broad range of academic disciplines.
In his opening pages Jones gives us a concise account of how natural selection works: “Errors of descent”—Jones’s shorthand for genetic variation caused by mutation—
are the stuff of evolution. Variation in the ability to copy them—natural selection—gives it a direction. Nature does not favor beauty, or strength, or ferocity; all it can do is to advance those best able to multiply themselves. Although its products include the most beautiful and most repulsive of beings there is no mystery to Darwin’s machine: it is no more than genetics plus time.
Jones calls natural selection “the factory for the almost impossible.” The concept is an important one, for the seemingly improbable idea that such complex organs as the eye result from evolution has long been a stumbling block to acceptance of Darwin’s theory for many. Jones writes that not only is the eye the result of evolution, but that
the eye happened…fifty times, and the problem of how to extract information from light has been solved in a dozen ways. The eye is as intricate as it needs to be, and no more. Its apparent perfection does not destroy but upholds the theory of evolution.
That is, the eye, in its various versions from fly to primate, improved the ability of very different creatures to multiply.
For George Bernard Shaw such explanations diminished the world. “When its [natural selection’s] whole significance dawns on you, your heart sinks into a heap of sand within you. There is a hideous fatalism about it, a ghastly and damnable reduction of beauty and intelligence, of strength and purpose, of honour and aspiration.” Perhaps such feelings are part of the reason why Darwin’s idea has met such resistance in the popular mind.
The desire to know how life began has been one of humanity’s enduring passions, and until the publication of Christopher Wills and Jeffrey Bada’s The Spark of Life, no explanation I know of has included natural selection as a factor. Indeed, as they make clear, until the nineteenth century investigations into life’s origin always mixed observation of the natural world with a touch of the divine. The Spark of Life commences with an engaging overview of these early researches. One of the first to approach the problem in a systematic manner was the seventeenth-century Florentine Francesco Redi, physician to the Medicis. Redi had become curious about where the maggots that consume corpses come from. Were they generated spontaneously from rotting flesh, or did they arrive from elsewhere? He left some meat exposed and other pieces under muslin. The screened meat did not become maggot-infested, indicating to Redi that the flies that swarmed over the uncovered meat had produced the maggots. Redi carried out this remarkably modern-sounding controlled experiment not in the spirit of science, but out of strict adherence to Creationist principles.
Bereshit—In the beginning—the great book rings out as it commences the story of the seven days of creation. Redi fervently believed the story, as do millions of Christians, Jews, and Muslims today. To them spontaneous generation of life after that seventh day is heretical.
Before humanity could inquire into the origins of life in a wholly secular way, a complete revolution in the way people thought about their place in the world had to occur. The critical moment in that revolution came in 1859 when Darwin published The Origin of Species. Yet even Darwin believed that “in the beginning” life was “breathed by the Creator into a few forms or into one” and that evolution via natural selection came later.
Before long, however, belief in the initiating role of a divine creator waned, and for nearly a century the majority of Darwinian thinkers inhabited a world where there was no one “in the beginning.” Life, they believed, arose in the distant past as a result of the interaction of organic chemicals in an ocean of “primordial soup.” Yet ideas about precisely how life might have arisen remained vague, largely because no experimental work was carried out. The reason for this is not discussed by Wills and Bada, but if Shelley’s Frankenstein speaks for the age, then perhaps some residual reverence for the divine prerogative in creation was responsible.
A major advance was made in 1953, when Stanley Lloyd Miller—a twenty-three-year-old second-year graduate student in the Department of Chemistry at the University of Chicago—decided to grasp the rudder of this directionless debate. He would attempt to be there, in the beginning, as the creator of life or its precursors, albeit in a flask.
What Miller did was relatively simple: he mixed methane, ammonia, hydrogen, and water vapor in a sealed glass flask, then sent electric sparks through the mixture. In doing so he created some of the basic building blocks of life—the amino acids that are found in proteins. His first experiment resulted in the creation of a small amount of glycine, the simplest amino acid. Later he was able to synthesize thirty-three different amino acids, including over half of the twenty found in proteins.
The reason Miller mixed the chemicals he did, then passed an electric charge through them, lay in his understanding of what the Earth might have been like when life arose. Now we know much more about that world of four billion years ago—enough to see the limitations of Miller’s work—and to cause us to marvel at the way life has changed planet Earth.
