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Living Systems in Evolution

Elisabet Sahtouris

copyright © 1999 by Elisabet Sahtouris


From Polyps to Possums


One of the many remarkable things about life is its memory. The process of life creates and stores information -- not just the kind of information needed to reproduce each new body from a single tiny cell, but remembered information about much of its evolution over aeons of time. The way each of us came into being shows us something of the whole dance of evolution since the time of the first protists. Before we are even born -- in just a short nine months -- we repeat many steps in a billion years or so of our evolution as Earth creatures.

Each of us began as a single cell, much like an ancient protist that began its life by sexual reproduction, as the offspring of two parents. This new-creature cell divided again and again, cloning itself first into two cells, then into four, eight, sixteen, thirty-two, sixty-four cells, and so on until there was a simple ball-like creature very much like a protist colony. This creature in its early stages lived like other protist colonies in a salty sea -- a special uterine bag of salty liquid duplicating our real ancestral sea.

Our own embryonic colony of cells soon specialized and turned us into multicelled creatures. If you could watch a movie of your own development -- you may have seen films of human embryos developing -- you would see the ball-colony change shape as its specialized cells divide again and again. One side of the ball dents in to form a groove where the backbone will grow. A lumpy head appears at one end. Soon it looks like a tiny fish with gill slits; dark eyes bulging in its big pale head, and a tail that starts twitching. A little later it looks so much like the developing embryos of frogs and turtles, then chickens and pigs, that it is hard to say what it is going to become. Even when our arms and legs have budded from our bodies, we still look much like other animal embryos.

Slowly we continue our formation as we roll about comfortably in our warm sea. Our tails shrink to nothing, our brains grow bigger, our arms and legs and faces become human. Finally, after nine months, we leave our maternal sea to begin breathing air.

How fascinating that this memory of the Gaian life dance is relived by each of us, reminding us of just who we are, where we came from, how we are related to all other species and to the whole dance of life -- the evolutionary dance we traced at the end of the last chapter to our discontented polyp ancestors. Let's continue now to see what made them evolve into more complicated animals and how they came to leave their ancestral sea.

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Dull as the polyp's life cycle was at the beginning and end, the middle stages as medusa and planula permitted some adventure, some spreading into new environments. Somewhere along the line, certain young planulae seem to have felt their difference and rebelled against settling down and growing into a dull adult life as polyps. They began growing up straight into medusae, simply skipping the whole attached polyp stage. Others began sexually reproducing themselves as planulae, skipping even the medusa stage and evolving, generation by generation, into various species of wormlike and then fishlike creatures.

The evolution of new species from the baby stage of a parent species is known by evolutionists as neoteny -- meaning `stretched youth.' Neoteny is a kind of evolutionary step backwards in the dance when a species finds itself at some adult dead end or blind alley, when for some reason the body organization of the grown-up stage evolves to limits that get it stuck.

It seems that when a species becomes highly specialized for a particular and successful way of life, it loses variety in its DNA and ends up with a very fixed body structure that can no longer change or evolve. We can see such dead ends in polyps living today, or in sharks, which are still very like their ancient ancestors, having evolved no further. But in some ancient species, as we said, nature took advantage of the fact that baby planulae, which did not yet have the specialized bodies of adults, could still change. We can trace the descent of some free-swimming creatures back to ancestors who were very likely unspecialized planula babies. Later we will see that neoteny produced other interesting new species, including our own!

Among the new parts of the more complex bodies evolving from planula -- like ancestors were networks of nerves. These seem to have evolved from in-turned rowing cilia that became tubes for sending messages from cell to cell. Once animals evolved nervous systems they kept improving them and never gave them up, for these communications systems made it possible to organize ever greater numbers of cells within a single creature, just as nuclei had made it possible to organize ever greater numbers of cell parts within a protist.

Organizing now meant actually forming organs -- grouping cells into body parts specialized for particular jobs, such as guts for digesting food, hearts and blood vessels for circulating supplies, eye spots for telling light from dark and later making images that helped identify food or predators. Remember that animals were pushed to evolve complex organs because they had to hunt for their food rather than make it themselves. The other side of that coin is evolving ways to avoid being eaten yourself.

