During his acclaimed television series, The Ascent of Man, Jacob Bronowski took a moment to look directly into the camera and ask viewers what the probability might be of chemical elements coming together randomly to form a single human being? His point was clear: such a probability is zero! The likelihood of random chemistry coming together to form a weed or even a bacterium is similarly impossible. Bronowski's point was simple: complex life forms are the result of developmental programs that came into being and were slowly elaborated over more than three billion years. Innovations were initiated during particular times and became the template for further modification over time.

For evolutionary biologists, the concept of innovation has been contentious over many generations. Does innovation arise from the gradual accumulation of small steps? Or does it depend on the “emergence” of new traits, suddenly becoming the “platform” for new trajectories? Obviously, small changes in base-pair sequence are likely to yield small changes, but the accidental duplication of an entire gene may open more significant possibilities. Surely, both have contributed to evolutionary innovations; they have an historical past, arose within a period of time, and may have determined the future in extraordinary ways. Modern human societies have, in fact, become one of the most extraordinary innovations in the history of life. We ourselves, and all other living things, are the product of a very long history. The record in the rocks, our own development from a single cell, and the genes within our bodies, all bear testimony to a very long epic.1 Let's review this grand trajectory of life's elaboration—and human achievement—by dividing it into ten major stages.

1: LIFE'S ORIGIN

Surely, the first major step in our story was the origin of simple life itself. Having left no trace, the earliest attempts at biochemical organization and biophysical energetics were likely devoured by their successors. Protein synthesis within a protective vesicle allowed for metabolism. RNA conveyed instructions within the cell, while DNA carried information across generations. Today, bacterial-grade cells are the simplest forms of life. Able to gather and utilize energy, to grow and replicate, bacteria can transfer the information for all their life activities from generation to generation. These are the hallmarks of life.

Today, life arises only from living cells already formed. All your membranes, mitochondria, and cytoplasmic architecture were derived from your mother's egg cell. (Dad's sperm cell added a set of chromosomes to begin your existence, but little more). You began as a single cell, as does all other life! Only two aspects of living cells are never formed de novo: cell membranes and the DNA helix—all the other stuff can be built anew. How then did life begin?

A very unusual aspect of the living world is that, while DNA is life's fundamental information carrier, Bacteria build their DNA in a fundamentally different way than do Archaea and Eukaryota. Add this to Eukaryota having Bacteria-like operational genes and Archaea-like informational genes, and you understand that some biologists believe that there may never have been a “first living cell.” Instead, early life may have arisen from an organic ecosystem: “a community of quasi-cellular entities that exchanged genes and evolved collectively and from which the three domains of life crystallized.”2 In fact, early viruses may have shuttled genes around between these early life forms in the vicinity of deep sea alkaline vents, in temperatures well below the boiling point of water.

Some scholars have claimed that organic chemistry can exhibit inherent self-organizing properties. These properties, they argue, gave rise to replicating structures spontaneously. Indeed, proteins fold themselves into complex shapes automatically, based on how specific amino acids are arranged along their length. All that was required was a stable aquatic environment, organic molecules cooperating together within enclosing vesicles, various energy sources to power replication, followed by millions of years for trial and error. Indeed, given the proper conditions and sufficient time, life's origin on planet Earth may have been inevitable.3

2: CAPTURING THE SUN'S ENERGY

With cellular organization and reproduction in place, bacteria could use a variety of chemical reactions to keep themselves going. But metabolic reactions were restricted to special environments with energy-yielding substrates. The second major advance in our grand epic was capturing the energy of sunlight to build complex organic molecules. Purple photosynthesizing bacteria were probably the first to achieve this breakthrough. Using the energy of sunshine, they acquired hydrogen from a variety of sulfur compounds. Unfortunately, hydrogen-yielding sulfur compounds can be hard to find. Oxygenic-photosynthesis overcame this limitation by acquiring hydrogen directly from the water molecule. Here was a way of obtaining energy-packed hydrogen atoms just about anywhere on the sunlit Earth! By uniting hydrogen-—torn loose from water—with carbon dioxide, oxygenic photosynthesis by Cyanobacteria transformed the energy of sunlight into energy-rich carbohydrates, while releasing free oxygen to the atmosphere. Chlorophyll and its associated pigments are the central players in this dance of sunlight, physics, and chemistry.

