1.2 Early Human Evolution & Migration

Human Evolution

The concept of evolution over time is one we are all likely familiar with. Consider, for example, how technology has evolved. The first true smartphones appeared on the market at the beginning of this century, but these complicated devices didn’t spring all at once from the minds of ambitious engineers. Rather, these engineers built on technology that had evolved and improved over many decades. In the mid-1800s, telegraph technology first demonstrated that electricity could be used for long-distance communication. That technology paved the way for the first telephones, which were basic and expensive but over many decades became more sophisticated, more common, and cheaper. By the early 1980s, electronics companies had begun selling telephones that used radio technology to communicate wirelessly. Over time these devices were made faster and smaller, and companies added features like cameras, microprocessors, and eventually internet access. With these evolutionary transformations, the smartphone was born.

Figure 2.3: Lucy. Despite the incomplete state of the remains of Lucy, a member of the ancient genus Australopithecus, the similarities between her and modern humans of the genus Homo are striking. This image is a photoshopped reproduction of her skeleton. (credit: modification of work “Reconstruction of the fossil skeleton of “Lucy” the Australopithecus afarensis” by “120”/Wikimedia Commons, CC BY 2.5)

Possibly the earliest member of the genus Homo was Homo habilis. This species appears in the archaeological record about two to three million years ago. Habilis means “handy”; it was thought at one time that this was the first species to have created stone tools. We now know that stone tools predate Homo habilis, but the name has stuck. Homo habilis resembles us in many ways, with a large brain similar to ours as well as small teeth and a face we might recognize as human. But members of the species also had many ape-like characteristics, such as long arms, hairy bodies, and adult heights of only three or four feet.

Figure 2.4: Homo Habilis. Partially restored remains, like the skull represented by this replica, are some of the most important evidence we have of the human ancestor Homo habilis. (credit: “Skull of Homo Habilis (Replica)” by “Luna04”/Wikimedia Commons, CC BY 2.5)

Around two million years ago, a species even more similar to us, Homo erectus, emerged in East Africa. It likely evolved from Homo habilis. As the name erectus for “upright” suggests, this species lived entirely on the ground and walked—even ran—exclusively in an upright position. The consequences of this evolutionary shift were huge. Being upright meant that the body’s digestive organs were pulled down lower and into a smaller space. That in turn necessitated a change in diet, away from tough plants and toward easier-to-digest items like nuts, fruits, tubers, honey, and even meat. Living on the ground was also more dangerous because it made eluding predators more difficult. However, the upright position left Homo erectus’s hands free to use tools. This advantage likely led to further evolutions that made human hands more dexterous over time, prompting the wider adoption of ever more sophisticated tools.

Members of Homo erectus shared other close similarities with modern humans. They were about the same height as we are, sometimes reaching just over six feet. They made and used relatively sophisticated stone tools and relied on fire for both warmth and cooking food. They likely constructed huts of wood and fur in which to live and worked cooperatively with each other to hunt and forage. The position of the larynx in the throat also suggests that Homo erectus may have had some capacity to communicate vocally, which would have aided in cooperative endeavors. Finally, archaeologists have uncovered strong evidence that Homo erectus cared for the sick and elderly. This evidence includes the discovery of the remains of individuals who suffered from debilitating diseases yet lived a long time, indicating that assistance was both necessary and provided by others. Together these characteristics made the species highly adaptable to changing climates and environments, helping explain why its members survived for so long. Homo erectus populations lived until as recently as about 100,000 years ago.

Sometime between 1.8 and 1.5 million years ago, Homo erectus started migrating into other parts of Africa and beyond, reaching North Africa, the Near East, Europe, and East and South Asia over hundreds of thousands of years. The reasons for this extensive migration are still debated, but they likely included climate change and the desire to follow certain types of prey. Homo erectus appears to have stayed close to rivers and lakes during migration, hunting and eating animals like rhinoceroses, bears, pigs, and crocodiles, as discoveries in the Near East have confirmed. Populations evolved to adapt to the different environmental conditions into which they moved. Over time this led to a diversity of human species, including Homo heidelbergensis; Homo neanderthalensis, or Neanderthals; Denisovans; and modern humans, or Homo sapiens (sapiens means “wise”). Some of these species, like Denisovans and Neanderthals, emerged outside Africa. Others, like Homo heidelbergensis and Homo sapiens, emerged in Africa first and later migrated to other areas.

