that life could
not
have begun with DNA. DNA cannot survive by itself; it cannot function at all except in dialogue with cytoplasm and all that goes on in it. Furthermore, the DNA molecule is itself extremely intricate and highly evolved. It could not have been the first on the scene. RNA is simpler and can make a better fist of independent living—but RNA, too, is a highly evolved molecule. DNA and RNA were not the prime movers, therefore. We might as soon say that by the time these two aristocrats had come on board, the hard work had already been done. At least, the absolute beginnings had been left far behind.
In truth, the essence of life is metabolism—the interplay of different molecules to form a series of self-renewing chemical feedback loops that go around and around and around. And they do this simply because, chemistry being what it is, such a modus operandi is chemically possible, and what is possible sometimes happens. The first life, so it is widely argued, was simply a metabolizing slime that spread over the surface of the earth, which in those early days was a very different place from now. Indeed, it was a nightmare world, at least by our standards: hot, steamy, volcanic, with an atmosphere absolutely devoid of oxygen and probably full of gases such as ammonia and hydrogen cyanide that would snuff out almost all life of the kind we know today in a trice. The hot springs of present-day Yellowstone, New Zealand, and Iceland and the perpetually outgassing vents in the depths of the great oceans give some idea of what that early world was like. An extraordinary variety of creatures live within today’s hot springs—most of which would be poisoned by oxygen if they were ever exposed to it. Anthropocentrically, we think of ourselves as “normal” and call the creatures of the hot springs “thermophiles”—heat lovers. But historically speaking, they are the normal ones.
We—
human beings and dogs and oak trees—are the highly evolved anomalies: the cold-loving “aerobes,” utterly dependent on the hyperreactive gas—oxygen—that would have laid our earliest ancestors flat.
TRANSFORMATION 2: ORGANISMS
Life today is not a continuous slime. For at least three billion years the substance of life has been divided into discrete (or fairly discrete) units, each known as an “organism.” Of course, we don’t know how, in practice, this separation came about—and never can, until someone builds a time machine. But we can speculate.
For natural selection would have been at work within the original slime, just as it is today and always has been. Inevitably, some bits of the slime would have metabolized more efficiently than others. Some of the endlessly cycling chemical feedback loops would have harnessed energy and processed raw materials more rapidly than others. The bits that worked best would have been held back by the bits that worked less well. Natural selection would surely have favored the bits that were not only more efficient but also cut themselves free from the rest, surrounding themselves with membranes to monitor and filter all inputs from the world at large.
So the first organisms came about: the first discrete creatures. After a time (probably a long time) these primordial creatures developed the general kind of structure that is still seen in present-day bacteria and archaea (pronounced
ar-key-uh—
creatures with a similar general form to bacteria which in fact have a quite different chemistry). We tend to say that bacteria are “simple,” not least because they are small. In truth, of course, nature is far more wondrous than anything we could cook up and bacteria in reality are more complex than battleships, and a great deal more versatile.
TRANSFORMATION 3: MODERN-STYLE CELLS
Compared with us (or indeed with mushrooms or seaweeds or flowering plants), bacteria
are
simple. In particular, they keep their DNA loosely packaged, hanging around the cell. In our own body cells (and
not
have begun with DNA. DNA cannot survive by itself; it cannot function at all except in dialogue with cytoplasm and all that goes on in it. Furthermore, the DNA molecule is itself extremely intricate and highly evolved. It could not have been the first on the scene. RNA is simpler and can make a better fist of independent living—but RNA, too, is a highly evolved molecule. DNA and RNA were not the prime movers, therefore. We might as soon say that by the time these two aristocrats had come on board, the hard work had already been done. At least, the absolute beginnings had been left far behind.
In truth, the essence of life is metabolism—the interplay of different molecules to form a series of self-renewing chemical feedback loops that go around and around and around. And they do this simply because, chemistry being what it is, such a modus operandi is chemically possible, and what is possible sometimes happens. The first life, so it is widely argued, was simply a metabolizing slime that spread over the surface of the earth, which in those early days was a very different place from now. Indeed, it was a nightmare world, at least by our standards: hot, steamy, volcanic, with an atmosphere absolutely devoid of oxygen and probably full of gases such as ammonia and hydrogen cyanide that would snuff out almost all life of the kind we know today in a trice. The hot springs of present-day Yellowstone, New Zealand, and Iceland and the perpetually outgassing vents in the depths of the great oceans give some idea of what that early world was like. An extraordinary variety of creatures live within today’s hot springs—most of which would be poisoned by oxygen if they were ever exposed to it. Anthropocentrically, we think of ourselves as “normal” and call the creatures of the hot springs “thermophiles”—heat lovers. But historically speaking, they are the normal ones.
We—
human beings and dogs and oak trees—are the highly evolved anomalies: the cold-loving “aerobes,” utterly dependent on the hyperreactive gas—oxygen—that would have laid our earliest ancestors flat.
TRANSFORMATION 2: ORGANISMS
Life today is not a continuous slime. For at least three billion years the substance of life has been divided into discrete (or fairly discrete) units, each known as an “organism.” Of course, we don’t know how, in practice, this separation came about—and never can, until someone builds a time machine. But we can speculate.
For natural selection would have been at work within the original slime, just as it is today and always has been. Inevitably, some bits of the slime would have metabolized more efficiently than others. Some of the endlessly cycling chemical feedback loops would have harnessed energy and processed raw materials more rapidly than others. The bits that worked best would have been held back by the bits that worked less well. Natural selection would surely have favored the bits that were not only more efficient but also cut themselves free from the rest, surrounding themselves with membranes to monitor and filter all inputs from the world at large.
So the first organisms came about: the first discrete creatures. After a time (probably a long time) these primordial creatures developed the general kind of structure that is still seen in present-day bacteria and archaea (pronounced
ar-key-uh—
creatures with a similar general form to bacteria which in fact have a quite different chemistry). We tend to say that bacteria are “simple,” not least because they are small. In truth, of course, nature is far more wondrous than anything we could cook up and bacteria in reality are more complex than battleships, and a great deal more versatile.
TRANSFORMATION 3: MODERN-STYLE CELLS
Compared with us (or indeed with mushrooms or seaweeds or flowering plants), bacteria
are
simple. In particular, they keep their DNA loosely packaged, hanging around the cell. In our own body cells (and
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