Once life on Earth had learned how to rip apart the water molecule and build energy-rich foods, organic evolution began its grand progression. Ignoring the second law of thermodynamics—where everything runs down—oxygenic photosynthesis provided the energy needed to run the complex dynamics of metabolism and other life activities.⁴ Over time, this same energy allowed things to get more complicated. That was the good news; the bad news was that Cyanobacteria were polluting the atmosphere with a very nasty poison—free oxygen. Highly reactive, oxygen is a lethal threat to many forms of life. (Oxygen-averse bacteria are still with us today, active only in oxygen-poor niches.) But calamity for some was opportunity for others, as a new lineage of bacteria invented oxygen-consuming respiration. By tearing carbon dioxide out of a simple carbohydrate, and uniting the remaining hydrogen with oxygen, respiration provided more energy more efficiently.

3: A LARGER MORE COMPLEX CELL

The third major stage in the history of life was the development of the larger eukaryotic cell. Characterized by having a nucleus (within which the chromosomes are protected and replicated), these cells are a thousand times more ample in volume than the average bacterium. Central to their success was acquiring mitochondria, bacteria-size organelles in which respiration breaks down carbohydrates to provide energy for the larger cell. Oxygen-consuming respiration yields over ten times more energy than is gained from the fermentation of simple sugars. With their efficient little mitochondrial fuel-cells, eukaryotic cells were able to process more information and become more complex.5

Meiosis and the production of sex cells allowed for both the repair of genetic information and a lottery of new allelic combinations as the union of egg and sperm produced a new generation. Sex provided for a continual remixing of hereditary traits, facilitating adaptation to changing environments and evolving pathogens. Eukaryotic cells were the platform from which life's complexity advanced.

Similarly, the incorporation of yet another bacterial partner within a eukaryotic lineage marked another major advance. This new partner was a cyanobacterium, carrying with it the power of photosynthesis. These new endosymbionts became transformed into chloroplasts, allowing green algae to become photosynthesizers themselves. Red algae, brown algae, and several other lineages acquired additional photobionts as well. Algae of all kinds, together with the activities of the Cyanobacteria, expanded oxygen-producing photosynthesis around the world. Slowly, our atmosphere became breathable.

4: MULTICELLULAR LIFE

The fourth major stage in our continuing epic of progressive change was building larger, multicelled, organisms. Originating independently in three eukaryotic lineages, this new process gave us the three great kingdoms of larger living things: plants, fungi, and animals. Each of these kingdoms constructs its multicellular forms in entirely different ways. With cell walls made of thin membranes, animal embryos can undergo complex development, involving both cell migration and self-dissolution. Fungi build their larger forms, whether toadstools or lichens, with hair-thin hyphal threads, elaborately woven together. In contrast, algae and land plants have cells whose walls are built of stiff cellulose. One of the world's most complex polymers, cellulose builds brick-like cells, strong but static, which is why plants find it so difficult to move.

All multicellular life forms, regardless of the kingdom, require cell-to-cell adhesion and sophisticated intercellular communication. Systems of intercommunication are essential both for growth and structural integrity. In fact, all multicellular beings are constructed of eukaryotic cells. Apparently, the greater information-carrying-capacity of the eukaryotic cell was a necessary prerequisite for the construction of complex multicellular life. Without the mitochondria-powered eukaryotic cell—and an atmosphere rich in free oxygen—the world could not have produced larger, more complex, multicellular beings.

5: ANIMALS ARRIVE

By my count, the fifth major stage in the advance of life's complexity was the development of larger and more active animals during what has been called the Cambrian explosion. As we discussed in chapter 7, around 540 million years ago (mya), the world's oceans suddenly became home to a zoo of different animal lineages! Worm-like animals, shell-bearers, and many-legged crawlers all appear together at about the same moment in time. Many of these creatures developed eyes to see where they were going, and chewing mouthparts to devour one another. The paucity of trace fossils—such as worm trails and foot-prints—makes clear that animals were miniscule in earlier times. An atmosphere with increasing oxygen pressure was likely the key factor, allowing respiration to power both larger creatures and more active pursuit in the animal world.