The extent to which these different human species interacted with each other remains unclear. DNA evidence from a bone found in Siberia has shown that a girl (who died at age thirteen) was born there of a Denisovan father and a Neanderthal mother. Another recent study demonstrated that modern European and Middle Eastern populations have between 1 and 4 percent Neanderthal DNA. This appears to suggest that mating between Homo sapiens and Neanderthals was quite common. The careful work of archaeologists and other scholars has also made clear that some species evolved from others. For example, both Neanderthals and Denisovans appear to have evolved from populations of Homo heidelbergensis.

At some point between forty thousand and fifteen thousand years ago, the diversity of human species declined and only Homo sapiens remained. Two models attempt to explain why. The first and most commonly accepted is the “out of Africa” model. This theory suggests that modern humans emerged first in Africa approximately 200,000 years ago and then, approximately 100,000 years ago, expanded out of Africa and replaced all other human species. The second model is often called the “multiregional evolution model” and proposes that Homo sapiens evolved from Homo erectus in several places around the same time. This model emerged as an explanation for the great diversity of modern human traits in different populations around the world. But it relies primarily on the study of fossils and archaeological records rather than on genetic data.

These theories about human evolution are not necessarily mutually exclusive, and the real answer to the puzzle may be a combination of the two. For example, it’s entirely possible that modern humans or a common ancestor did emerge first in Africa. Then, as this species expanded around the world, it mixed its genetic information with that of other human species. The DNA evidence collected in recent years certainly suggests a more complicated picture, and the debate has not yet been settled. The tools of both archaeology and molecular genetics continue to reveal new insights into the puzzle of human evolution and the rise of Homo sapiens. And the conclusions we can draw about our distant past will continue to change as we learn more.

Dueling Voices

What Happened to Neanderthals in Europe?

For tens of thousands of years before Homo sapiens arrived in Europe, the continent was home to Neanderthals. Then, about forty thousand years ago, right around the time modern humans entered Europe, the species neanderthalensis began to rapidly die out. For more than a century and a half, scholars have been trying to understand why.

Figure 2.5: An Imagined Neanderthal Woman. This modern reconstruction of what a Neanderthal woman may have looked like demonstrates a striking resemblance to modern humans. (credit: “Reconstruction of Neanderthal woman (makeup by Morten Jacobsen)” by Public Library of Science/Wikimedia Commons, CC BY 2.5)

One theory is that modern humans replaced the Neanderthals in Europe through violent competition, including a type of warfare between the two groups. Another model argues that the competition was less about violence and more about resources. This theory posits that modern humans were simply better tool makers, had better survival strategies, and possibly experienced lower mortality rates and higher birth rates. Neanderthals simply couldn’t keep up, and their small population dwindled and then disappeared entirely.

Modern DNA analysis has opened the door for a new theory, that mating occurred between the two species and that the population of Neanderthals was simply absorbed by modern humans. The presence of small amounts of Neanderthal DNA in modern human populations lends some credibility to this idea, but it seems unlikely to explain the total disappearance of Neanderthals.

Finally, analysis of climate change in Europe has revealed some variations that could have weakened Neanderthal populations and led to their disappearance in some areas. As of now, no one theory can account for everything. It seems possible that several factors were at play rather than a single primary cause, so the debate goes on.

• How might more than one of these reasons, or all of them, have contributed to the decline of Neanderthals in Europe?
• Can you think of any other explanations for the extinction of Neanderthals?

Why Did Humans Move and Where Did They Go?

Archeological evidence indicates that Homo sapiens began migrating out of eastern and southern Africa as early as 200,000 years ago. This expansion took early humans deeper south, west, and north as far as the Mediterranean Sea. Approximately 100,000 years ago, groups of Homo sapiens left the African continent and began a global migration that lasted for tens of thousands of years. After crossing the Sinai into southwest Asia, early migrants out of Africa likely followed the coasts of Asia, and by about seventy thousand years ago, they had made their way into India and China.

Figure 2.6: Migration of the Earliest Humans. Homo sapiens first expanded around south and eastern Africa before embarking on migrations that eventually took them around the world. (credit: modification of work “Spreading of Homo sapiens” by “NordNordWest”/Wikimedia Commons, Public Domain)

Some groups continued moving south through Malaysia, into Indonesia and beyond. In places like Papua New Guinea and Australia, there is evidence of settlements at least forty-five thousand years old. Others groups making their way into southwest Asia from northern Africa entered Europe around forty thousand years ago, moving either along the Mediterranean coast or by way of Turkey into the Danube valley. By twenty-five thousand years ago, Homo sapiens had reached Siberia and other parts of northern Asia. And approximately fifteen thousand years ago, some groups in Asia crossed into North America, eventually reaching the tip of South America and settling at various locations in between.