An extra tube, stiff but bendable, evolved along the main nerves running from one end of early wormlike animals to the other. This protected the delicate nerves against damage. Later the tube wrapped itself right around them to become a backbone. But long before that happened, the tube was useful in another way. Long cells, good at stretching and shrinking, attached themselves to it, pulling the tube into wavy patterns. That was the beginning of muscles, which gave creatures an important new way of moving themselves -- from the inside, rather than by outside rowing hairs or tails.

Clumps of nerves at the head end of creatures evolved into simple brains; the eye spots evolved into true eyes with lenses to focus light and retinas to make images of what went on in the environment. Squid and cuttlefish have bodies that remind us of tube-shaped polyps with tentacles, but they have evolved eyes not unlike our own. Lyall Watson pointed out the biological mystery of why such wonderful eyes evolved in creatures with so little brain to understand what their eyes can see.

The muscles of squid and cuttlefish evolved into another way of travel -- by jet! Their tube bodies take in water and the muscles squeeze it out suddenly, shooting the creature along. They, along with their octopus cousins, also evolved a way of hiding even out in the open, by making supplies of black ink to squirt like a cloud into the sea around them. Octopuses also evolved bigger brains, and are smarter than one would guess.

In some species of early animals, mouths gave up tentacles to grow a single big sucker, as in some eels, or to build jaws and then teeth, which became very popular. Different species experimented with inner bones and outer shells to hold their bodies together and protect them.

So, one evolutionary invention led to another, sometimes improving an old pattern a little at a time, other times by actively reorganizing available genes quite quickly to produce a new pattern. Every time a creature's DNA replicated itself in the process of forming egg or sperm cells, and every time these came together with gametes of the opposite sex, if not at other times as well, genetic information could be shuffled. Other sources of genetic change now seems to be through the activity of DNA itself, in direct response to situations, and through gene-trading bacteria moving in and out of the multicelled creatures' cells. The big mystery is just how all these processes are coordinated within and among species. Our best hope of solving it may lay in the physics of cosmic consciousness, continual creation and non-locality, as they increasingly understand fundamental levels of non-physical communications.

Looking into the past, using fossils, microscopes and other technologies, shows us that most genes existing now were developed in very ancient times, just as we already saw that bacteria had developed almost all the molecules and proteins that now exist. The new DNA development since early multicelled creatures seems to lie in the regulator genes, which organize simple genes into more complicated genetic patterns. This makes it possible to keep evolving endlessly new patterns out of the same basic genes

Some of the most fascinating of today's biological puzzles are arising in genetic engineering -- a field in which we take advantage of the microbial ability to transfer genes and get them to do it for us, though the results are not as predictable as desired. We implant genes and sometimes the microbes themselves into species we wish to alter -- to make them `better' in texture, flavor, nutrition or to resist herbicides we want to spray on their fields to kill weeds, and so on. For example, microbes emitting particular toxins are implanted into corn seed; when the corn grows up every cell contains these microbes and emits the toxins that kill insects. The puzzles arise when the implanted species remove the genes we implant, or transfer them to weeds, making them equally resistant to our poisons. We would do well to study nature's practiced ways before we leap into our own attempts to improve on them.

Much about the organization and reorganization of DNA may be better understood when we understand more about the brain. The DNA pool of bacteria, the cellular nucleus, and the brain are all natural systems for receiving, storing, and processing information required by organisms. The efficiency of the Gaian way of life in using the same schemes over and over in ever more complex arrangements suggests that these three systems are likely to have a good deal in common. We have learned that the brain is more coordinator than dictator of the body's physiology and behavior -- a kind of central clearinghouse and resource center for the body as a whole. Perhaps the organized DNA of cell nuclei is similar, not dictating what the cell does, so much as being used as a resource center by the cell as a whole.

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A step at a time, over many millions of years -- though some steps as we know were faster than others -- the seas filled with an incredible variety of living things co-evolving as ecosystems. Or, we might say, from our Gaian viewpoint, the seas with their ever renewed supplies of salts and minerals washed from land rock turned themselves into a living soup of plankton and larger creatures.

