Excerpts
Evolutionary Wars: A Three-Billion-Year Arms Race
The battle of species on land, at sea and in the air
Charles Kingsley Levy


  The Origins of Earth
About 4 1/2 billion years ago a ball of cosmic debris came together to form earth, some 93 million miles from the Sun.  From this distance the Earth is considered in the liquid water zone, far enough so the water won’t boil yet close enough that the water won’t freeze solid.

In it’s infancy Earth was a molten ball heated by the energy released in the decay of radioactive material and meteor impacts.  As it cooled Earth divided into layers.  The inner and outer molten cores made up of heavy metals, iron and nickel.  The lower mantle (1,700 miles thick); the upper mantle (400 miles thick); and the outermost layer, the rocky crust (6-25 miles thick).  Gases expelled in the process of formation created a primitive atmosphere nearly devoid of oxygen.

Earth’s crust, composed of the lightest materials, literally floats on the more dense lower layers of the mantle, which circulate, driven by heat released from the core.  The surfaces that make up the continents are driven by this motion, moving as vast plates in a gigantic recycling engine; new hot materials push up from below, while at the margins, old crusts cool.  When the moving plates collide, the cooler material is pushed back into the core; in areas called subduction zones.  So, the crust is constantly being created and destroyed.  The movement of the plates is slow.  For example, India and Australia, pushed apart by hot plumes rising from the mantle, split off from the Antarctic plates; causing a massive buckling up that formed the Himalayan Mountains.  (In fact, India is still moving northward into Asia and the Himalayas are still growing.)

Over time, the constant movement of plates formed super continents, which rifted apart and came together and rifted apart again to form the present continents.  During the past 650 million years, continental drift spawned monumental changes in Earth's atmospheric temperature.  There was alternating hot and cold periods, during which huge ice caps formed and melted, and ocean levels fell and rose.  The rifts in the crust also led to immense volcanic eruptions which had dramatic effects on Earth's environment.  In all probability, these eruptions played a major role in some of the great extinction's of life on Earth.

 The Nature and Origins of Life
Ever since the human species became aware of itself, it had been concerned with its nature and origins.  Indeed, as one studies the fossil records of our early ancestors and the myths of Stone Age people, evidence of our ancestors’ interest in their own nature can be seen as a measure of their progress toward humanness.  Their early speculations led them to realize that they were part of a large group of Earth dwelling objects that were alive; so, their first attempts to understand the world probably involved the separation of living objects from nonliving objects.  Once they recognized differences between animate and inanimate objects, humans developed an interest in the nature of life itself and how it began.  

Only in this century, and particularly in the last 50 years, however, have we acquired enough understanding of chemistry, physic, and astronomy to replace mystical speculation with more precisely defined concepts of chemical reactions, molecular structure, molecular interactions, and a variety of biophysical events.

With our expanded knowledge about the chemistry of life and our increased understanding of information coding at the molecular level, we have been able to create scientifically sound theories about how life evolved from non life, what produced diversity, and how more advanced forms of living things evolved.  Not only are we able to create theories; we are also able to devise laboratory experiments to test some of these theories.  A number of these experiments have demonstrated successfully that the constituents of the primeval nonliving Earth could, under proper conditions, be converted into more complex combinations of atoms that are similar or identical to molecules found in living organisms.

    What Is a Living organism?
Living is a very difficult adjective to define.  Any attempt to define life must be somewhat subjective and arbitrary.  But we humans are very arbitrary beings; we love to make long lists of what is acceptable as a condition for life (and almost anything else).  Still while we like sharp clear cut separations of living from nonliving, we are rational enough to realize that over the vast reaches of time, there was undoubtedly a gradual transition from what is clearly nonliving to something that may be living to something that is clearly alive.  Simply to avoid argument, Nobel laureate Melvin Calvin came up with two qualities that everyone could agree on as basic characteristics of a living system.  These were : 

(1) "the ability to transfer energy and transform energy in a directed way "
and
(2) "the ability to remember how to do this, once having learned it, and to transfer, or communicate, that information to another system like itself which it can reconstruct".

What do these two qualities mean?  The ability to transfer and transform energy signifies that living things are able to convert chemical and physical energy into energy that is useful to themselves, photosynthesizing sunlight, for example, or using food to fuel their bodies.  The sum total of chemical reactions that either build new molecules or break down existing molecules to transform their chemical energies is referred to as metabolism.  All living things are capable of metabolism.  The communication of information implies that living things are responsive to their environment and can reproduce their own kind.  in other words, living organisms have the capacity to use their information containing molecules, not only to produce similar organisms but also to program the functioning of those organisms within their environment.