This timeline has been pieced together based on the analysis of several archaeological finds. But our knowledge is still limited, and new discoveries frequently require adjustments to the proposed dates and patterns of global human migration. For example, we now know that because the Earth was in its most recent ice age during this period, areas currently covered by water were then dry land. This is true for large portions of maritime Southeast Asia as well as the Bering Strait between Asia and North America. Humans were able to walk as far south as Java and from Asia into Alaska.

Yet they also roamed as far as Australia, which was not connected by land to Asia in this period. This means they must have used rafts of some type, probably by crossing short distances between islands. Likewise, discoveries of human habitation dating from fourteen thousand years ago in South America suggest that rafts or boats of some kind may also have been used to skirt the North and South American coasts. No crafts have been or may ever be found, but we must assume they existed.

More interesting still, analysis of the remains of the eight-thousand-year-old Kennewick Man discovered in 1996 in Washington State reveals anatomical features more consistent with Southeast Asian populations than with those traditionally assumed to have populated the Americas. This discovery complicates the version of human migration we think we know, and if anything, it suggests there is much about the process that we may never fully understand.

But what triggered this migration in the first place? Despite the uncertainties, we can draw some speculative conclusions. We know that around the same time Homo sapiens began leaving Africa, the climate there was becoming increasingly dry. Drier conditions meant fewer of the plants and animals humans needed to survive were available. Modern humans were hunter-gatherers like their evolutionary ancestors, meaning they survived by employing the strategies of hunting animals and gathering wild plants rather than by planting crops and raising livestock. As hunter-gathering societies regularly forage over a large area, any scarcity of resources in some places or abundance in others encourages movement. In the lifetime of a single individual, a large-scale migration would have been barely perceptible, if at all. But over tens of thousands of years, human populations traversed an enormous portion of the globe. Nor did they go in a single direction or all at once. Groups likely moved back and forth over areas, responding to the climatic conditions and availability of resources. There were long periods of relative stasis punctuated by movement, creating waves of migration in various directions.

As humans moved into new environments, they adjusted their strategies to be successful under new conditions. This meant learning to gather different types of plants and hunt different types of animals they came into contact with, including mastodons, woolly mammoths and rhinos, various types of grazing animals, and giant sloths and beavers. The arrival of humans who were highly effective at survival occasionally accompanied major transformations in their new environments. Scientists who study now-extinct animals have recognized for some time that human hunting likely contributed to the decline of a number of these species. Before humans arrived approximately forty-five thousand years ago, for example, Australia was home to a number of large reptiles, a marsupial lion (which carried its young in a pouch), and huge wombats and kangaroos. These species began to vanish around the same time humans reached Australia and well before the climatic warming that led to the extinction of large animals in other places.

Figure 2.7: A Marsupial Lion. Tens of thousands of years ago, Australia was home to many large marsupials, such as this marsupial lion. Its fossilized skeleton is shown here in the Victoria Fossil Cave where it was found. (credit: “A skeleton of a Marsupial Lion (Thylacoleo carnifex) in the Victoria Fossil Cave, Naracoorte Caves National Park” by “Karora”/Wikimedia Commons, Public Domain)

Early Human Technologies

To understand how early humans lived hundreds of thousands and even millions of years ago, scholars use the tools of archaeology to analyze the objects left behind. Many were made of materials like wood, animal skin, and earth, which rarely endure in the archaeological record. Bone items are somewhat more durable and have occasionally survived. But our window into the distant past is quite small. Stone items are the most likely to have lasted long enough for us to study them today. Beginning possibly as early as 3.3 million years ago, our distant pre-human ancestors began using stone tools for a variety of purposes. This event marks the start of the Paleolithic Age (lithos means “stone”), which lasted until nearly twelve thousand years ago.

The earliest known human-made stone tools date from about 2.6 million years ago. They were likely first created by Homo habilis, by smashing smooth rocks together to create crudely sharpened edges. The resulting implements are often described as Oldowan tools, and their use continued until about 1.7 million years ago. While a seemingly simple adaptation from our perspective, the development of Oldowan tools in fact represents a huge leap in human engineering ability. These sharpened stones served a variety of cutting, scraping, and chopping purposes. They were highly efficient tools for killing animals, butchering meat, smashing bones to access marrow, and a host of similar tasks.