Many species continued the `plant way of life,' though they were not yet true plants, evolving seaweed colonies from simple algae. Some had parts that looked like roots, stems, and leaves, though true roots, stems, and leaves evolved only much later on land. These chloroplast-containing creatures took over bacterial ways of fixing nitrogen, took other building materials from the sea and from the sea bottom, which was rich with decaying bodies, and continued making food using solar energy. Their usable nitrogen and the carbon was taken from carbon dioxide and built into their bodies, then passed on to animals who ate the algae to build their bodies.

Some of the carbon was recycled, but much of it was buried in sea floor sediments of dead protists, algae, and animals. Over billions of years of evolution, this process plus a similar carbon burial on land after plants evolved there used up most of the early atmospheric carbon dioxide. It and other early atmosphere gases were gradually replaced by a balance of mixed gases that were almost entirely the products of living creatures and were just right for their continued survival and evolution -- gases constantly burning each other up, constantly being recycled and replenished by living creatures.

Bacteria and protists continued to live among the larger creatures in far vaster numbers, working at the rebuilding and balancing of the atmosphere and the chemistry of the seas, as well as providing the larger creatures with food. Recall that in each ecosystem, the member species co-evolve as they affect each other's lifestyles and forms. Over time ecosystems mature from a few species that may compete in a juvenile way for food and space to a mature ecosystem in which many species balance their lives cooperatively.

Plants did not become as complex as animals because nothing pushed them -- life was too easy. They had no need to go after their food, to see it, to grab it, to digest whole other creatures. Animals, who did have to do these things, tried out many ways of building themselves. Some evolved hard coverings like those of clams, snails, barnacles, spiny starfish, and sea urchins Some, like crabs and lobsters, successfully tried out legs in pairs. Others, like worms, squid, and octopus, stayed soft. Still other free-swimming forms became sharks and the bony ancestors of modern fish. But no matter how different their shapes, they all evolved muscles to move with, blood to circulate supplies, eyes to see with, and nervous systems with brains to coordinate their ever more complicated bodies.

Together, this great variety of living things created different ecosystems for themselves and for one another on the sea's floor, on its surface, and in the shallows near shore. The first such systems with large creatures appeared so suddenly we refer to them as the Cambrian Explosion. This is what we identify as the start of the Paleozoic Era -- meaning `ancient animal period' -- around half a billion years ago. Our best fossil find of this explosion of creativity is the Burgess Shale in western Canada, with a wide variety of creatures from very large soft-bodied quilted creatures to smaller armored creatures such as Opabinia, with a long, flexible but fanged vacuum cleaner hose of a mouth. Some look like moonwalkers or weird lifeforms we imagine on other planets. All together they look completely unlike any ecosystem of today, and indeed they went extinct long ago.

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The stardust that formed our rocky Earth had come a long way in rearranging itself. But while countless small bits of the planet's crust were turning into living creatures, the crust as a whole had broken into pieces that slid about on the softer molten insides, like the armor plates of an armadillo. Ever new eruptions of lava pushed the plates apart by adding cooling rock to their edges, while their opposite sides slid under the edges of other plates to make room.

We introduced them in Chapter 2 as tectonic plates, their name coming from the Greek word for `builder.' And, indeed they built the shape of the world we know. The thickest parts of tectonic plates are the land masses we call continents that stick up out of the seas. Over the past three billion years these thicker continents have repeatedly moved together and apart, with half their land mass submerged when they are most spread out. During the spread out phases, such as the one we are in now, Gaia's temperature drops an average of ten degrees centigrade, causing waves of recurring ice ages in cycles of about a hundred thousand years.

At the time the dinosaurs evolved, hundreds of millions of years after the Burgess Shale creatures, all the thick parts had moved together into one huge supercontinent called Pangaea, which means `all Gaia' -- a name chosen well before Lovelock's Gaia hypothesis. Ever since then, this land mass has been breaking up to form continents separated by oceans and seas. The Atlantic Ocean is still getting wider year by year as South America and Africa are pushed ever farther apart.