No rocks survive from that ancient time before life, but tiny zircon crystals found embedded in younger rocks in Canada and at a place called Mount Narryier in western Australia do. Mount Narryier is a forbidding place—a weathered brown knob of a hill standing over an endless sea of sand, where life is reduced to a few spiny shrubs and bizarre, rock-imitating lizards.
The Spark of Life takes us on an imaginary stroll along a beach that must have existed somewhere near Mount Narryier four billion years ago, and then the region was even more hostile. In order not to die upon inhaling your first breath, its authors warn us,
you must wear a space suit, for there is no oxygen in the atmosphere. And the suit will have to be Teflon coated, because nasty gases present in the thick air, such as hydrogen sulfide and the vapors of sulphuric and hydrochloric acids, would certainly kill you very quickly by eating through any protective suit made of ordinary chemicals.
Can you see your surroundings? Not very well—the atmosphere is so smoggy that little or no light can penetrate to the surface, even at high noon. But lightning flashes do give you brief, lurid glimpses of your immediate neighborhood. And you might be able to see the red glow of a nearby active volcano.
A vast ocean stretches away into the darkness and murk. During the brief lightning flashes, you can see that it is covered by lumps of oily material. The color of the water between the lumps is a muddy reddish brown, stained by large quantities of organic substances. Great waves crash on the shore, built up unimpeded to awesome size as they cross the vast stretches of ocean that girdle the planet. As they break, strong winds whip the sea up into a roiling mass of foam. Gusts of rain slash across the landscape.
Winds and tides together have produced the huge, sandy intertidal zone across which you are trudging.
This was a dynamic landscape indeed, a dynamism clearly absent from Miller’s tranquil experiment in a bottle. Wills and Bada see the tide as the most important life-creating force acting on this world, and the tide was then formidable. The moon, newly wrenched from the earth by the impact of a Mars-sized planet, was much closer than at present. Casting a huge shadow across the planet’s face, its pull was such that even the Earth’s crust (which was then less rigid) rose and fell an extraordinary sixty meters twice each day. Wills and Bada do not give an example of the amplitude of the tide at that time, but it must have been truly awesome.
The tides are important to Wills and Bada’s argument both because they are regular and because they possess enormous potential to sort matter. One of the great stumbling blocks to understanding how life might have arisen is the necessarily dilute nature of amino acids in the ancient seas. Unless these building blocks could somehow be concentrated and separated from the chemical chaos surrounding them, there was little prospect that they could interact to create more complex molecules.
Wills and Bada have developed a model that overcomes this difficulty, which they dub “an ancient laboratory on a beach.” As you can see on any beach, tides sort out matter. Here you find a line or cluster of shells, there a line of finer or coarser sand. A beach, with its varying layers of silica and calcium carbonate fragments of differing size and shape, can act as a filter. When that filter is powered by a tide sweeping it twice each day, a beach has the capacity to sort molecules according to size and weight in a highly efficient manner. This process of separating molecules by size and weight is called chromatography—so named because it was first used in the laboratory to separate colored dyes.
Wills and Bada envisage their ancient laboratory on a beach as producing a constantly sifted chemical array. When they reached certain levels in the sand, organic chemicals would become concentrated. Tides might remove some, which the authors envisage as having “died,” while new ones would be washed in and become fixed, thus having been “born” into the chemical community that would ultimately form life. “The result,” they say, “would have been layers of organic molecules that would be constantly growing and changing, increasing in thickness and complexity.” Eventually “the mixture…acquired a definite structure that had been shaped by the ‘birth’ and ‘death’ process” wrought by chromatography and subsequent internal modification.
Here, Wills and Bada controversially claim to have discerned a sort of “proto-Darwinism,” which they nickname “Darwin Lite.” They metaphorically place Darwin where the great biologist himself saw only God at work, writing, “It is Darwin who sped up the origin of life from the primordial soup…and it is Darwin who will aid our efforts to duplicate those events in the laboratory.” If they are correct, then Darwin’s great engine of change partly explains the nonliving as well as the living worlds. This is a major extension of the concept of natural selection, and their argument will doubtless promote a vigorous debate among scientists, most of whom dispute that natural selection can occur in the absence of reproduction, inheritance, or anything that could be called metabolism.