Human Evolution

A

3

The Home Base

Humans have lived as foragers for millions of years. Foragers obtain food when and where it is available over a broad territory. Modern-day foragers (also known as hunter-gatherers)—such as the San people in the Kalahari Desert of southern Africa—also set up central campsites, or home bases, and divide work duties among men and women. Women gather readily available plant and animal foods, while men take on the often less successful task of hunting. Female and male family members and relatives bring together their food to share at their home base. The modern form of the home base—which also serves as a haven for raising children and caring for the sick and elderly—may have first developed with middle Homo after about 1.7 million years ago. However, the first evidence of hearths and shelters—common to all modern home bases—comes from only after 500,000 years ago. Thus, a modern form of social life may not have developed until late in human evolution.

B

Subsistence

Human subsistence refers to the types of food humans eat, the technology used in and methods of obtaining or producing food, and the ways in which social groups or societies organize themselves for getting, making, and distributing food. For millions of years, humans probably fed on-the-go, much as other primates do. The lifestyle associated with this feeding strategy is generally organized around small, family-based social groups that take advantage of different food sources at different times of year.

The early human diet probably resembled that of closely related primate species. The great apes eat mostly plant foods. Many primates also eat easily obtained animal foods such as insects and bird eggs. Among the few primates that hunt, chimpanzees will prey on monkeys and even small gazelles. The first humans probably also had a diet based mostly on plant foods. In addition, they undoubtedly ate some animal foods and might have done some hunting. Human subsistence began to diverge from that of other primates with the production and use of the first stone tools. With this development, the meat and marrow (the inner, fat-rich tissue of bones) of large mammals became a part of the human diet. Thus, with the advent of stone tools, the diet of early humans became distinguished in an important way from that of apes.

Scientists have found broken and butchered fossil bones of antelopes, zebras, and other comparably sized animals at the oldest archaeological sites, which date from about 2.5 million years ago. With the evolution of late Homo, humans began to hunt even the largest animals on Earth, including mastodons and mammoths, members of the elephant family. Agriculture and the domestication of animals arose only in the recent past, with H. sapiens.

---

---

B

1

Models of Subsistence in Early Homo

Paleoanthropologists have debated whether early members of the modern human genus were aggressive hunters, peaceful plant gatherers, or opportunistic scavengers. Many scientists once thought that predation and the eating of meat had strong effects on early human evolution. This hunting hypothesis suggested that early humans in Africa survived particularly arid periods by aggressively hunting animals with primitive stone or bone tools. Supporters of this hypothesis thought that hunting and competition with carnivores powerfully influenced the evolution of human social organization and behavior; toolmaking; anatomy, such as the unique structure of the human hand; and intelligence.

Beginning in the 1960s, studies of apes cast doubt on the hunting hypothesis. Researchers discovered that chimpanzees cooperate in hunts of at least small animals, such as monkeys. Hunting did not, therefore, entirely distinguish early humans from apes, and therefore hunting alone may not have determined the path of early human evolution. Some scientists instead argued in favor of the importance of food-sharing in early human life. According to a food-sharing hypothesis, cooperation and sharing within family groups—instead of aggressive hunting—strongly influenced the path of human evolution.

Scientists once thought that archaeological sites as much as 2 million years old provided evidence to support the food-sharing hypothesis. Some of the oldest archaeological sites were places where humans brought food and stone tools together. Scientists thought that these sites represented home bases, with many of the social features of modern hunter-gatherer campsites, including the sharing of food between pair-bonded males and females.

Critique of the food-sharing hypothesis resulted from more careful study of animal bones from the early archaeological sites. Microscopic analysis of these bones revealed the marks of human tools and carnivore teeth, indicating that both humans and potential predators—such as hyenas, cats, and jackals—were active at these sites. This evidence suggested that what scientists had thought were home bases where early humans shared food were in fact food-processing sites that humans abandoned to predators. Thus, evidence did not clearly support the idea of food-sharing among early humans.

The new research also suggested a different view of early human subsistence—that early humans scavenged meat and bone marrow from dead animals and did little hunting. According to this scavenging hypothesis, early humans opportunistically took parts of animal carcasses left by predators, and then used stone tools to remove marrow from the bones.

Observations that many animals, such as antelope, often die off in the dry season make the scavenging hypothesis quite plausible. Early toolmakers would have had plenty of opportunity to scavenge animal fat and meat during dry times of the year. However, other archaeological studies—and a better appreciation of the importance of hunting among chimpanzees—suggest that the scavenging hypothesis is too narrow. Many scientists now believe that early humans both scavenged and hunted. Evidence of carnivore tooth marks on bones cut by early human toolmakers suggests that the humans scavenged at least the larger of the animals they ate. They also ate a variety of plant foods. Some disagreement remains, however, as to how much early humans relied on hunting, especially the hunting of smaller animals.

B

2

The Rise of Hunting

Scientists debate about when humans first began hunting on a regular basis. For instance, elephant fossils found with tools made by middle Homo once led researchers to the idea that members of this species were hunters of big game. However, the simple association of animal bones and tools at the same site does not necessarily mean that early humans had killed the animals or eaten their meat. Animals may die in many ways, and natural forces can accidentally place fossils next to tools. Recent excavations at Olorgesailie, Kenya, show that H. erectus cut meat from elephant carcasses but do not reveal whether these humans were regular or specialized hunters.