Before they became the Pangaea supercontinent, the continents had been separate, but they had then dominated what we know as the southern half of the Earth. As Pangaea formed and split up again, the continents moved northward and apart from one another. If you could see their movement over billions of years as a film, you would see them riding the slowly swirling soft insides of the Earth.

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Let's go back to pre-Pangaean times now, to the next big step in the evolving dance of life -- the great land adventure, when some creatures took to dry land and continued to evolve there.

Of the organisms that were larger than microbes, algae and funguses got to dry land first, paving the way for animals by multiplying into rich food supplies, especially by evolving into plants -- just as bacteria had paved the way for plants by breaking up rock and reproducing themselves, thus starting a supply of soil.

Perhaps the migration of creatures onto land began when the algae were left high and dry for hours every day by Moon-pulled tides. To survive, they adjusted their bodies, learning to live both in and out of water. Algae and funguses first appeared on shores, then their spores were blown further inland by wind. Wherever bacteria had made enough soil and there was enough moisture from dew or rain, such spores developed.

Fungi are a whole kingdom in themselves, including molds, yeasts and mushrooms. They dissolve rock for food by excreting acids, and digest organic food before consuming it by excreting enzymes onto it.

The first plants, evolving yet another new kingdom, were mosses growing close to the ground along with cooperating teams of algae and funguses called lichens, which look like very close-cropped plants and come in a variety of colors. It took a long while for plants to develop strong roots and taller, stiffer bodies that could evolve into ferns and trees. The major new structures plants had to develop to support their bodies in air and carry water from roots to all parts were vascular systems -- stiff tubes, or veins, running the length of plants. The whole plant kingdom is divided into vascular and non-vascular plants.

Animals followed more slowly onto land. Arthropods, the first to come ashore, are jointed -- foot creatures with their hard skeletons outside -- from the Greek, arthro meaning `joint' and `pod' meaning `foot.' Arthropods evolved in the sea -- the Burgess Shale's Opabimia was an example -- but they also learned to breathe air in coming to live on land, where some of them evolved into lightweight insects, while their relatives in the buoyant sea evolved larger bodies, such as those of crabs and lobsters. Horseshoe crabs, like sharks, are like those bicycles in a jet age -- Cambrian creatures still going strong today!

It was just as fungi, plants and insects were getting their real grip on land that the first great extinction occurred -- around 440 million years ago -- when one of Gaia's great waves of ice ages formed great land glaciers and chilled the seas. More than half of all her life forms died out -- the least affected being the adaptable bacteria and protists -- and it took her 25 million years to recover her biodiversity.

After the extinction, a new type of animal emerged from the sea. These animals, like the early shore plants, evolved ways of living part-time in the sea and part-time out of the sea. We call them amphibians -- amphi meaning `double' and bios meaning `way of life' -- creatures who live double lives, on the land and in the sea. While arthropods have their bony skeletons outside their bodies, amphibians were fishlike creatures that crawled on fins and developed lungs to breathe air. Eventually they transformed their fins into short legs, and later we will see that some species evolved into reptiles. Most of the ancient species of amphibians died out as other animals evolved. Among those still living today are frogs and salamanders.

Only a hundred million years after the first mass extinction there was a second, again related to cooling climate change, again doing in half the species of Earth. The third mass extinction happened only 37 million years later, so it took a hundred million years altogether for full recovery. During that recovery plants had their time in the Sun, as we say -- great carboniferous forests with giant tree ferns, ginkos and cycads growing up and thriving for 70 millions of years, generation by generation, removing carbon from the atmosphere and burying it with their bodies as they were pressed underground to become coal and oil. It was during this era that Pangaea the supercontinent was assembling herself from older pieces named Laurasia (which would later again break off to form Asia, Europe and North America) and Gondwana (which later broke off to form South America, Africa, Australia and Antarctica).

