by Ian Mccallum
Under the massive weight of oxygen-free water, the second stage of the cycle began. In a process of geological transformation, layer upon layer of the exfoliated and eroded igneous tissue compressed to become the oldest known sedimentary rocks on Earth. The crystals in these strata, under intense heat and pressure, were transformed in the third stage into the tough, elegantly grained metamorphic form that we find in the present-day mountain ranges such as the Alps and the Himalayas.
As a metaphor for the shaping of human life and character, it would appear that our personal fine- and coarse-grained life experiences, our patterns of weathering, trauma, and transformations are not unlike those patterns in the cycle of stones. Meanwhile, it is curious to think, as British geologist and archaeologist Jacquetta Hawkes puts it, that
granite and basalt, with water, nitrogen and carbon dioxide in combination with the early atmosphere of Earth, have made all the material paraphernalia with which man now surrounds himself, the sky-scraper, the wine glass, the vacuum cleaner, jewels, the mirror into which I look. And the woman who looks? Where did it come from, this being behind the eyes, this thing that asks? How has this been gleaned from a landscape of harsh rock and empty seas?
GEOLOGICAL TIMESCALE
It would seem that we cannot escape our molecular and geological foundations. They are in our blood.
ORGANIC LIFE
With the unraveling of DNA sequences in living forms, most biologists now acknowledge three domains of life. These are the Bacteria—the conventional microbes of the world; the Archaea, ancient single-cell organisms that inhabit environments of extreme temperature and acidity (thermacidophiles), salty environments (halobacteria), and anoxic bogs (methanogenic bacteria). The third domain comprises the Eukarya—organisms that are made up of cells with organelles and a separate, membrane-bound nucleus. The Eukarya comprise the fungi, the plants, and all animals, including us.
The Archaea were the first organic inhabitants of the Earth.Without them, there would be no trees, flowers, or fish…and we wouldn’t be here either. But when and how did they come about? As for the when, we believe it to be about thirteen or fourteen cosmic years ago (3 billion years). The how is speculative but highly likely. With 60 percent of the granites already established, the electrochemical mixture of land, water, and lightning combined to produce molecular compounds of nitrogen, carbon, and other elements that had not existed on Earth before. There was no turning back. A process had been initiated in which the electrically charged molecules combined to form water-borne organisms capable of living in an oxygen-free world. The next step in the process was crucial: the development of a membrane—the first organic boundary, the first fence, the first hint of specialization.
However, if there was ever a defining moment in the evolution of life as we know it, it occurred about ten cosmic years (about 2 billion years) ago. It marks the earliest evidence of one of the great strategies of species survival: symbiosis—so named by German botanist Anton de Bary in 1873 to describe the living together of different organisms for mutual benefit. With it came the emergence of the first differentiated cells. These were the first cells to have organelles and a nucleus with its own membrane. The reason for the nuclear membrane will become clear. But what triggered this first symbiotic relationship? It was the changing conditions of the surroundings.
In an environment that was becoming increasingly oxygenated, new aerobic (oxygen-coping) bacteria began to emerge, putting them at a clear advantage over the anaerobes. With competition for nutrients becoming increasingly serious, including a phase when, in all likelihood, the two strains of bacteria were feeding off each other, the first great alliance took place. Instead of being devoured by the predatory anaerobes, the more recent, threadlike aerobic organisms became part of the intracellular structure of their evolutionary older anaerobic cousins. They literally came on board, where they function to this day in all living cells, as the indispensable organelles responsible for the conversion of oxygen into energy. Essential for cellular metabolism and homeostasis, these little subcompartments of our cells are known as mitochondria, from the Greek mitos, meaning “thread,” and chondrion, meaning “granule.” Because of the energy they generate, they are also called the powerhouses of the cells. Without them we would not be able to move, think, or dream. Without them, the animal and insect kingdoms as we know them today would not exist.