Salvador Luria, also the winner of a Nobel Prize, points out that living is distinct from all other natural events in that it has a program, whereas physical phenomena are essentially random events tending toward increasing disorder.  Life not only manifests individuality but also in a complexity maintains order not otherwise seen in the physical world.

   The Program for Life
The material that contains the blueprint for life, the programming substance that has persisted in a variety of forms for over 3.5 billion years, is the gene.  The gene is a molecule whose very construction ensures stability and thereby, continuity in the general features of any species or plant or animal group.  At the same time, the structure of the gene can be altered to produce a vast variety of specific changes, changes that permit evolution to take place.  So, another characteristic of life is its ability to evolve.

Evolution is not seen in the physical world.  Crystals reproduce, but this repetitious process always produces identical crystals.  In contrast, because living things are capable of change, they have produced diversity unheard of in the nonliving world.  But somehow life must have begun as a chemical, that is , a physical phenomenon; life must somehow have arisen from nonliving components.  While we have no direct evidence about how and where the first gene like, self replicating molecules appeared, we can speculate about how they came to be.

 Vulcanism and Earthquakes
As heat, escaping from the mantle, rises in thin "roots," it reaches the bottom of Earth's crust and spreads out, forming a dome of hot molten rock, or magna, lifting the crust, and red hot molten lava flows out over the surface.  In the course of human history, we have recorded a number of large, catastrophic volcanic eruptions and severe earthquakes caused by plate movements, but these pale in comparison to the incredibly violent events of the past.  

About 250 million years ago, a time period that coincides with the mass extinction at the start of the Paleozoic period, a series of massive eruptions occurred in what is now Siberia.  A gigantic flood of lava, over 700 miles of it, poured out, and vast quantities of dust, droplets of sulfur dioxide, and other gases were blasted into the atmosphere.  These substances spread out over Earth's entire surface and caused both short term an long term effects on its environment.  The largest volcanic eruption of recent history, which occurred in 1815 on the island of Tamboura, in the East Indies, pumped enough ash and gas into the air to diminish the amount of sunlight hitting Earth's surface as lower temperatures.  This effect was substantial enough that in Europe it was called the year without a summer.  

During the eruptions in Siberia and later massive volcanic eruptions in India, mind boggling quantities of material were injected into the atmosphere: trillions of tons of carbon dioxide, trillions of tons of sulfur, billions of tons of flourine and chlorine, and untold amounts of volcanic ash.  The first effect was the shield the earth from sunlight an cause the death of many photosynthetic organisms, organisms that normally sop up carbon dioxide (CO2).  Earth's temperatures dropped rapidly, by as much as 10 degrees F.  Sulfur dioxide reacting with water vapor produced clouds of acid, which subsequently fell to Earth's' surface, acidifying the seas and killing oceanic photosynthesizes.  Still loaded with CO2 and other gases, the atmosphere later reflected heat rising from the surface back toward Earth, a process similar to what happens in a glass green house.  As a consequence, average global temperatures subsequently rose as much as 10 degrees F.

Along with the rifts and fractures of the crusts, there were earthquakes of staggering proportions, some so severe that they would reach 13 or 14 on the Richter scale, 1 million to 10 million times greater in magnitude than anything in recorded history.  The cataclysmic eruptions and devastating earthquakes that occurred in or near the oceans caused tidal waves, or tsunamis, that sent walls of water over 200 feet high smashing inland over low lying coastal environments.  Certainly, such physical changes on Earth can account for some of the mass extinction's that occurred in the past 600 million years.  But there is another form of severe physical disruption that could cause even greater effects;  the impact of some reasonably large extraterrestrial body ( and asteroid or comet) on Earth.

  The Extraterrestrial Impacts
From the very beginning, Earth has been bombarded by extraterrestrial objects; comets, asteroids, and meteorites.  Just a quick glance at our moon through a small telescope reveals a massively pockmarked surface, covered with large and small impact craters.  On Earth itself, we find scars left by large extraterrestrial objects that passed through our atmosphere without burning up and smacked into Earth with devastating force.  A large meteorite hit Arizona just 3,500 years ago and created a bowl shaped crater almost a mile across.  Even as recently as 1908, a comet or meteorite a few hundred feet in diameter exploded over Siberia, leveling every tree in over a thousand square miles.  The object, traveling at about 35,000 MPH on impact, generated local temperatures of about 30,000 degreed F.  What would the effect be on even larger extraterrestrial impacts on Earth's environment?

