Evolution (Encyclopedia of Science)
The term evolution in general refers to the process of change. For example, one can describe the way in which a section of land evolves over time. Geologic evolution comes about as the result of forces such as earthquakes, volcanoes, land movements, rain, snow, wind, and other factors. In biology, the term evolution refers to changes that take place in organisms over long periods of time. For example, one can study the changes that take place in a population of fruit flies over many generations. The characteristics of that population after 100 generations is likely to be quite different from the characteristics of the first generation of flies.
Scientists and laypeople often refer to the theory of evolution. The term "theory" in this phrase does not refer to a scientific guess, as the term is sometimes used. Instead, the term refers in this case to a large collection of well-established laws and facts about the ways organisms change over time. The theory of evolution is not in any sense an idea whose truth needs to be tested. Instead, it is one of the most fundamental and most important general concepts in all of the biological sciences.
The English naturalist Charles Darwin (1809882) is generally regarded as the father of modern evolutionary theory. However, evolutionary thought can be traced to much earlier periods. In...
(The entire section is 2725 words.)
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Evolution (Encyclopedia of Science and Religion)
There is a common belief that evolution and religion, Darwinian evolution and Christianity especially, are world pictures that are forever opposed. This is a belief today endorsed and promulgated both by extreme evangelical Christians (who support some version of Biblical literalism) and ardent ultra-Dawinians (who hold that their theory necessarily falls into an atheistic mode of thinking). Traditionally, however, this opposition has not been universally accepted. Many people find that there is much in common between the two systems and, thus, great opportunities for sympathetic dialogue. Much of the difficulty and debate arises from ignorance about the various positions involved. This is especially true of evolution. In discussing the idea of selection, it is convenient to make a three-fold distinction between the fact of evolution, the path of evolution, and the theory or mechanism of evolution.
The fact of evolution
The fact of evolution is simply the idea that all organisms, living and dead, came into being by a long developmental process, governed by natural laws, from organisms of a different, probably much simpler, kind. The fact of evolution includes the belief that the original organisms themselves developed by natural processes from inorganic materials. If one wanted to extend from the biological to the cosmological, one would see the fact of evolution as including all developmental change from the time of the Big Bang.
Claims for the fact of evolution were first mooted in the seventeenth century with the extension of Newtonian ideas from the mere running of the universe to its supposed development through natural laws. It was later arguedy, among others, Immanuel Kanthat this happened in a regular fashion as suns and planets were formed from gaseous nebulae. Biological evolutionary ideas began to appear towards the end of the eighteenth century. A prominent exponent in England was the physician and naturalist Erasmus Darwin, grandfather of Charles Darwin; in France a little later the chief advocate of the idea was the biologist Jean Baptiste de Lamarck.
The evidence offered for evolution (then more generally called transmutation) tended to be anecdotal. A major reason why few endorsed the idea with enthusiasm was that it was seen to be a reflection of the ideology of progresspward change in the human social world, and upward change in the history of life, from "monad" to "man." Critics, like the father of comparative anatomy, the French biologist Georges Cuvier, found the idea religiously offensive less because it clashed with literal interpretations of the Bible than because of its underlying philosophy of progress. Such a world picture, in which humans can make the difference unaided, was at odds with the Christian notion of providence, where all depends on God's grace. Although by the mid nineteenth century religious worries were still much in evidence, Charles Darwin met this challenge head on in the Origin of Species (1859), the groundbreaking work in which he introduced his theory. Darwin was not the first to argue for the fact of evolution, but by marshaling so much evidence from paleontology, embryology, geographical distributions, and more, he made the fact of evolution empirically plausible and no longer reliant on an underlying social philosophy for acceptance.
The path of evolution
The path of evolution, or phylogeny, is simply the history of the past as given in the fossil record and as can be discerned indirectly from anatomical and embryological causes and, increasingly, molecular evidence. Thanks to various sophisticated methods of dating, researchers can say that the universe itself is (since the Big Bang) about fifteen billion years old, that the Earth is about 4.5 billion years old, and that life first appeared on the planet about 3.75 billion years ago. Complex life began with the Cambrian explosion about six hundred million years ago; the Age of Mammals began about sixty-five million years ago (although the first mammals go back two hundred million years); the first known ancestors of humans are about four million years old (upright but with ape-sized brains); and, depending on how one measures things, the modern human species Homo sapiens is between five hundred thousand and a million years old.