Though oxygen-consuming respiration may have powered larger, more complex, animals, it didn't build them. Increasing complexity required more elaborate developmental protocols. Over time, accidental gene duplication provided the wherewithal for new developmental pathways. These more varied instructions produced an increasingly diverse fauna. Preceded in the fossil record by the enigmatic Ediacarans, who then declined, the sudden appearance of Cambrian animals marked another grand advance in the history of life.

6: PLANTS PIONEER THE LAND

The sixth major advance in the history of life, and surely one of the most important for the diversity of the living world, was the colonization of land by green plants. With embryonic tissues at their growing tips, land plants elaborate many forms, from weeds to trees, and spores to flowers. Once land plants had acquired lignin-strengthened cell walls and a more efficient plumbing system, they grew larger and more complex. With a tubular cambium, expanding in strength and fluid transport every growing season, woody trees formed tall forests. Land plants added organic matter to the soil, reduced erosion, provided moisture and shade to those within the understory, and nourished a terrestrial fauna.

Another singular botanical advance came with the development of ovules and pollen, giving rise to seeds. Carried by the wind or animal vectors, pollen grains germinate near the ovule to effect fertilization. Pollination supplanted swimming sperm, allowing seed plants to reproduce in drier habitats and create a broader variety of biomes. As plants pioneered land surfaces, a number of animal lineages began their own terrestrial diversification. Of these, one has become preeminent.

7: VERTEBRATES CONQUER THE LAND

From a human perspective, the seventh major step was the emergence of land vertebrates. Similar to land plants and insects, four-legged vertebrates arose from fresh-water environments, beginning their advance onto the land about 370 mya. Here was a lineage of animals that could grow large, defy gravity, move quickly, and build more complex brains. A terrestrial flora, supporting insects, spiders, worms, and snails, made it possible for early land vertebrates to find food. Ever since their origin, vertebrates have been the largest terrestrial animals. We humans bear uncomfortable witness to the rise of land vertebrates, choking readily because air and food passageways are not clearly separate in our throats—just as in our fish-like ancestors. Gill-depressions that come and go during early human embryonic development are further evidence that we arose from fish. Four limbs and a many-parted backbone are additional testimony to our tetrapod vertebrate heritage.

Though life rebounded after the massive Permo-Triassic extinction 250 mya, biodiversity was clobbered yet again with the end-Cretaceous extinction event 65 mya. This last extinction, with ongoing volcanic activity punctuated by an asteroidal blast, obliterated the most charismatic lineage of land animals: the dinosaurs. Dominating the world's landscapes for over 200 million years, only birds remain as living descendants of these extraordinary animals. That was the bad news; the really good news was that smaller furry creatures suddenly found themselves in a less dangerous world. After the departure of the dinosaurs, and already represented by a number of lineages, furry mammals diversified explosively. Fortunately, and in advance of the end-Cretaceous extinction, Mother Nature had fashioned yet another grand advance in life's diversity.

8: FLOWERS, FRUITS, AND GRASS

The eighth grand advance, I'm convinced, was the development of the flowering plants (Angiosperms). Ranging from little floating pond weeds to orchids and baobab trees, flowering plants come in an extraordinary variety of shapes and sizes. Whether counted by species number or standing biomass, they make up the vast majority of terrestrial vegetation, providing both architectural variety and nutritious abundance. Of their many clever adaptations, getting animals to carry pollen grains from one colorful flower to another was a significant advance. Not only did the flowering plants use animals as pollinators, offering them sugary nectar, they also supported many animals with a grand variety of yummy fruits and nutritious seeds. Having enclosed their seeds in a special encasement, flowering plants were able to fashion everything from the little grass grain to the soybean, tomato, pumpkin, and coconut. Flowering plants, together with their animal pollinators and fruit dispersers, have grandly expanded biodiversity over these last one hundred million years.

Another recent innovation has also been transformative, both in drier ecosystems and for human history itself. This was the expansion of grasslands. While grasses may have existed before dinosaurs were extinguished, they have become important only in more recent times. Antelope, deer, cattle, and horses all increased in numbers as grasslands have expanded around the world over the last thirty million years. Because their slender stems grow from a tufted and protected base, grass survives both fire and grazing. With the spread of C₄ grasses about six million years ago, fire-prone grasslands have expanded their dominion in warmer and drier environments.

