The Five-Million-Year Odyssey

The Human Journey from Ape to Agriculture

Peter Bellwood

• Publisher: Princeton University Press
• Year: 2022
• ISBN:
  9780691236339
• Topic: Biological Sciences
• Subtopic: Evolution
• Index: Biological Sciences

The epic story of human evolution, from our primate beginnings more than five million years ago to the agricultural era Over the course of five million years, our primate ancestors evolved from a modest population of sub-Saharan apes into the globally dominant species Homo sapiens. Along the way, humans became incredibly diverse in appearance, language, and culture. How did all of this happen? In The Five-Million-Year Odyssey, Peter Bellwood synthesizes research from archaeology, biology, anthropology, and linguistics to immerse us in the saga of human evolution, from the earliest traces of our hominin forebears in Africa, through waves of human expansion across the continents, and to the rise of agriculture and explosive demographic growth around the world.Bellwood presents our modern diversity as a product of both evolution, which led to the emergence of the genus Homo approximately 2.5 million years ago, and migration, which carried humans into new environments. He introduces us to the ancient hominins—including the australopithecines, Homo erectus, the Neanderthals, and others—before turning to the appearance of Homo sapiens circa 300, 000 years ago and subsequent human movement into Eurasia, Australia, and the Americas. Bellwood then explores the invention of agriculture, which enabled farmers to disperse to new territories over the last 10, 000 years, facilitating the spread of language families and cultural practices. The outcome is now apparent in our vast array of contemporary ethnicities, linguistic systems, and customs.The fascinating origin story of our varied human existence, The Five-Million-Year Odyssey underscores the importance of recognizing our shared genetic heritage to appreciate what makes us so diverse.

1

The Odyssey Revealed

Five Million Years of Hominin Achievement

During the past five million years, humans and their hominin ancestors have evolved from a bipedal (two-legged) ape into the globally dominant species that we call Homo sapiens. We are now eight billion people rather than a few thousand; mobile phones rather than stone tools dominate the lives of many of those billions; and, by the start of the Colonial Era (1492 CE), our ancestors spoke at least 8,000 different languages, of which about 6,500 survive today. Our evolution has taken us from an African ape, through many intermediate hominin species, to Homo sapiens and the dizzying heights of the modern technological revolution. Indeed, the success of our global domination is currently causing many of us great concern.

How did all of this happen? The events of the past five (or more) million years have been immense in detail, and much of that detail will forever be lost to us. But there are guiding threads. Two essential processes, evolution and migration, have underpinned the histories of all species of life on earth, from viruses to whales, including Homo sapiens and its ancestors. Evolution creates new species out of existing ones, and migration carries the members of those new species into new environmental conditions, thus encouraging evolution to continue in new directions.

The never-ceasing production lines created by evolution, migration, and further evolution have left continuous traces of their passage, silent witnesses scattered through space and time waiting patiently for those who can find and interpret them. Those traces are the plot for a saga on a cosmic scale.

The traces are not only biological; they include two major nonbiological categories of human achievement, these being the archaeological cultures that record ancient human lifestyles and the families of related languages that record how humans communicated in the past. Our cultures and languages evolved and traveled with their human creators to far-flung corners of the world during the course of prehistory. Together with the fossils and the genes, they add to the basic conceptual scaffold around which this book is constructed.

The human Odyssey, from ape to agriculture, is thus our main field of concern. I will examine how the different hominin populations that have existed during the past five million years, including our own modern human species and its immediate ancestors, have been identified by paleoanthropologists, archaeologists, and geneticists. One ultimate goal is to show how these ancestral populations have contributed to the creation of our own place in the world, although it is not my intention to put Homo sapiens on a pedestal of ultimate perfection. Many might say that we deserve no such accolade.

However, we might still ask: Where does Homo sapiens actually fit within the Odyssey? We did not exist five million years ago as a recognizable species separate from other hominins, except perhaps in nascent form; we were an undifferentiated glimmer in the genetic cosmos of archaic humanity, waiting for the eventual chance to make an appearance and then migrate into the world to become a new species. I describe the details, such as they are known to us, of this appearance later, but the main point to be stressed in this introduction is that we are a very young species compared with the five-million-year hominin Odyssey as a whole. The oldest fossil skulls recognized as approaching a modern human status in terms of brain size and shape are only about 300,000 years old. All of us alive today descend from a common genetic ancestry of similar antiquity, at least in terms of DNA comparisons between the living human populations of the world.

Yet the genus Homo, within which Homo sapiens is the sole survivor of what were once several species, including Homo erectus and the Neanderthals (Homo neanderthalensis), has existed for at least two million years, and hominins in general for more than five million years. This recency for Homo sapiens as a distinct species means that we can interbreed freely, if age and health permit, with a partner from anywhere in the world. The differences we perceive in individual bodily characteristics, such as skin or hair color, are superficial.

Furthermore, the recency of our origin in Sub-Saharan Africa means that all living humans carry the same basic ability to create languages, cultures, and societies at a global level of complexity that has been recorded by linguists, historians, anthropologists, and ethnographers for well over a century. We can each learn, speak, and understand the language of anyone else in the world, if we wish to. The shared features of basic behavior and intelligence that we see across the human population today must also have characterized our ancestors since the African emergence and expansion of our species throughout the Old World, from South Africa to Australia, by at least 50,000 years ago.

Right now, therefore, humans across the whole world are a biological unity at the species level. However, it was not always so. Before the main spread of Homo sapiens out of Africa, many different hominin species roamed the Old World continents at any one time. There were even several distinct hominin genera (groups of related species) in Africa before one million years ago. These genera and species had been differentiating from each other for many times longer than the modern human time span, so they expressed far more diversity than we see across our own species now. All eventually became extinct, except for the still rather obscure line of genetic descent that led eventually to us, Homo sapiens. Some of those pre-sapiens species, especially the Neanderthals and Denisovans of Europe and Asia (to be discussed in chapter 4), also hybridized with our own Homo sapiens ancestors, in the process transferring genes that still survive among us today.