Traditionally, life is pictured as a tree with contemporary organisms at the ends of the upper branches. However, Lamarck and some other early evolutionists thought that life developed upwards in separate but parallel lines, with variations laid over these. Alternatively, some researcher believe that viruses may carry genes from one line to other, very different, lines, so perhaps a better picture is that of a net. Paradoxically, the main outlines of the history of life were worked out in the first part of the nineteenth century, primarily by those who did not subscribe to evolution, and only later was the process of life given an evolutionary interpretation.
The theory or mechanism of evolution
The theory or mechanism of evolution has garnered many hypotheses. Notorious before Darwin was Lamarck's idea of the inheritance of acquired characteristics, which had not originated with him; Erasmus Darwin had accepted it, as did Charles Darwin much later. In the Origin of Species, Darwin described the mechanism that is generally accepted as the chief force for change: natural selection. More organisms are born than can survive and reproduce, leading to a struggle for survival and, more importantly, reproduction. Given naturally occurring variation, and the fact that those that survive will tend on average to be different from those that do not, there will be a differential reproduction, natural selection. In time this leads to full-blown evolution, and evolution of a particular kind, for selection produces organisms with adaptations. The eye and the hand come naturally as a result of Darwin's causal process.
In the years subsequent to the publication of Darwin's Origin, there have been a multitude of putative alternatives to Darwinian selection, including orthogenesis (a life force driving things), mutationism (major one-step changes), genetic drift (randomness), and molecular drive (DNA has its own built-in ways of change); none has established itself as a full and genuine rival to natural selection. This is not to say that all controversy is therefore quelled. Apart from the question of whether selection can be applied profitably to such issues as the origin of life, there are also questions about the form that life's history will take given selection as the main mechanism of change. Will it be smooth and gradual (phyletic gradualism), as supposed by Darwin and his followers, or will it be jerky and abrupt (punctuated equilibria), as supposed by some leading paleontologists, notably Stephen Jay Gould? Controversy about these issues, however, should not be taken as controversy about other matters. The fact of evolution is firmly established, the main outlines of the path of evolution have been worked out and details are being filled in (for example, that birds are descended from dinosaurs), and selection is taken to be the major mechanism of change even though there are debates about its applicability and its precise results and consequences.
Evolution as fact, path, and theory is a thriving part of the biological sciences, and it is also seen to have extensions and implications for thinking about many other parts of human experience. Social scientists are increasingly turning to evolutionary ideas to flesh out their understanding of human nature and society; philosophers have (after many hesitations) begun to see how evolution, selection even, can profitably deepen their understandings of epistemology (theory of knowledge) and ethics (theory of morality); novelists and poets use evolutionary themes to illuminate aspects of human understanding and motivation; linguists turn to Darwinism for help in grasping the developments of languages; and so it is in many other subjects and disciplines. Although there is still much opposition to evolutionary ideas on various religious fronts, there is realization by theologians and historians that the old story of the warfare between science and religion was much overblown, and many see evolution as an aid to faith and understanding rather than a hindrance.
See also DARWIN, CHARLES; EVOLUTIONARY EPISTEMOLOGY; EVOLUTIONARY ETHICS; LAMARCKISM; SELECTION, LEVELS OF; SOCIOBIOLOGY
Bowler, Peter. Evolution: The History of an Idea. Berkeley: University of California Press, 1984.
Depew, Daniel J., and Weber, Bruce H. Dawinism Evolving. Cambridge, Mass.: MIT Press, 1994.
Desmond, Adrian, and Moore, James. Darwin: The Life of a Tormented Evolutionist. New York: Warner, 1992.
Richards, Robert J. The Meaning of Evolution: The Morphological Construction and Ideological Reconstruction of Darwin's Theory. Chicago: University of Chicago Press, 1992.
Ruse, Michael. Monad to Man: The Concept of Progress in Evolutionary Biology. Cambridge, Mass.: Harvard University Press, 1996.
Ruse, Michael. The Darwinian Revolution: Science Red in Tooth and Claw, 2nd edition. Chicago: University of Chicago Press, 1999.
Ruse, Michael. Can a Darwinian be a Christian? The Relationship Between Science and Religion. Cambridge, UK: Cambridge University Press, 2001.