Beginning around 1.7 million years ago, some ancient humans began to develop a new and more sophisticated style of stone tool by carefully chipping away smaller flakes of the stone core to create a teardrop-shaped implement often described as a hand-axe. Far thinner and sharper than the Oldowan tools, hand-axes were even better at the cutting, scraping, and chopping tasks for which they were designed. They were such an improvement over earlier tools that archaeologists have given them their own name. They are called Acheulean tools (pronounced ah-SHOOL-ee-an), after Saint-Acheul, the site in France where they were first found in the nineteenth century CE. Since then, more Acheulean tools have been uncovered in Africa, the Middle East, and India and scattered in parts of East Asia.

Figure 2.8: Early Paleolithic Stone Tools. Acheulean hand-axes (a) were far more sophisticated and required more skill to create than the earlier Oldowan variety (b). (credit a: modification of work “Handaxe in quartzite, from the bed TG-10 of Galería in Atapuerca (Burgos, Spain)” by “Locutus Borg”/Wikimedia Commons, Public Domain; credit b: modification of work “Canto tallado de tradición Olduvayense procedente de la región del Sáhara atlántico Guelmim-Es Semara (Museo Arqueológico Nacional de Madrid)” by “Locutus Borg/Wikimedia Commons, Public Domain)

Far superior to the Oldowan variety, Acheulean tools remained the dominant style of stone tool until as recently as about 250,000 years ago. At that time a new type of utensil emerged in Europe, North Africa, and southwestern Asia. Called Mousterian tools, these implements were smaller hand-axes and tools made from stone flakes rather than cores. In older traditions, the flakes had been removed in order to shape the core as desired, such as into a hand-axe. But in the Mousterian tradition, sometimes the flakes were chipped off in such a way that they themselves could be used as small knives for cutting meat, scraping leather, and serving as spearheads attached to shafts. Advances to the Mousterian techniques later led to other tool traditions. By around forty-five thousand years ago, humans were making a great diversity of specialized tools from stone flakes. These included a variety of scrapers as well as engraving tools for carving and carefully reshaping softer materials like bone and antler into either tools or works of art.

Figure 2.9: The Next Generation of Paleolithic Tools. Mousterian stone tools, like these found in Israel, were used as scrapers for more careful butchering of animals between 250,000 and 50,000 years ago. (credit: modification of work “Stone Scrapers for Cleaning & Working Leather, Mousterian Culture” by Gary Todd/Flickr, Public Domain)

Another important tool of our human ancestors was fire. When exactly humans began controlling fire remains a topic of debate. There is evidence that earlier ancestors like Homo erectus used it, but we don’t know whether they were able to start fires or merely used and perpetuated those that naturally occurred. It’s clear, however, that by at least about 125,000 years ago, if not much earlier, modern humans had learned to start and control fires.

Controlled fires were useful for staying warm in cold climates, scaring off predators, and cooking meat to make it easier to consume and digest. Archaeological finds also suggest that controlled fires aided in the manufacture of certain tools. Wooden spears could be hardened in the flame, making them more effective hunting implements. Some types of stone could be treated with heat to make them easier to chip and mold. Fire also played an important social function. Gathering around the heat and light likely aided in bonding and helped build the social connections vital for cooperative activities and group survival.

Sitting around a fire may also have been an occasion for early humans to display one of their most powerful tools, the unique ability to use sounds as language. There is some speculation that earlier human ancestors like Homo erectus were able to make sound and possibly had a type of language. We’ll never know for sure. But we do know that modern humans are capable of making a great variety of different sounds. Biologists calculate that we can produce fifty different phonemes, or distinctive sounds. When strung together in a sophisticated manner, these phonemes can produce many tens of thousands of words to describe what we see, feel, do, and imagine. Beginning at least 100,000 years ago, modern humans began using language in this fashion, gaining a major advantage over competing animals. With language, they could coordinate daily tasks, work much more efficiently in groups, communicate abstract ideas, and pass important information to successive generations. Few tools aided modern humans more than their ability to communicate with complex languages.

While they left no record of their discussions, early humans did leave a number of impressive artistic depictions. The work that has survived includes small animal and human sculptures, usually made of carved bone or stone. The human-shaped items are often of large, possibly pregnant, women and might have served as symbols of fertility. There are also preserved hand prints, created by placing a hand on stone and blowing pigment around it to preserve the image of its shape.

Some of the most stunning prehistoric art still in existence today consists of cave paintings dating as far back as forty thousand years. Many painted caves have been discovered in Spain and France, but there are also examples in England, Italy, Germany, Russia, and Indonesia. The paintings in the Cave of Altamira in northern Spain are prime examples of this type of art. Within the cave, and dating to about thirty-six thousand years ago, are more than two dozen large images of animals including bison, bulls, horses, deer, and boars. Each is painted in impressive detail using combinations of charcoal and ochre (a pigment made from clay) to produce bold reds, yellows, browns, and blacks. In many instances, the artists incorporated features of the cave walls as part of their designs, giving three-dimensional shape and definition to the animals they drew.