From a five-million-year perspective, one point cannot be denied. As Homo sapiens, we have ridden hard on the achievements of our remote ancestors to become the most successful, and now unique, heirs to those five million years of hominin biological and cultural evolution. As Charles Darwin noted over 150 years ago, “Man still bears in his bodily frame the indelible stamp of his lowly origin.”¹ That five-million-year time span postdates our evolutionary separation from the ancestors of the living great apes, especially the panins (chimpanzees and bonobos, members of the genus Pan) of equatorial Africa.² After that separation, hominins forged their own unique identities as upright bipedal and increasingly large-brained primate life-forms. The panins forged their own identities in another direction to become the knuckle-walking chimpanzees and bonobos that exist in tropical Africa today.

We come from an ape heritage, as of course do our closest cousins in the natural world, the great apes themselves. Jared Diamond once referred to us as the “Third Chimpanzee,”³ but our brains are huge by ape standards, and our cultural creations astonishing. Our ancestors spread eventually across the whole world, while those of the living great apes (panins, gorillas, orangutans) remained in tropical Africa and Southeast Asia, where they suffer threatened conditions of survival today. Our current human population numbers cause many of us concern, as does our ongoing impact on Planet Earth. In evolutionary terms we have been enormously successful, at least so far.

Brains, Cultural Creations, and Population Numbers

Let me illustrate the overall evolutionary success of humans with an impressionistic illustration of two aspects of the hominin achievement plotted against time. The first is the increase in the volume of the brain, from a chimpanzee (average 380 cubic centimeters) to a modern human (average 1,350 cubic centimeters), as recorded from fossils during the last 3.5 million years for which such brain size records exist (figure 1.1). A brain volume increase on this scale—by a factor of three or four through such a relatively brief period of evolutionary time—is unprecedented in the rest of the mammalian world.

The second aspect lies in human behavior, in the rising complexity of cultures and societies. Figure 1.2 is schematic and selective, but it focuses on some of the major developments in social and economic organization as recognized in the record of archaeology. These include developments in technology (e.g., stone to metal), provision of food (e.g., hunting and gathering to food production), and social organization from small nuclear family groups to the state-level empires of early history. The increasing tempo of development with the rise of food production after 10,000 years ago is evident.

Figure 1.1. The evolution of hominin brain volume (cubic capacity) through time. A = Homo antecessor; E = Homo erectus; H = Homo heidelbergensis; S = Sima de los Huesos (Spain) average. Data partially from Dean Falk, “Hominin brain evolution,” in S. Reynolds and A. Gallagher, eds., African Genesis (Cambridge University Press, 2012), 145–162.

Figure 1.2. The evolution of hominin culture since 3.5 million years ago, with a time line for the four acts described in this chapter. Act I commenced six million years ago, but its early phases reveal no definite signs of cultural activity. The figure has two registers and starts at the bottom left. Note the changes in chronological scale in the vertical axes. KYA = thousands of years ago; MYA = millions of years ago.

There is a third aspect of the human career that is more difficult to illustrate: the increase in the estimated size of the human population. Prehistoric population sizes can be inferred from indirect sources of information, such as comparable ethnographic population densities, and areas and numbers of archaeological sites at different points in time. They can also be estimated from genetic comparisons of mutation frequency between the DNA sequences of different ancient and living populations. The larger the population, the more frequently one might expect mutation events to have occurred in its genome, and such mutation events can be dated using molecular clocks. However, I do not attempt here to create a graphical guestimate of hominin population numbers through time because there are too many uncertainties. The key point is that our numbers have grown dramatically during the course of our Odyssey.

The oldest hominin populations were small, and there were perhaps still fewer than two million humans in the world at 12,000 years ago. With the widespread establishment of food production, starting around 12,000 years ago, human populations began to increase with unprecedented speed. By 2,000 years ago we had reached an estimated 300 million people worldwide. Since 1 CE our numbers have skyrocketed, to one billion by 1800 CE and to almost eight billion now.

Of course, the trends through time in these three examples of human achievement are not identical. Our modern human brain volume was achieved by some hominin species more than 50,000 years ago, including our own Homo sapiens ancestors and our extinct Neanderthal cousins. There was a major development of cultural complexity (e.g., art, body ornamentation, and purposeful burial of the dead) at about the same time. But our population size only really began to explode with the beginnings of agriculture after 12,000 years ago. States, cities, and writing only became prominent in certain regions of the world after about 5,000 years ago. Before this, most of humanity lived in small egalitarian kinship-based communities.

In short, our evolution over the past five million years of our Odyssey has impacted our world on a scale equivalent to that of a major epochal change, like the coming of the Ice Ages or the appearance of mammals. As earth scientists Simon Lewis and Mark Maslin point out, for the first time in the earth’s 4.5-billion-year history, a single species is increasingly dictating its future.⁴

Hominin Evolution as a Four-Act Drama

The events that have taken place in hominin prehistory can be visualized as a sequence of four Acts, which can be succinctly described as follows (figure 1.2):

• Act I: hominins before the genus Homo (6 to 2.5 million years ago).

• Act II: the genus Homo onward to the fossil appearance of Homo sapiens (2.5 million to 300,000 years ago).

• Act III: Homo sapiens onward to the appearance of food production (300,000 to 12,000 years ago).

• Act IV: the age of food production (12,000 years ago to the present).

Act I (discussed in chapter 2) was played out in Africa by the hominins who existed after the split from the panins but before the appearance of the genus Homo (to which we all belong today). It featur...