Ruse, Michael. Darwin and Design: Science, Philosophy, and Religion. Cambridge, Mass.: Harvard University Press, 2003.
Evolution (World of Earth Science)
Evolution is the gradual, cumulative change over time of the characteristics of groups of organisms in a heritable manner. Eventually, these minute changes add up to produce an individual that is markedly different from its distant ancestors, but almost indistinguishable from its most immediate ancestors. These changes are brought about by the organism's genetic response to the environment, and, over the entire course of history, evolution has given rise to all different forms of life on Earth.
Evolution does not occur rapidly on the individual unit of life; changes are too small and slow to be effective at the individual level. In fact, evolution is more efficient at the population
level among groups of organisms that are capable of successfully breeding with each other. With organisms that do not breed with other individuals, the rate of evolutionary change is slower than it is among outbreeding organisms.
Evolution leads to increasing complexity and, eventually, to the production of new species, which survive or become extinct depending upon their reaction to the environment and its continuing changes. Evidence for evolution comes from the fossil record, genetics, and comparative studies.
The mechanism behind evolution is natural selection. Small, individual changes that arise by chance can confer an advantage to those possessing them; this group then has better success at breeding, and successful genes are consequently spread further throughout the population. The theory of evolution is now widely accepted, but when it was first put forward in the nineteenth century by English naturalist Charles Darwin there was much opposition, particularly from religious quarters. Opponents to the theory of evolution often argue for special creation, which states that each type of species was created in the form in which it currently exists, and that no two species are related, by descent, to any other. Most scientists now accept the theory of evolution, as the concept of evolution fits available evidence. There exist some gaps in scientific knowledge of evolution, such as the discovery of the common ancestor for both apes and humans, often referred to as the missing link, but, with time, these knowledge gaps have become smaller.
Evolution does not proceed at a constant rate. At times, a gradual change occurs that allows for a good reconstruction of the process from the fossil record. This is known as phyletic gradualism. The other method of evolution, which can leave gaps in the fossil record is the quicker and more explosive form, called punctuated equilibrium.
See also Cosmology; Evolution, evidence of; Evolutionary mechanisms; Fossils and fossilization
Evolution (Encyclopedia of Food & Culture)
EVOLUTION. Jean-Louis Flandrin, in his introduction to Food: A Culinary History, sets out many of the crucial questions basic to our understanding of the evolution of human diet:
When and how did the eating behavior of human beings diverge from that of other animal species? Did humans distinguish themselves by the type of variety of foods they ate? By the fact that they prepared their food before eating it? By the ceremonial forms with which they surrounded the act of eating? Or by the conviviality of dining and its characteristic social forms? (p. 14)
These questions, as they relate to the evolution of human foodways, remain unanswerable. A major reason is the vast gulf that separates the living from earlier ancestors. Today, virtually all humans subsist on the products of agricultural activities, which include the raising of domestic animals for food. However, this way of life developed very late in the course of human evolution, with the domestication of plants appearing in several locations around the world at some point after 12,000 years ago; the domestication of food animals followed somewhat later. The vast earlier time, during which humans evolved from more primitive beings, was marked by other forms of subsistence. This time span, more than six million years in duration, witnessed dramatic changes in human biology, behavior, and adaptation. Although we have a treasure trove of fossil bones and archaeological materials that document much of this development, there is little in the record that can inform us of the precise dietary items consumed by these remote ancestors of ours, or enable us to answer the questions posed by Flandrin. There are, however, tantalizing hints of the ways of life followed by these earliest members of the human family, and in this essay, this record will be described, and the available evidence for the evolution of human foodways evaluated.
The data at our disposal for this investigation include the fossil bones and teeth of our ancestors, testaments to their evolving biological structures. There are also the residues of their activities, in the very earliest deposits often preserved as parts of natural accumulations of organic and inorganic remains, jumbled in with the fossil bones of very early human ancestors. Later in time, we find the archaeological remains of the actual living areas, where our ancestors slept, made tools, prepared and ate their food, and often buried or left their dead. All this varied information provides important insights about our evolutionary past, but it is very incomplete data for reconstructing dietary patterns. For example, very little in the way of actual food remains is found during archaeological excavations, and only relatively durable items like animal bones are preserved. This may provide some indication of the presence of meat in the diet, but it is not clear just how much it represents the total subsistence pattern and how much was composed of other foods, like vegetables and insects, which leave no archaeological traces. Similarly, the bones and teeth of our ancestors may preserve chemical and other traces of the sorts of foods that were emphasized in their diets, but these signs are often complex and must be carefully evaluated.