Recently, evidence of another large impact, also in what is now Siberia, has been dated at 35.5 millions years ago.  The extraterrestrial object left a crater, known as the Popogai structure, 100 kilometers in diameter.  The time frame of this impact, at the boundary of the Eocene and Oligocene periods, coincides with the most severe extinction since the demise of the dinosaurs.  We can correlate this impact with the cooling of the oceans and the appearance of ice sheets over Antarctica.  At about the same time, another impact left and 85 kilometer wide crater in the area of the Chesapeake Bay on the east coast of North America.  Thus, two successive cataclysmic impacts are implicated in the mass extinction's of the Eocene Oligocene boundary.

Recently, the site of the impact of a mile wide asteroid in western Argentina has been uncovered by a team of scientists led by Peter Schultz of Brown University and Marcello Zarate of Argentina.  The crater is thought to be off the coast and has yet to be located.  But glass fragments created by the heat of the impact are rich in iridium, a mineral rare on Earth but common in asteroids.  Sediment cores of the nearby seafloor show that there was a sudden drop in temperature about 3.3 million years ago that lasted about 50,000 years, possibly triggering the beginning of an ice age.  It has been suggested that this impact was responsible for the demise of the giant marsupial ground sloths; the monstrous armored armadillos; the 8-10 foot tall, flightless, carnivorous terror birds; and other huge mammals that become extinct after that species killing impact.

Most of us have read somewhere in the popular press about a similar event that occurred about 65 million years ago and wiped out the dinosaurs.  There is now overwhelming evidence that an asteroid, 6-9 miles across, weighing a trillion tons, and traveling at a speed of about 150,000 MPH, smashed into Earth on the Yucatan Peninsula.  The impact created a crater about 30 miles deep and 90 miles in diameter.  The explosion injected such a mass of dust and water vapor into the upper atmosphere that no sunlight penetrated it for a number of years.  The heat of the impact and hot, falling debris started massive forest fires.  In the area of the impact the intense hear caused atmospheric water to react with nitrogen and oxygen to make nitric acid, which then precipitated out.  The precipitation of the acid changed the acidity of the oceans and killed most species of aquatic microorganisms.  Later, because of  the lack of sunlight, Earth's land surface temperatures fell to below freezing.  Later still, the accumulated atmospheric carbon dioxide increased fivefold, producing a green house effect, raising global temperatures more than 10 degrees F, disrupting food chains, producing cataclysmic climate changes, and annihilating more than 50% of the species of plants and animals then dwelling on Earth, including dinosaurs.

Relating to mass extinction's revealed by geological studies to catastrophic impacts or episodes of monstrous vulcanism is difficult, and controversy rages between the proponents of different theories. We have compelling evidence of six great extinction's and several smaller ones that occurred from the Cambrian period up to the modern era.  Thanks to great technological advances in radioactive dating of rocks and sediments, the time of these cataclysmic events is fairly well pinpointed, but the exact cause or causes of the massive annihilations are still matter of very heated debate.  The details of this debate are clearly presented in a very readable fashion by Lowell Dingus and Timothy Rowe in their elegant book, The Mistaken Extinction, Dinosaur Evolution and the Origin of Birds (New York: Freeman, 1998).  However, the evidence for the cause of the mass extinction at the end of the Cretaceous period overwhelmingly points to an impact by a very large asteroid 65 million years ago.

Although each extinction killed off varying numbers of plant and animals species, it also left survivors to fill the ever-changing niches created.  These survivors multiplied, evolved, diversified, and took over.

  The Bizarre Creatures of the Cambrian Big Bang
The cause of the Cambrian big bang is unknown.  Most evolutionary biologists think it was related to some pervasive change in the environment of that time, possibly an increase in atmospheric oxygen.  What is clear is that it led to an arms race in which predators and prey developed the elaborate weaponry and sophisticated strategies and tactics that are carried on by their descendants today.  The suddenness of the appearance of these animals with eyes, tentacles, claws, jaws, spines, and armor is unprecedented in the history of life.  It all happened in a span of about 10 million years, a mere blink in the evolutionary course of time.  

Fossils found on the 530 million year old Burgess Shale reveal that in the relatively short span of a few million years, an enormous number of new and bizarre life forms appeared-an evolutionary big bang of sorts.  