The symbiotic relationship, however, was a conditional one. The host cells, compelled to protect their own DNA, ensured their long-term survival by developing a membrane around their nuclei. The mitochondria, for the same reason, developed a double membrane. This genetic independence of the cell nuclei and mitochondria brings a fascinating twist to the symbiotic tale. It is well known that the genetic information in the nucleus of mammalian cells comes from both parents. What we didn’t know until very recently is that the genetic information in the mitochondria is passed on, generation after generation, by the female of the species only. In other words, the mitochondria, the powerhouses of our cells, come from our biological mothers. Why there is no contribution from the biological father is unknown, but it would seem that the genetic information, if any, which the sperm may carry regarding the mitochondria is either absent or, if not, lost or destroyed at the moment of conception. Be that as it may, the maternal link to our mitochondria has opened up a fascinating avenue into our understanding of human ancestry. With the discovery of this lineage, we are able to show that modern humans, Homo sapiens sapiens, as little as 200,000 years ago shared not only a common bloodline, but as recently as 60,000 years ago, a lineage through six or seven possible biological mothers. As humans, it would seem that we are more closely related to each other than we sometimes like to think. As for our link with animals, the evidence suggests that the mammalian bloodline goes back 100 million years. It would appear that the poetry of the brotherhood and sisterhood of all living things has become science.
A similar symbiotic process occurred in plant cells as well, but where the new bacterial tenants (cyanobacteria) are what are known as chloroplasts—the “green stuff” of plants. Instead of using oxygen, they combine carbon dioxide with water and light to produce oxygen. As with mitochondria, chloroplasts too, have their own DNA.
It should therefore not be surprising to learn that other biological partnerships followed. One of the most important of these partnerships is described by the science writers John Briggs and F. David Peat in their book Turbulent Mirror as “the taking into the cell in another intrusionturned- marriage the highly mobile, corkscrew-shaped bacteria”—the spirochetes. Once again, in return for nourishment and protection, the spirochetes, or “wrigglers,” as neuroscientist and author Lynn Margulis calls them, made their sluggish hosts an offer they couldn’t refuse. They brought with them their stout cilia, or hairlike propelling strands, to act as miniature outboard motors for their new hosts. Could this have been a hint of the future legs and wings to come? Perhaps so, but not all wrigglers became propelling mechanisms. Some of them developed into microtubules within the host cell, eventually joining and elongating to become what is believed to be primitive axons and dendrites—the “business ends” of neurons, as Margulis describes them. As she suggests, it is not improbable that the growing network of connecting tubules developed into neurological tissue and later, much later, the first brains.
Moving on to four cosmic years ago (900 million years), we would have found ourselves in the company of the planet’s first multicellular plants. Known as stromatolites from the Greek stroma, meaning “matrix” or “tissue,” they established themselves in networks of algae or algal beds. One galactic turn later we would have seen the first jelly-fish, coelenterata, and only two cosmic years ago, the trilobites—the world’s first insects. Marine and land invertebrates were developing their first shells, or exoskeletons, and then came the glaciation of an African landmass very different to its modern shape. With the receding of the ice roughly one and a half cosmic years ago, the sea became home to
horn corals and boneless fish—the predecessors of modern sharks.
With a steady increase in temperatures, the Earth produced its first tree ferns, sharks, and early amphibians. The stage was set for what seemed to be an inevitable explosion of life, but it was not to be. Instead, as a result of large-scale volcanic activity and global warming, carbon dioxide levels rose to toxic proportions, wiping out 95 percent of the Earth’s species! This catastrophic occurrence, a fraction more than one cosmic year ago and now referred to as the Permian Extinction, heralded a new geological period on our planet—the Triassic. The survivors regrouped themselves. New forms began to take shape, among them the ancestors of modern turtles, sharks, and the much-maligned crocodile, surely the greatest survivor of all modern animals. Gymnosperms (our nonflowering trees and plants) began to carpet many parts of the world, contributing not only to an increase in the Earth’s atmospheric oxygen, but to a change in the weather too. Increasing forestation meant increasing rainfall. The rivers began to flow freely, providing a niche for countless riverine plants, fish, and insects. Nine “months” (180 million years) ago, in a new period known as the Jurassic, the dinosaurs (from the Greek words deinos, meaning “terrible,” and sauros, meaning “lizard”), became the food-chain champions of the world.
