Big History—Humans in the Cosmos

Big History—Humans in the Cosmos

Lecture 48

Agriculture appeared about 10,000 or 11,000 years ago. Before the appearance of agriculture, all human beings were foragers.

If asked (perhaps around a camp re) to explain how everything got to be the way it is, how might we respond? Let’s begin with human history. We live in the largest and most complex human community ever created. Six billion humans, often in con ict with each other, are linked through trade, travel, and modern forms of communications into a single global community. This community was created in just a few hundred years. About 300 years ago, human beings crossed a sort of threshold as human societies became more interconnected and began to innovate faster than ever before. For 5,000 years before this, most people had lived in the large, powerful communities we call “Agrarian civilizations.” They had cities with magni cent architecture and powerful rulers sustained by large populations of peasants who produced most of society’s resources. Innovation was slower, so history moved more slowly, and there were fewer people than today. Two thousand years ago, there were about 250 million people on Earth.

The rst Agrarian civilizations appeared in regions such as Mesopotamia, Egypt, and China. During the previous 5,000 years, humans had increasingly lived in small peasant villages governed by local chiefs. Yet many still lived by foraging, gathering what they needed as they migrated through their home territories. The appearance of agriculture, just over 10,000 years ago, counts as a fundamental historical threshold because agriculture increased the amount of resources humans could extract from a given area. By doing so, it stimulated population growth and innovation and laid the foundations for the rst Agrarian civilizations.

In the preceding 200,000 to 300,000 years, all humans had lived as foragers, in nomadic, family-sized communities. Slowly, they spread through Africa and around the world. For most of this time, humans were only slightly more numerous than our close relatives, the great apes, are today. Our species, Homo sapiens, appeared about 200,000 to 300,000 years ago somewhere in

Africa. What made them different from all other animals, and enabled them to explore so many different environments, was their remarkable ability to exchange and store information about their environments. Humans could talk to each other, they could tell stories, and unlike any other animals, they could ask about the meaning of existence! Their appearance counts as a fundamental threshold in our story.

To understand how the rst humans appeared, we must survey the history of life on Earth. Like all other species, our ancestors evolved by natural selection. They evolved from intelligent, bipedal, ape-like ancestors known as “hominines” that had appeared about 6 million years earlier. The hominines were descended from primates: tree-dwelling mammals with large brains and dexterous hands that had rst appeared about 65 million years ago.

The mammals were furry, warm-blooded animals that had rst evolved about 250 million years ago. They were descended from large creatures with backbones, whose ancestors had left the seas to live on the land about 400 million years ago. These were descended from the rst multicelled organisms, which appeared about 600 million years ago in the Cambrian era.

During the preceding 3 billion years, all living organisms on Earth were single-celled. The rst living organisms had appeared by about 3.8 billion years ago, just 700 million years after the formation of our Earth. They were the ancestors of all living creatures on today’s Earth. The speed with which they appeared suggests that life is likely to appear wherever there are planets bathed in the light and energy of nearby stars but far enough away for liquid water to form. The appearance of life is one of the most important thresholds in the big history story.

Life could evolve only after the crossing of three earlier thresholds: the creation of planets, stars, and chemical elements. Our Earth was formed about 4.5 billion years ago, along with all the other planets, moons, and asteroids and comets of our solar system, from the debris formed as our Sun was created. Solar systems probably formed countless billions of times in the history of the Universe.

Our planet, like the living organisms that inhabit it, is made up of many different chemical elements, so neither could have formed if the chemical elements had not been manufactured in the violent death throes of large stars (in supernovae) or in the last dying days of other stars. The earliest stars may have died within a billion years of the creation of the Universe. Since then, billions upon billions of stars have died and scattered new elements into interstellar space. The rst stars were born, like our Sun, from collapsing clouds of gas within about 200 million years of the big bang. Today, there may be more stars than there are grains of sand on all the beaches and deserts of our Earth. And that takes us back to the beginning. Our Universe began as a tiny, hot, expanding ball of something popped out of nothingness like an explosion about 13.7 billion years Trying to imagine the long, ago. The explosion has continued ever drawn-out death of our since, and we are part of the debris it has created. Universe suggests that we

may live in the most exciting

The story told in this course is our best era of the Universe’s history. shot at explaining origins of all kinds. Like all origin stories, it is far from perfect and will change in the future. Important details, including the date of the big bang, have been clari ed in the last decade or two. Here are some other possible areas in which the story may change. Cosmologists will keep pushing back their understanding of the origins of the Universe. The holy grail will be a theory explaining why the Universe popped out of nothing, or perhaps what it popped out of. Cosmologists will try to understand “dark matter” and “dark energy.” Biologists will acquire a better understanding of the origins of life on Earth (and perhaps elsewhere). Anthropologists will seek new evidence on the origins of our species. To do this they will have to invest more time and energy in the archaeology of Africa in the Paleolithic period and improve their understanding of the evolution of symbolic language and collective learning. Genetic dating techniques will allow us to track human migrations with much greater precision. We also need an improved interdisciplinary understanding of complexity that can illuminate our understanding both of stars and of modern human societies and can tease out the many links between different types of complexity.

Despite the limitations of any account of big history, the story is one we need to know and tell. Telling it backward is a good way of showing how such stories can help us map ourselves onto the cosmos. We see how the modern world ts into the larger story of human history, how human history ts into the history of life on Earth, and how these stories t into the largest story of all—that of the Universe as a whole. Like the different parts of a Russian matryoshka doll, each story is nested in and helps explain the stories surrounding it. This sort of “mapping” is closely linked to our sense of meaning. Scientists are usually reluctant to discuss meanings and prefer to concentrate on getting the story right. But as symbolic beings, most of us have to look for meaning in any universal story. So what meanings may be hidden within big history?

The suggestions that follow are personal answers prompted by teaching big history for almost 20 years. Trying to imagine the long, drawn-out death of our Universe suggests that we may live in the most exciting era of the Universe’s history: its springtime, when there existed the perfect balance of energy and space to make complex things such as ourselves. We have also seen that the societies we live in today may represent the most complex structures in our part of the galaxy. Can our Universe create more complex structures? Either way, our extraordinary complexity makes us rather interesting!

We are also the only creatures we know of that are capable of seeking meaning and purpose in the Universe. In the scienti c view of the Universe, in which there is no deity or conscious creator, that means that we become the Universe’s bearers of purpose and meaning. It is, after all, awe-inspiring to think that blind algorithmic processes might have successfully created an organism clever enough to gure out how those blind algorithmic processes created an entire Universe!

And that’s where we’ll end! I hope you have enjoyed this telling of our modern creation story, and I hope you will want to encourage others to become acquainted with it. If they are young enough, they may be the ones who will help construct a new and perhaps better story in the future.

Essential Reading

Supplementary Reading

Questions to Consider

Christian, Maps of Time, 497–99 (a brief synopsis of the modern creation story).

Christian, “World History in Context.”

1. What do you regard as the most important themes of the modern creation story?

2. Does the modern creation story carry ethical baggage like all earlier creation stories?