Figure 2.10: Paleolithic Art. The Paleolithic artist who painted this (a) bison in Altamira Cave (in what is now Spain) used protruding features of the cave’s surface to create a three-dimensional effect, such as at the bison’s shoulders. (b) Other examples of three-dimensionality in the art of Altamira are apparent in a Czech museum’s model of the cave’s ceiling. (credit a: modification of work “Cave Paintings” by Graeme Churchard/Flickr, CC BY 2.0; credit b: modification of work “A model of the ceiling of Altamira from right, in the Brno museum Anthropos” by “HTO”/Wikimedia Commons, Public Domain)

Beyond the Book

Interpreting Artistic Expression in the Paleolithic Age

We often think of visual art as a relatively modern gesture consisting of works like oil paintings, sculptures, and even computer-designed images. But artistic expression among our species is quite ancient. We may never know how much art was produced tens of thousands of years ago; many examples have probably been lost. But what we do have is fascinating to behold, though interpreting it is much like trying to reconstruct an entire puzzle from just a few pieces.

Some of the most interesting and perplexing artistic works include a number of female images sometimes called Venus figurines. These are relatively small statuettes (one to sixteen inches in height) that were carved from stone, ivory, bone, or clay to resemble women. The tiny Venus of Hohle Fels, discovered in Germany, is the oldest such object found to date. Carved from mammoth ivory, it dates to about forty thousand years ago, and what remains of it depicts a woman with large exaggerated breasts. This feature has led some anthropologists to conclude that it was intended to represent sex, reproduction, or fertility.

Figure 2.11: Venus of Hohle Fels. The Venus of Hohle Fels, found in Germany, was created from mammoth ivory approximately forty thousand years ago and is just under two and a half inches in height. (credit: “Venus”-pendant, mammoth ivory, Alb-Donau Region, on loan from the National Archaeological Museum in Baden-Württemberg, shown at the Landesmuseum Württemberg, Stuttgart, Germany” by “Anagoria”/Wikimedia Commons, CC BY 3.0)

Similar to the Venus of Hohle Fels and also discovered in Germany is the Venus of Willendorf. This female figurine, less than five inches tall, may be as much as thirty-three thousand years old. Like other such images, it shows a woman with exaggerated breasts and a stylized head with no facial features. Analysis of it has produced a number of interpretations, from the traditional representation of fertility to a type of self-portrait.

Figure 2.12: Venus of Willendorf. Those who suggest the Venus of Willendorf may be a self-portrait note that it could be showing how a woman would have seen herself if she were looking down instead of at her reflection. (credit: “Venus von Willendorf; Kopie” by “Thirunavukkarasye-Raveendran”/Wikimedia Commons, CC0 1.0)

Unlike the preceding examples, the Venus of Dolní Věstonice, discovered in the modern Czech Republic, is made of ceramic. It stands just under four and a half inches tall and may be as much as twenty-nine thousand years old.

Figure 2.13: Venus of Dolní Věstonice. The small Venus of Dolní Věstonice is an early example of a fired-clay sculpture. (credit: modification of work “Dolní Věstonice Venus – Fossils in the Arppeanum” by “Daderot”/Wikimedia Commons, CC0 1.0)

Various other female figurines have been found as far from Europe as central Russia, and while individually unique, all have the same characteristics. They are small and were likely intended to be portable. They have exaggerated breasts and often show reproductive organs. They have large bellies that may reflect pregnancy. But without some record from the people who created them, their true symbolism and use will likely remain a mystery.

• Why do you think these figurines are often interpreted as being related to fertility? Do you think that interpretation is plausible? Why or why not?
• What interpretation of these figurines would you suggest, based on the information you’ve read and seen here?

The significance that cave paintings held for the people who created them may never be fully understood. It was once believed the images were designed to be popularly admired as interesting decorations, not unlike the ornaments we put in our homes today. But given that they are often deep in the dark interiors of the caves, where sunlight could not reach, this interpretation has mostly been abandoned.

With limited insight into the minds of the artists, scholars have concluded that the art likely served some unknown religious purpose. Many speculate that the caves could have been used by shamans—men and women thought to have a special knowledge of the spiritual world—who might have crawled deep into the interior to commune in ceremonies with a type of spiritual force. Such interpretations remain little more than educated guesses. What is indisputable is that the art demonstrates that even tens of thousands of years ago humans had the unique ability to reproduce the world around them in complex, symbolic fashion, through images we can immediately recognize today.