A “month” later, accompanied by a splash of colors, plants with sexual organs made their first appearance. The flowers of the fields opened their petals and sepals to expose stamens and pistils—the respective male (pollen producing) and female (seed producing) components of flowers. Drawn to the plethora of colors and perfumes came an equal plethora of unwitting pollinators in the forms of wasps, flies, butterflies, and bees.
Spiders and crustaceans introduced themselves to the Earth’s ecosystems at about the same time as the flowering plants, while behind the scenes, a group of dinosaurs (they weren’t all as big as Tyrannosaurus rex) evolved a new way of escaping their larger, hungry relatives: their scales softened into feathers. Examine a reptilian scale through a powerful microscope and you will discover that its molecular architecture is practically identical to that of a feather.And so it was, only seven “months” (about 130 million years) ago that Archaeopteryx, the first known feathered creature (with teeth!)—a true ancestor of the birds—took to the sky. Escaping predators was a huge benefit to the winged creatures, but there were other advantages as well: flight provided new and wonderful opportunities for insulation, feeding, nesting, and travel.
At the same time the birds (now warm-blooded) began taking flight, the Earth’s surface began to split up again. It was the start of a significant land migration, otherwise known as continental drift. This major breakup and spread of the southerly landmass took about four cosmic months (70 million years) to give us the recognizable continents of South America, Africa, Antarctica, and Australia as well as the subcontinent of India. The Earth’s anatomy, like a huge geological embryo, had, in a sense, differentiated itself.
Need we be reminded that the same pattern of anatomical differentiation occurs in every living embryo, from stem cells to livers, kidneys, hearts, spleens, and brains? Is global anatomy a metaphor worth taking seriously? Can we learn from our own bodies? To me, the human anatomy is one of the finest examples I know of biological differentiation and diversity. It is a living definition of ecology, an embodiment of the interactions and interdependence between molecules, cells, tissues, organs, and systems, sensitive to both inner and outer environments. Sociologically it would appear to be the same—we are a body of humans, drifting and differentiated at the same time, interacting and relating to each other and we do it because we have to. As we shall see, it is part of our survival as biopsycho-social beings.
A little over three cosmic months ago (65 million years), not too long before the establishment of the continents as we know them today, the dinosaurs’ reign ended. It is chillingly speculated that the cause of this abrupt end to the dinosaurs’ 120 million-year existence was a massive asteroid impact on the Yucatan peninsula of present-day northern Mexico. It is thought that the event caused so much dust to be thrown into the atmosphere that the sun all but disappeared from the sky. The resulting drop in temperature was so severe that the sun-dependent creatures stood no chance of survival.
How do we know that this theory is the correct one? Well, we don’t know for sure, but it seems to be the most likely one. What we do know is that there was indeed an asteroid impact as described. The element iridium is the signature of asteroid impacts and there is plenty of it in a huge but well-defined area on the Yucatan peninsula. It is dated to 65 million years ago. We also know that the dinosaurs made their surprisingly rapid exit at about that time. As plausible as they might seem, two contending theories—a decimating epidemic or an intolerable atmospheric/ climatic change of another kind—have not been substantiated. Of the three possibilities for extinction, which one could the human animal be facing?
And so, in what could be described as a huge coincidence, the demise of the dinosaurs gave the burrowing, warm-blooded placentals, class Mammalia, the opportunity to establish themselves. While this is our class, there were no mammalian forms at that time even vaguely ready to put up their hands or wiggle their thumbs. The geological period known as the Cretaceous, from the Latin word for “chalk,” had ended and a warm-blooded class of creatures tentatively tiptoed into the Tertiary. The burrowing lemurs, shrews, rats, and mice showed their daytime faces. Ancestral ungulates and other ancient carnivores announced themselves, along with a fresh spurt of newly evolving birds, insects, frogs, worms, mosses, and flowering plants.