Insects thrived in the great forests; amphibians moved inland, inventing self-contained eggs and splitting into two lineages: the synapsids -- meaning `with arch' (in their bony skulls) -- that evolved into large four-footed tetrapods that evolved in turn into mammals and humans, and the second lineage: the reptiles that evolved into turtles, snakes, lizards, and archosauromorphs -- meaning `ruling lizard forms.' (Note: archeo means ancient, archo means ruling.) Guess which became our favorite dinosaurs and pterydactyls.

In that great age when the ruling reptiles stalked the Earth as the largest of its creatures for 160 million years -- two to three times as long as mammals have been around, some forty times as long as humans have existed. The fossil record shows many shapes and sizes of reptiles and lets us know what important roles they played in evolution. But a quarter billion years ago, just as the first lizard began gliding through the air near the end of the Paleozoic era and before our favorite huge beasts appeared, 95 percent of all existing species disappeared in the fourth and greatest extinction. About the best thing we can say about it is that its recovery period -- the Mezozoic, or `mid-animal-era' -- brought the world an explosion of color in flowers along with triceratops, brontosaurus and early birds.

Flowers, those marvelous sex organs with their wonderful blaze of color, brought a special kind of beauty, but that beauty was practical as well. With flowers, plants achieved their full two-parent sexuality, but with both sexes housed in the same individual. Sitting still in one spot, they needed a way to spread their genes around to other potential mates they could not reach themselves. Flowers gave plants a way of attracting birds and insects to cooperate with them in getting the male pollen of one plant to the eggs of another.

It is interesting to note that 60 percent of all known species are insects, while less than one percent include all birds and mammals! One third of the insect species -- one fifth of all species -- are beetles. It would be easy to argue that beetles, with their four-winged armored bodies are the most successful of Gaian creatures.

Birds, we can see clearly, descended from the still half-reptile archaeopteryx -- `ancient wings' -- and its cousin the pterodactyl -- `feather fingers' (both the words `wing' and `feather' come from the Greek root ptery). Their fossils, as we said earlier, show us leg bones evolving into wing bones, jawbones into beaks, scales into feathers. These early birds were far larger than today's, with wing spans up to twelve meters. People build flying models of them to see how such great beasts could stay in the air.

The great beasts of the Dinosaur Age grew up to twenty-seven meters long and some species towered very tall on their hind legs. Scientists still argue about just what dinosaurs were, and at present it looks as though they were rather odd creatures -- neither reptile, nor mammal, nor bird, but with elements of all three. During their reign, the land world buzzed with flying and crawling insects and grew ever greener with plants and their colorful flowers. In the sea world, lovely protists were filling the oceans to recycle minerals, while great marine lizards called mosasaurs and icthyosaurs -- `fish lizards' -- swam over bottom-dwelling ammonites and clams and other creatures.

Late in the age of dinosaurs, therapsids were evolving into true mammals with a kind of croco-dog-bear look, just as archaeopteryx and pterodactyl were transforming their lineages into birds. Warm-blooded mammals, who keep their own body temperature constantly warm, as dinosaurs seem to have pioneered, and keep their babies inside their bodies, rather than in eggs, until they are ready to be born, were the last kinds of animals to evolve. Though mammals and birds were until not long ago thought to be the only warm-blooded creatures, we now know that some fish, as well as some dinosaurs, also evolved this feature. Red-blooded tuna, for example, keep much warmer than the surrounding sea, with systems that are extremely efficient in preventing heat loss.

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The really big boost to mammalian evolution was given by the same catastrophic event that spelled utter disaster for dinosaurs. About 65 million years, the Mezozoic era ended abruptly as a huge meteor plunged into what we now call the Caribbean, first incinerating life, then freezing it in cold temperatures as a black cloud of debris spread around the Earth, causing the fifth great extinction -- the last until we humans initiated the present sixth one!

The great dinosaurs disappear, as do archeopteryx and pterodactyl, from the fossil record after this great catastrophe. The weather, the climate, the whole environment on which they depended was gone and the huge specialized creatures who had ruled Gaia for so long could not change fast enough to survive such sudden change. But just as new types of bacteria took over when many of Gaia's early bacteria had died of oxygen poisoning, new kinds of animals evolved now from the small ones left after this great extinction. Gaia has shown again and again the ability to recover from disasters, always continuing the dance of life in creative new ways.