9. A TWO-LEGGED PRIMATE GETS REALLY SMART

As the pageant of life continued, flowering trees inspired the evolution of monkeys and, later, fostered the evolution of swinging apes. Stereoscopic vision and social lives had given primates larger brains. With more erect bodies, flatter chests, broader shoulders, and highly versatile forelimbs, the swinging apes became brainier yet. No other group of animals can swing their arms around the way we Homonoids do. Around the same time, expanding grasslands in seasonally dry habitats promoted the proliferation of large mammalian herbivores. These four-legged nutrient-rich resources, in turn, allowed a two-legged African ape to triple its brain volume in only three million years. Recall the TV advertisement in which the old lady asks, “Where's the beef?” The answer from an ecological view is simple: “On the grasslands and savannas!” There isn't much beef-biomass in dense evergreen forests; instead, broad open grasslands support extensive populations of grazers. Though omnivorous, our ancestors knew that large grazing animals provided food of the highest quality. Moving on two legs allowed our ancestors to throw rocks, fashion spears, and become effective hunters.

Rather like small colonies of ants, human bands began behaving as “super cooperators,” competing with other human groups for access to food and water. Group bias, ethnocentrism, and the grand divide between “us-and-them” are the consequence of our evolutionary past. We are a tribal species whose primary environmental antagonists were other tribes. Surely this is the dynamic that drove brain expansion in close synchrony with the elaboration of speech. Rapid vocal communication empowered a cooperative coalition of males to protect their territory and resources. Inter-group competition not only expanded the human brain, it drove us out of the tropics into ever-more challenging environments. By carefully fashioning tools and weapons, cooking food to make it more digestible, and with language springing from our lips, humans became the most versatile animals to ever walk the Earth.

I disagree with those scholars who have imagined a sudden advance in human intelligence around 100,000 years ago. Yuval Harari crystalizes this notion as a “Cognitive Revolution.”6 Expanding three-fold in three million years, I suspect our intelligence expanded slowly over that time period, refining our speech, expanding our imagination, and giving us ever-more sophisticated social interactions. The expansion of sapiens populations over the last 200,000 years was, I suspect, a cultural phenomenon; we already had the brains.

10: HUMAN CULTURE EVOLVES PROGRESSIVELY

Three major advances have propelled human dominion ever forward. The first was becoming bipedal and erect, freeing our front limbs to carry, craft, and gesture. No longer needed as support, our hands became more flexible and more versatile. A second step was melding hand signals with our voices to create language, allowing for the rapid exchange of information and shared decision making. Tribal traditions became subject to competition and selection, propelling cultural evolution even more rapidly. The third grand advance in the human trajectory was developing a series of intimate symbioses with a variety of nutritious plants and a few tasty animals. Agriculture, like language, was a social technology that would increase our numbers and advance our dominion. Being able to store food for lean years, humans now flourished in larger settled villages, allowing yet more elaborate cultural innovations. Just as in large insect societies, larger city-states developed specialized castes to perform defined duties; human societies became highly cooperative superorganisms. Living on an older planet, plate tectonics provided concentrated ores, while erosion had amassed deposits of iron ore, coal, oil, and gas. These resources were the foundation for another grand advance—metallurgy. Ever-growing knowledge, together with a more critical analysis of nature, gave rise to the scientific revolution. More recently, we've used fossil fuels to power an industrial revolution, increasingly complex technologies, and ever-more comfortable lives.

COOPERATION AND COMPLEXITY

What are the factors that have given our planet increasingly complex biotas and humans ever-more creative cultures? Energy was the fundamental driver. With oxygenic photosynthesis capturing the energy of sunshine, the living world had a source of continual power. But complex living things break down over time and must reproduce themselves continually to survive in a difficult world. Since reproduction cannot be 100 percent accurate, the replicative process suffers inevitable mutations. These variants, subject to natural selection in changeable environments, have given us an ever-evolving epic of life. Fortunately, there was yet another significant factor.

In a remarkably insightful book, Super Cooperators, mathematical biologist Martin Nowak claims that cooperation “is the third principle force driving progressive evolution” after mutation and selection! In earliest times, he argues, molecular systems that cooperated to gather energy and stabilize their structure prevailed over their non-cooperating neighbors—becoming the “pre-life” from which replicating cells emerged.7 The larger eukaryotic cell, within which a variety of organelles worked in a cooperative manner, proved to be a major advance. These more complex cells gave rise to multicellular organisms, within which thousands to trillions of cells work in tightly regulated unison. Finally, a few animal species have taken social cooperation to a level where a society of individuals acts as if were a single integrated assemblage: a superorganism. Army ants, honeybee colonies, and human societies are examples.

