those of mushrooms, seaweeds, and flowering plants) the DNA is neatly contained and cosseted within a discrete nucleus, cocooned in its discriminating membrane. Cells of this modern kind are said to be “eukaryotic” (Greek for “good kernel”). The nucleus is surrounded by cytoplasm, and within the cytoplasm there is a series of bodies known as “organelles” that carry out the essential functions of the cell. Among these organelles are “mitochondria,” which contain the enzymes responsible for much of the cell’s respiration (the generation of energy). These are found in all eukaryotic cells (apart from a few weird single-celled organisms that live as parasites, but they belong in another book). Plant and other green cells contain a unique kind of organelle known as the “chloroplast.” This contains the green pigment chlorophyll, which mediates the process of photosynthesis.
I am treating all this in some detail because herein lies a tale of immense importance, which is crucial to all ecology, and is discussed again in Chapter 13. For the eukaryotic cell evolved as a coalition of bacteria and archaea. Broadly speaking, the cytoplasm seems to have originated as an archae. Either this ancient archae then engulfed some of the bacteria around it or the bacteria invaded it—or both. In any case, some of those engulfed or invading bacteria became permanent residents—and evolved into the present-day organelles. Mitochondria and chloroplasts both contain DNA of their own. The DNA of mitochondria most closely resembles that of present-day bacteria of the kind known as proteobacteria. The DNA of chloroplasts resembles that of the bacteria that still manifest as cyanobacteria (in the past erroneously called “blue-green algae”). Cyanobacteria, not plants, were the inventors of photosynthesis.
In his notion of evolution by means of natural selection, Darwin emphasized the role of competition. Soon after Darwin published
The Origin of Species,
the philosopher and polymath Herbert Spencer summarized natural selection as “the survival of the fittest,” which was taken by post-Darwinians to imply that evolution proceeds by the stronger treading on the weaker. Two decades before Darwin, Lord Tennyson wrote of “nature red in tooth and claw”; and “Darwinism,” extended backward to embrace Tennyson and forward to Spencer, is commonly perceived these days as an exercise in the strong bashing the weak. But Darwin stressed, too, that we also see collaboration in nature; he made a particular study of the long-tongued moths that alone are able to pollinate deep-flowered orchids: two entirely different creatures, absolutely dependent on each other.
Yet we see a far more spectacular illustration of nature’s collaborativeness within the fabric of the eukaryotic cell itself—the very structures of which we ourselves are compounded. For the eukaryotic cell is a coalition. It was formed initially by a combination of several different bacteria and archaea that hitherto had led separate lives (and others are probably involved, besides the proteobacteria and cyanobacteria). Over the past two billion or so years the eukaryotic cell, innately cooperative, has proved to be one of nature’s most successful and versatile creations. There could be no clearer demonstration that cooperation is at least as much a part of nature’s order as is competition. They are two sides of a coin.
The ancestors of today’s plants arose from the ranks of the general melee of eukaryotic cells. These first ancestors contained chloroplasts and were green, and these can properly be called “green algae.” Many single-celled green algae are still with us (they often turn ponds bright green).
It’s a reasonable guess that the first green algae appeared on earth about a billion years ago. Thus it took about 2.5 billion years to get from the first living things to single-celled green algae, and only another one billion to get from single-celled
I am treating all this in some detail because herein lies a tale of immense importance, which is crucial to all ecology, and is discussed again in Chapter 13. For the eukaryotic cell evolved as a coalition of bacteria and archaea. Broadly speaking, the cytoplasm seems to have originated as an archae. Either this ancient archae then engulfed some of the bacteria around it or the bacteria invaded it—or both. In any case, some of those engulfed or invading bacteria became permanent residents—and evolved into the present-day organelles. Mitochondria and chloroplasts both contain DNA of their own. The DNA of mitochondria most closely resembles that of present-day bacteria of the kind known as proteobacteria. The DNA of chloroplasts resembles that of the bacteria that still manifest as cyanobacteria (in the past erroneously called “blue-green algae”). Cyanobacteria, not plants, were the inventors of photosynthesis.
In his notion of evolution by means of natural selection, Darwin emphasized the role of competition. Soon after Darwin published
The Origin of Species,
the philosopher and polymath Herbert Spencer summarized natural selection as “the survival of the fittest,” which was taken by post-Darwinians to imply that evolution proceeds by the stronger treading on the weaker. Two decades before Darwin, Lord Tennyson wrote of “nature red in tooth and claw”; and “Darwinism,” extended backward to embrace Tennyson and forward to Spencer, is commonly perceived these days as an exercise in the strong bashing the weak. But Darwin stressed, too, that we also see collaboration in nature; he made a particular study of the long-tongued moths that alone are able to pollinate deep-flowered orchids: two entirely different creatures, absolutely dependent on each other.
Yet we see a far more spectacular illustration of nature’s collaborativeness within the fabric of the eukaryotic cell itself—the very structures of which we ourselves are compounded. For the eukaryotic cell is a coalition. It was formed initially by a combination of several different bacteria and archaea that hitherto had led separate lives (and others are probably involved, besides the proteobacteria and cyanobacteria). Over the past two billion or so years the eukaryotic cell, innately cooperative, has proved to be one of nature’s most successful and versatile creations. There could be no clearer demonstration that cooperation is at least as much a part of nature’s order as is competition. They are two sides of a coin.
The ancestors of today’s plants arose from the ranks of the general melee of eukaryotic cells. These first ancestors contained chloroplasts and were green, and these can properly be called “green algae.” Many single-celled green algae are still with us (they often turn ponds bright green).
It’s a reasonable guess that the first green algae appeared on earth about a billion years ago. Thus it took about 2.5 billion years to get from the first living things to single-celled green algae, and only another one billion to get from single-celled
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