AFRICAN ORIGINS
About two cosmic months ago, the Great Rift Valley began to open up and, peering into it and out of it, were the tiny evolutionary cousins of the elephant, the family Procaviidae—the hyraxes of bush, trees, and rocks. The aardvark and the early rhino made their acquaintance with Africa about one “month” ago. Then, with the worldwide expansion of grasslands only twelve cosmic days later, the hollow-horned antelopes showed up alongside their slightly older ruminant companions, the giraffes, with their horns of solid bone. Bulk-feeders such as the buffalo, Syncerus caffer, began herding themselves out of Europe and into the African grasslands while the zebra (family Equidae), whose ancestors hail from South America, declared their savannah stripes. As if to balance the wilderness equation, the modern carnivores, such as the lion and the hyena, left their European origins to become part of the African food chain. This all took place about six “days” (3 to 4 million years) ago.
Twenty-four cosmic hours later, not far from the foothills of the newly formed volcanic slopes of Kilimanjaro, an astonishingly odd-looking primate stood up. It was an apelike being of the genus Australopithecus (from the Latin australis, meaning “southern,” and the Greek pithekos, meaning “ape”). Genetically different to the hominids that are linked to modern orangutans, these bipedal creatures of the subfamily Homininae, now extinct, are our earliest hominid ancestors.
There appears to be little doubt about who our early ancestors are, but what is unclear is our ancestry—the line of descent. From Australopithecus to modern man, what we do know, however, is that the progressive increase in brain size of our intermediate ancestors and, with it, a consciousness that would eventually define the human animal, has the quality of a quantum leap. The diminishing gaps in time between the increments has forced us to revise our notions of evolution as something slow and purposive. Let’s have a look at these leaps.
With a brain size of 750 cc, Homo habilis, our original hominid grandparents, appeared on Earth about four cosmic days ago (2.5 million years). It would appear that they lived in an overlap phase with their smaller-brained but similar-looking cousins, Australopithecus africanus and A. bosei. One animal among many others alongside our Australopithecan cousins must have been watching the early development of the hominid family. It was the African elephant, Loxodonta africana, who emerged from its own ancestral line at more or less the same time as H. habilis, the world’s first
toolmakers. Habilis, from the Latin habilis, meaning “dexterous,” is linked with the first discovery of concentrations of animal remains, as well as stone collections, many of which had been brought from long distances. These pebble tools, choppers, and waterworn cobbles crudely flaked on one side to form a jagged cutting edge, were mankind’s first embellished stone tools.
Habilis, along with having a wider range of equipment, also had a different arrangement of teeth to those of their Australopithecan relatives. They were, indeed, a different species. The back teeth of these toolmaking hominids were narrower, suggesting the development of an important change in their diets—they were eating more animal food than their mostly vegetarian ancestors. As for the size of the habilis brain, not only was it larger than that of Australopithecus, but, for the first time, the bulge of Broca’s area, the convolution of the brain corresponding to the center for executive speech, became evident on a primate skull.
In their book The Wisdom of Bones, Alan Walker and Pat Shipman remind us that the anatomical capacity for speech is also a reflection of other particular mental abilities, including the ability to categorize and analyze the world in a complex fashion. It includes the capacity to name and to talk about things, as well as to describe actions without performing them. The Earth had a new tongue. Our early hominid grandparents were not only the carriers of stones and bones, they were also the carriers and shapers of words.
About one and a half cosmic days ago (a million years), Africa was witness to another sudden leap in the size of the hominid skull. Homo erectus emerged with a 1,200–1,300 cc brain. Also known as Homo ergaster, or “The Work Man,” these ancestors brought with them an up-to-date tool kit containing a variety of large, symmetrically flaked stone bifaces, or hand axes, for chopping, cutting, piercing, and pounding. They, too, were anatomically different to their immediate ancestors. Compared with habilis, the faces of erectus had become smaller as well as more expressive, while their evenly spaced and smaller back teeth confirmed the early shift from a primarily vegetable diet to one that included significantly more animal protein. This increase in brain size was believed to be a reflection of the cognitive requirements for cooperative hunting and living as well as for the evolutionarily significant gift of storytelling and symbol formation. It was also associated with the capacity to harness that great element of the gods—fire.