Given the difficulties in deciphering the actual residues, other, more indirect, sources of information have come to play an important role in reconstructing the foodways of our ancestors. These data come from the study of our closest living primate relatives, the chimpanzees, and observations recorded from the anthropological studies of those few modern human groups, called gatherers and hunters, who did not practice agriculture, but subsisted on an assortment of gathered vegetable foods, the collection of small animals, such as insects and small vertebrates, and the occasional successful hunting of larger animals. Comparisons with these living examples are often used to furnish clues to what sorts of foods our ancestors consumed. However, correlations of this sort have numerous limitations, and they must be used with caution. Chimpanzees and humans have had separate evolutionary pathways for at least six million years, and it is possible that during this time, chimpanzees have changed as much as humans in their biology and adaptation, making comparisons of living chimpanzees with our earliest ancestors tenuous at best (we have no fossil record of the specific evolutionary history of chimpanzees). Further, those few living gatherers and hunters who have been studied exist in environments that may be dramatically different from the locales of our ancestors. Finally, and perhaps most importantly, our early ancestors were neither bipedal apes nor humans in fur suits, but a series of biologically and behaviorally unique species whose way of life and biology are now wholly extinct.
Both modern chimpanzees and those gatherers and hunters who have been studied, and do not live in very specialized environments (like the Arctic, for example), have somewhat similar diets. The field research by Jane Goodall and her associates on chimpanzees living in the Gombe National Park in western Tanzania, as well as observations from other chimpanzee living-sites in Africa, indicate that these animals are overwhelmingly vegetarians, with a broadly based diet composed, at the Gombe, of the fruits, leaves, stems, blossoms, and gums of more than eighty different plants. Chimpanzees, however, emphasize a variety of fruits as the major part of their diet. Chimpanzees have also been observed consuming insects, sometimes using twigs, specially broken off and trimmed as tools, to obtain termites. Chimpanzees (often males), behaving together in a cooperative fashion, also deliberately hunt, kill, and eat a variety of small vertebrates, including bush pigs, monkeys, and antelopes. Meat, however, makes up a very small percentage of their total diet.
Human gatherers and hunters in tropical or subtropical areas also subsist on a diet that emphasizes a broad array of vegetable food sources, with smaller amounts of insects and vertebrate animals. The exact percentage of each of these elements differs seasonally or yearly, as well as varying between specific groups.
Like living gatherers and hunters, until the advent of agriculture, our ancestors probably lived an unsettled existence, regularly shifting their encampments to new locales in search of resources. Food storage would have been very difficult, and consumption of collected and hunted foods was probably immediate. Groups would have been small, with the social organization flexible enough to allow group size to fluctuate with the seasonal availability of food and other resources.
These comparisons provide only a very limited insight, and for more information, it is necessary to examine the direct evidence from the archaeological and fossil records.
Diet and Human Evolution
A variety of comparative genetic studies document that chimpanzees are our closest living relative. It has been estimated, for example, that humans and chimpanzees share about 98.5 percent of their genetic material. Calculations of the rate of genetic change over time indicate that humans last shared a common ancestor with this African ape between five and eight million years ago. This is the period when the evolutionary line that eventually led to living humans split from the line that led to chimpanzees, representing the beginnings of human evolution. The living and extinct members of this human evolutionary lineage are traditionally grouped into a biological family, the Hominidae, members of which are known as hominids.
We have no fossil or other evidence of the earliest members of the hominid family, just after they split off from the lineage leading to chimpanzees. We do not know what sorts of environments they lived in or what sorts of foods they ate. Because chimpanzees are native to Africa, and the earliest known hominid fossils are limited to Africa, it seems reasonable to place the homeland of the human family on that continent.