The remnants of the big bang, many long vanished from the planet, are engraved in slices of shale excavated from geological formations in the Canadian Rockies (the famous Burgess Shale) and China.  There were worm like ambush hunters that burrowed into the seabed floor capable of extruding a thorny proboscis to snag their prey.  There were arthropods that had sensory antennae and eyes on stalks; some had spine-tipped appendages, while still others had clawed legs.  There were flexible plates of armor and defensive spines.  Many were predators that preyed on the abundance of simpler multi cellular organisms that preceded them.  Some, such as Opabinia, had five eyes; segments covered with armor; and a long, flexible proboscis with clasping jaws.  They were like creatures out of science fiction.  One, so bizarre that it seemed to be the product of an hallucination, was promptly classified Hallucigenia.  

 Mass Extinction’s and Radiation’s
Examining the 500 million-year history of complex multi cellular animals reveals six massive extinctions.  While the cause of most of these extinction’s is not clear, we do know that each was followed by a radiation of surviving life forms.  Such radiations give rise to new variations, which eventually become diverse new species.  

One of the most dramatic of these radiation’s took place between 440 and 510 million years ago on the warm, sunny tropical seas.  Called the Ordovician radiation, it produced organisms that would dominate all the oceanic ecological niches for 250 million years.  But the Ordovician radiation is unusual in that it was not proceeded by a major extinction.  The more usual course of radiation’s is that they follow a cataclysmic event, and the survivors of the dramatic change then exploits the opportunities made open to them by the demise of previously dominant species.  This was how, after the great extinction of flying and marine reptiles and of the dinosaurs, the birds and mammals rose to ascendancy.  For example, accumulated recent evidence for the demise of the dinosaurs, many marine species, and all of the ammonite mollusks, about 65 million years ago, points to a massive meteor impacting the earth in an area near the Yucatan Peninsula.  Whether other extinctions were caused by extraterrestrial bodies hitting the earth, by volcanism, or by combination of both remains unknown.  

  The Fire Ants
Fire ants of the genus Solenopsis, though tiny, are among the most insatiable, aggressive, and terribly fecund ant species.  They live in huge underground super colonies, which may house more than 500 queens.  Each of the millions of workers is equipped with strong pincer like mandibles and a potent stinger, a needle sharp, barbless hypodermic, thought which poison is injected.  Introduced into the US in 1918, fire ants have spread with astounding swiftness throughout most of the southern states.  They have infested over 25 million acres, and a single acre can be home to more than 20 million ants, or about 500 individuals per square foot.  Fire ants send hordes of foragers to search for food, which is ingested and then carried back to the nest, where it is regurgitated to feed their nest bound, hungry cohorts.  Guidance back to the nest, which may be more than 100 feet away, is achieved by trail marking pheromones.  There is some evidence suggesting that these ants are also capable of solar or lunar navigation.

Once they latch onto a prey or intruder, they can sting repeatedly with their barbless stingers.  Their venom is a lot less toxic than that of some other ants, such as the Costa Rican ant called “bullet” (because when it stings, you feel as if you’d been shot), or the giant red Australian bulldog ant, whose sting is so toxic that 30 stings can kill an adult human.  However, despite the mild toxicity of their venom, the fire ants are so numerous and so aggressive that they can deliver thousands of stings to an intruder.  It has been estimated that 5 million people per year have been stung by them and that 40,000 to 60.000 of these victims required visits to the emergency room.  Despite massive efforts to control them by using the most advanced technology, humans have been unable to deter their unrelenting advance.  Chalk one of for the ants.

 The Arrival of the Reptiles
Reptiles (meaning crawlers) evolved from some ancestral amphibians about 340 million years ago.  These small, lizard like pioneers of land were the first vertebrates equipped to fully exploit terrestrial life.  Their tough, scaly skin could resist drying out, and their eggs had hard-mineralized shells that resisted desiccation.  In the subsequent diversification of reptilian types, the ancestors of dinosaurs, birds, and even mammals had their humble beginnings.  About 248 million years ago, some sort of cataclysmic event caused mass extinction’s of about 70% of the species.  Afterward, the reptilian survivors quickly diversified, multiplied, and took over the planet in the Mesozoic era.  The Mesozoic era, which lasted some 155 million years, is also called the Age of Dinosaurs.  It was divided into three periods, the Triassic, the Jurassic, and the Cretaceous.  