So life continued in the new age, the Cenozoic, with particular species of plants and animals evolving particular bodies and ways of life to balance and harmonize with one another as parts of the great Gaian system in which they evolved -- a system that went on working as a single being to regulate the Earth's temperature, chemistry, and weather.

Living things may even help tectonic plates to move by weighing them down as their bodies turn back to rock, or at least by providing chalky layers that help some of the weighted plates slide under the edges of others. Pangaea was breaking up, splitting Africa from South America and separating Greenland out between America and Europe, the Atlantic Ocean flowing between all these pieces. India, at that time, had moved about halfway from Antarctica, where it began, toward Asia, where it was to get stuck in place, pushing up the Himalayas as it crunched into the greater landmass.

Somewhere around 50 million years ago, just before India struck Asia, it pushed the seafloor up, forming a warm shallow sea called Tethys that teemed with plankton life and lured some early wolf-like creatures back to the aquatic life. This is the apparent origin of the sea mammals we call cetaceans, which include whales and dolphins. First the wolf-like creature reverted to a sort of hairy crocodile amphibian stage, then they took seriously to the seas, giving up fur and feet for smooth skins and flippers. Pinnipeds -- `fin-feet' -- also became aquatic mammals, such as sea lions and walruses.

The Earth was beginning to look as it does today, though the continents were still closer together than they are now. As land bridges between them disappeared under water, plant and animal species were stranded on separate continents to continue separate paths of evolution. This is why many species alive today, like the kangaroos and koalas of Australia, are found only on a particular continent. Some species of different continents, such as the alligators of North America, the caimans of South America, and the crocodiles of Africa, are still recognizable descendants of the same Pangaean ancestors despite differences due to their later evolution.

Remaining reptiles in the Cenozoic were, as they still are, cold-blooded animals, their body temperature rising and falling with the temperature of their environment. Like the birds descended from them, we saw that reptiles lay eggs. But unlike warm-blooded birds, they rarely take care of their young. Their brains are so simple that most reptiles can't even recognize their own babies when they hatch. In fact, they have been known to eat their own babies -- not because they are vicious or cruel, but because they cannot seem to tell the babies from other edible things. This challenge to reptile babies made them evolve into creatures that run very fast very early. A baby reptile, in fact, is almost as good as a grown-up at doing most everything reptiles do.

Reptile behavior emerges directly from reptile genes, bodies, and physiology, without benefit of very much thought or choice. They do pretty much the same things in the same old ways, not having enough brain to think about or change them. They hunt food, show off to win their mates, huff and puff at strangers who come into their home territory, and fight if the stranger is not frightened away. That's about all. They don't even sleep, but just settle down quietly when night cools them off.

Early mammals were quite different, with their lively warm-blooded bodies, the female ones keeping their offspring inside until time for birth and feeding them on mothers' milk from the mammary organs which gave them their name. Many early mammals were active by night, having evolved a pattern of waiting till dinosaur types went to sleep before going about their business. These included small tree-dwelling primates with stereoscopic depth vision adapted to seeing in the dark and nimble fingers to pluck their food from branches. They carried their young on their backs as they swung nimbly through the trees.

True mammals branched into two types. One branch, the marsupials, which includes kangaroos and opossums, gives birth to very undeveloped babies that stay in pouches on the outside of the mother's body after they are born, until they are ready to live on their own. The other branch grows its babies to a later stage deep inside the body until they are born.

Some of today's small mammals show links back to the early mammals that evolved from reptiles. The platypus, for instance, is a strange, furry, warm-blooded aquatic animal that lays eggs and has a duck-like beak and webbed feet, as though it couldn't decide whether to evolve into a bird or a mammal. A few mammals later devolved their legs back to flippers and fins when they returned to the sea to become seals, sea lions, manatees, whales, and dolphins.

Possums are one of the most primitive, or antique, species of mammal living today. They seem to have changed little since they evolved among the dinosaurs, so they are important in the study of evolution. Among other things, they may have been the first animals to sleep and to dream.

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