Comparing various cooperative versus selfish strategies in extended computer simulations, Nowak elucidates the origin and maintenance of altruism within both insect and human societies. He argues that cooperation was foundational to our premier talent: language. The advantage of better communication between individuals was especially significant as they challenged other groups for access to limited resources. Nowak's studies make clear that within-group cooperation in an environment of inter-group competition has been central to making us the dominant species on the planet. Today, cooperation is epitomized by multinational teams of scientists exploring subjects ranging from the Higg's Boson to cancer and cosmology. Working together to produce more food and confront our diseases, we have propelled our numbers into the billions.

THE HOLOCENE HAS BECOME THE ANTHROPOCENE

Empirically, we humans have extended ourselves across and into every ecological niche on the planet, making it impossible to say anymore where humans end and nature begins.

—Paul Wapner8

Over the last 2.6 million years, planet Earth witnessed a series of ice ages geologists defined as the Pleistocene epoch. This was arbitrarily terminated by the beginning of the Holocene, about 11,700 years ago. Nowadays, scholars of many persuasions are using the name Anthropocene in place of Holocene. And why not? We “anthropoids” have created a new epoch! In fact, 11,700 years ago is close to the time when elegant stone spear points—the Clovis tradition—first appeared in the archaeological record of North America; this is exactly the time when many of the New World's larger mammals began to disappear. Surely, this is reason enough to dump the Holocene and replace it with Anthropocene.

Nevertheless, human numbers did not expand significantly until we initiated animal and plant domestication, beginning 10,000 years ago. Alongside reliable rivers, hydraulic agriculture could now support thousands of our kind. With stable agricultural communities in place, human cultural creativity found new ways for us to expand our knowledge and our skills. Greek civilization promoted literature, science, and mathematics. Islamic scholars gathered, translated, and expanded scientific understanding. From India came a numbering system that empowered mathematics; from China came the compass, gunpowder, paper, and printing. Spurred on by aggressive mercantilism, inspired by an evangelical religion, and empowered by advanced weaponry, Europeans began a global hegemony. Coupling scientific inquiry and technological innovation with the latent energy of fossil fuels, the scientific and industrial revolutions have accelerated technological elaboration ever more rapidly. “Consecutively progressive,” both science and technology have allowed us to better understand the world in which we live, constrain our diseases, nourish ourselves more generously, and increase our numbers explosively.

Various scholars begin the “Anthropocene” with agricultural expansion or early civilizations in Egypt and Mesopotamia. Others begin with the Industrial Revolution, or the use of atomic bombs in Japan. In her book Adventures in the Anthropocene, Gaia Vince begins the Anthropocene with the end of World War II, using the Holocene as a contrast to the extraordinary changes that have afflicted our home planet over these last seventy years. Replete with extensive research and a wealth of data, the author is optimistic, writing, “The Anthropocene could become a time of more nuanced climate change, where temperature and precipitation are modulated to humanity's needs. Where weather is planned. It's an extraordinary idea.”9 (Not extraordinary, utterly unrealistic in my view.) Nevertheless, and regardless of how we define it, the Anthropocene is like nothing that has ever come before!

Continuing human advances, together with our growing numbers, have given rise to one of the most disruptive episodes in the long history of life. Thousands of millions of years were required for the earliest forms of life to elaborate themselves. The evolution of complex animals and a terrestrial flora took place over many millions of years. In bold contrast, and in less than ten thousand years, a bipedal primate has become a species that commandeers over half of the world's terrestrial ecosystems, burns ever more fossil fuel, fills the air with electromagnetic information, and investigates the cosmos by studying the light from distant stars. In fact, in 2014, we blasted flat a high mountain top in Chile to build yet another huge telescope! (The scientific-industrial complex has no intention of curbing its appetite.) Emblematic of our culture, modern societies show no inclination to slow their relentless transformation of the globe. The continuing advance of human technologies and the explosive expansion of our numbers bring us to our final chapter.