Many of the new reptiles stood upright and walked and ran in a manner unlike the sprawling gait of their crocodile like ancestors.  This new improved gait, with knees tucked in directly below the body, required the evolution of major changes in the bones of the hips, shoulders, forelimbs, hind limbs, and feet as well as the development of hinges like ankles and wrists.  With these changes dawned the Age of the Dinosaurs, the Triassic period (248 to 213 million years ago.)  The landmass at that time was a giant super continent, now referred to as Pangea, but great plates of the earth’s crust were on the move and the landmass was already beginning to split in two.  The climate was warm and moist along the coasts, where moisture loving ferns, horsetails, and treelike cycads provided sustenance for herbivores, while the inner , rainless portions were vast deserts.  Most of the reptiles of this Triassic period were small, although there were a few larger plant eaters.  There were small mammal like reptiles that gave rise to the tiny shrew like prototherians, the ancestral mammals.  There were also ancestors of the birds and ruling dinosaurs’ that evolved in the Jurassic period (213 to 144 million years ago).  

During the Jurassic period, the continents were drifting apart.  Old mountains were wearing down, and shallow seas invaded much of the landmass, bring rain to former deserts.  The warm climates promoted diversification and growth, including the appearance of a number of enormous herbivores and predators. By the beginning of the Cretaceous period (Creta in Latin for “chalk”), the continents had almost reached their present positions, although what is India today was still an island on the move.  The climates had seasonal, and an enormous variety of flowers, plants and trees covered the land’s surface.  The Cretaceous period (144 to 165 million years ago), the longest part of the Age of the Dinosaurs, came to an end at the Cretaceous Tertiary boundary when a massive extraterrestrial body impacted the earth in the region of the Yucatan and wiped out the vast majority of species.  But during their protracted reign, the dinosaurs had already established the strategies and tactics for the arms race to follow.  

  The Solitary Cats
Today there are about 37 known wild species of cats.  They range in size from the typical domestic cat to the true king of the cat family, the Siberian tiger.  These huge felids should not be confused with the prehistoric Sabre toothed tigers, since they represent a totally different branch in the evolution of cats.  The Sabre toothed cats were contemporaries of early humans.  With their enormously long canine teeth, they prayed on large, thick skinned herbivores like the wooly mammoths and became extinct less than a million years ago.  Modern tigers, to the best of our knowledge, evolved from a stem of ancestor in South China slightly more than 2 million years ago.  These cats radiated over much of Asia, some as far eastward as the Caspian Sea.  They were initially classified as Felis tigris, but subsequent anatomical studies revealed that tigers and their cousins, the lions, the leopards, and the jaguars, had elastic bony supports for their tongue, so, they were reclassified into the genus Panthera.  The combination of these elastic bones and the peculiar structure of their vocal apparatus (larynx) acts like a slide trombone to produce the deep roars that carry over long distances.  These same structures also allow them to purr when exhaling, while the smaller cats purr during both inhalation and exhalation.  

  The First of Many
The earliest parasites were in all probability viruses that prayed on ancestral bacteria.  While we have no fossil record to justify this assumption, it seems reasonable.  Modern day bacterial parasites, the so called bacteriophages, can serve as a model.  There are many known species of bacteriophage viruses.  They look like miniature luna landers, having a hexagonal shaped head which consists of a protein envelope filled with viral hereditary material, a collar, a tubelike penetrator, and an array of long, leg like structures.  The tips of these legs bear recognition proteins that are highly specific for molecules of bacterial surfaces.  Once the phage has landed and is locked in place on the bacterium, the penetrator is driven in and, like a hypodermic needle, it injects the viral genetic program into the bacterium.  Inside of the bacterium, the viral genetic program takes over.  Using the host's metabolic machinery, the phage begins to manufacture new viral materials, which in turn are assembled into new bacteriophages.  In some cases, the host releases the new bacteria over a protracted period of time.  In some cases, the host bacterium, filled with newly constructed phage, ruptures, releasing a horde of new, infective phage particles.  

 The Flatworms
About 1 billion years ago, one of the earliest groups of multicelled organisms to appear was the relatively simple creature that lacked a body cavity and had no mechanism for transporting oxygen to its inner tissues.  This being the case, evolution dictated a body plan in which all cells had to be near a surface that could supply oxygen, in other words, a flattened body form.  These animals, the platyhelminthes, flatworms' early ancestors, were free living marine and fresh water organisms that fed on debris and carrion.  However, the flat basic body plan easily led to a parasitic way of life.  Some evolved as external parasites, and some as internal parasites of vertebrates.  Today, there are over 25,000 species of known flatworms.  Many of them are parasites that afflict humans.  The parasitic flatworms can be broken down into two groups: the trematodes, or flukes, and the cestodes, or tapeworms.  no group of parasites demonstrates the essence of the parasitic way better than the teratodes.

06/05/03