Humans who lived outside of Africa—especially in colder temperate climates—almost certainly needed to eat more meat than their African counterparts. Humans in temperate Eurasia would have had to learn about which plants they could safely eat, and the number of available plant foods would drop significantly during the winter. Still, although scientists have found very few fossils of edible or eaten plants at early human sites, early inhabitants of Europe and Asia probably did eat plant foods in addition to meat.

Sites that provide the clearest evidence of early hunting include Boxgrove, England, where about 500,000 years ago people trapped a great number of large game animals between a watering hole and the side of a cliff and then slaughtered them. At Schöningen, Germany, a site about 400,000 years old, scientists have found wooden spears with sharp ends that were well designed for throwing and probably used in hunting large animals.

Neandertals and other archaic humans seem to have eaten whatever animals were available at a particular time and place. So, for example, in European Neandertal sites, the number of bones of reindeer (a cold-weather animal) and red deer (a warm-weather animal) changed depending on what the climate had been like. Neandertals probably also combined hunting and scavenging to obtain animal protein and fat.

For at least the past 100,000 years, various human groups have eaten foods from the ocean or coast, such as shellfish and some sea mammals and birds. Others began fishing in interior rivers and lakes. Between probably 90,000 and 80,000 years ago people in Katanda, in what is now the Democratic Republic of the Congo, caught large catfish using a set of barbed bone points, the oldest known specialized fishing implements. The oldest stone tips for arrows or spears date from about 50,000 to 40,000 years ago. These technological advances, probably first developed by early modern humans, indicate an expansion in the kinds of foods humans could obtain.

Beginning 40,000 years ago humans began making even more significant advances in hunting dangerous animals and large herds, and in exploiting ocean resources. People cooperated in large hunting expeditions in which they killed great numbers of reindeer, bison, horses, and other animals of the expansive grasslands that existed at that time. In some regions, people became specialists in hunting certain kinds of animals. The familiarity these people had with the animals they hunted appears in sketches and paintings on cave walls, dating from as much as 32,000 years ago. Hunters also used the bones, ivory, and antlers of their prey to create art and beautiful tools. In some areas, such as the central plains of North America that once teemed with a now-extinct type of large bison (Bison occidentalis), hunting may have contributed to the extinction of entire species.

C

Tools

The making and use of tools alone probably did not distinguish early humans from their ape predecessors. Instead, humans made the important breakthrough of using one tool to make another. Specifically, they developed the technique of precisely hitting one stone against another, known as knapping. Stone toolmaking characterized the period sometimes referred to as the Stone Age, which began at least 2.5 million years ago in Africa and lasted until the development of metal tools within the last 7,000 years (at different times in different parts of the world). Although early humans may have made stone tools before 2.5 million years ago, toolmakers may not have remained long enough in one spot to leave clusters of tools that an archaeologist would notice today.

The earliest simple form of stone toolmaking involved breaking and shaping an angular rock by hitting it with a palm-sized round rock known as a hammerstone. Scientists refer to tools made in this way as Oldowan, after Olduvai Gorge in Tanzania, a site from which many such tools have come. The Oldowan tradition lasted for about 1 million years. Oldowan tools include large stones with a chopping edge, and small, sharp flakes that could be used to scrape and slice. Sometimes Oldowan toolmakers used anvil stones (flat rocks found or placed on the ground) on which hard fruits or nuts could be broken open. Chimpanzees are known to do this today.

Scientists once thought that Oldowan toolmakers intentionally produced several different types of tools. It now appears that differences in the shapes of larger tools were a byproduct of detaching flakes from a variety of natural rock shapes. Learning the skill of Oldowan toolmaking certainly required observation, but not necessarily instruction or language. Thus, Oldowan tools were simple, and their makers used them for such purposes as cutting up animal carcasses, breaking bones to obtain marrow, cleaning hides, and sharpening sticks for digging up edible roots and tubers.

Oldowan toolmakers sought out the best stones for making tools and carried them to food-processing sites. At these sites, the toolmakers would butcher carcasses and eat the meat and marrow, thus avoiding any predators that might return to a kill. This behavior of bringing food and tools together contrasts with an eat-as-you-go strategy of feeding commonly seen in other primates.

The Acheulean toolmaking tradition, which began sometime between 1.7 million and 1.5 million years ago, consisted of increasingly symmetrical tools, most of which scientists refer to as handaxes and cleavers. Acheulean toolmakers, such as Homo erectus, also worked with much larger pieces of stone than did Oldowan toolmakers. The symmetry and size of later Acheulean tools shows increased planning and design—and thus probably increased intelligence—on the part of the toolmakers. The Acheulean tradition continued for over 1.35 million years.

The next significant advances in stone toolmaking were made by at least 200,000 years ago. One of these methods of toolmaking, known as the prepared core technique (and Levallois in Europe), involved carefully and exactingly knocking off small flakes around one surface of a stone and then striking it from the side to produce a preformed tool blank, which could then be worked further. Within the past 40,000 years, modern humans developed the most advanced stone toolmaking techniques. The so-called prismatic-blade core toolmaking technique involved removing the top from a stone, leaving a flat platform, and then breaking off multiple blades down the sides of the stone. Each blade had a triangular cross-section, giving it excellent strength. Using these blades as blanks, people made exquisitely shaped spearheads, knives, and numerous other kinds of tools. The most advanced stone tools also exhibit distinct and consistent regional differences in style, indicating a high degree of cultural diversity.

	More from Encarta
	•  Important Notice: MSN Encarta to be discontinued. Learn more. •  Presidential Myths Quiz •  Coffee break: Recharge your brain