The Earliest Hominids
The recognition of Africa as the human homeland first came in 1924, with the discovery of the fossilized skull and jaw of a young child at T'aung, in the Cape Province of South Africa. Named Australopithecus africanus by its discoverer, Raymond Dart, hundreds of additional fossil specimens of this group, known collectively as the australopithecines, have subsequently been uncovered in south, east, and central Africa. There are now at least eight species of australopithecines, sometimes placed in other genera, like Paranthropus or Kenyanthropus. The australopithecines lived in Africa from about four million to perhaps as late as one million years ago. Like all members of the hominid family, they walked upright, allowing them to efficiently carry objects and food. Chimpanzees habitually walk on all four legs. However, the australopithecines were apelike in many of their biological features, possessing small, chimpanzee-sized brains in an apelike skull with a large, projecting face positioned out in front of the braincase. Their teeth were human-like in form, but they possessed massive back chewing teeth, the premolars and molars, that were much larger than those of living humans. The australopithecines, like all hominids, possessed nonprojecting canine teeth. This is in marked contrast to the large, tusklike canines of the apes. Like gorillas, australopithecines also seem to have been sexually dimorphic in body size, with the males considerably larger than the females.
There are fossil bones found in East Africa of still earlier-in-time creatures, for example, Orrorin tugenensis, at six million years, possibly the earliest hominid yet discovered, and Ardipithecus ramidus, who lived about four and a half million years ago, but little is currently known about these creatures and their biology.
The fossil bones of the australopithecines are most often discovered in natural accumulations that are the result of various sorts of geological activities. These fossil bones may have been transported by water over long distances before they were deposited in their final location. They are only infrequently discovered in a context that represents the locale where they actually lived. Thus, little is known about the kinds of environments in which the australopithecines lived, or how the various australopithecine species may have differed in habitat usage or in food choice and general diet.
For many years after the initial discoveries of the australopithecines, there was a prevalent idea that these creatures lived on the open grasslands or savannas of eastern Africa. According to this theory, their habitat would have provided only a limited selection of foods, and was the selective factor responsible for the development of hunting and meat eating. More recent reconstructions, however, have revealed a much more complex environmental context for these early hominids, with evidence for the use of forests and woodlands. Just how important hunting and meat eating has been in human evolution continues to be debated, and its importance in the ultimate appearance of modern humans remains unclear.
Australopithecine fossil bones have been carefully examined in a number of ingenious ways, in order to learn more about their dietary patterns, but thus far with only limited success.
For example, on the basis of comparisons with the teeth of other mammals, it is clear that these early hominids were not specifically adapted to meat eating. As in modern humans, the chewing surfaces of the teeth are covered with thick layers of enamel. Some australopithecine species, known as the ''robust" australopithecines, possessed truly massive back teeth, along with very large jawbones to house them, and large chewing muscles, sometimes so large that they formed a crest on the top of the skull. These general biological features of australopithecine jaws and teeth suggest that they emphasized the chewing of coarse vegetable food sources, but not the consumption of grasses, whose high cellulose content would have been very difficult for these creatures to digest.
Other studies of the dentition have attempted to determine more specific aspects of the dietary patterns of the australopithecines. One series of studies utilized scanning electron microscopy to examine the minute scratches and pits left by food particles on the chewing surface of the teeth. The results of these observations suggest that some of the australopithecines ate a diet rich in fruits, while others were consuming a more varied, but basically vegetarian, diet. One problem with these sorts of studies is that they tend to focus on the final meals the creatures ate before they died, providing a somewhat limited view of their overall diet, especially if they were seasonally exploiting a variety of different habitats and foods.
Other studies have examined the chemical composition of australopithecine fossil bones. One study employed the ratio of calcium and strontium in the fossil bones to determine whether the australopithecines were generally herbivorous, carnivorous, or omnivorous.
Another chemical analysis, based on staple isotopes including 13C and 12C, has reached a conclusion similar to that from the calcium-strontium analyses: some australopithecines, at least, were consuming animal foods, though the identity of these animals, and whether they were vertebrates or invertebrates, has not been determined.
These studies continue to support a variety of opinions about the dietary patterns of these early hominids, with some anthropologists suggesting a diet based primarily on fleshy fruits, nuts, and seeds, while others advocate a more broadly based diet, including some animal foods.
There is no direct evidence that the australopithecines collected foods to be brought back to some central camp to be consumed as part of a group activity. Rather, like chimpanzees, it appears likely that they consumed food continuously as they foraged in their environment.
The Evolution of the Genus Homo
Good evidence of the evolution of members of our genus, Homo, begins to appear around two million years ago at sites in East Africa. There was a dramatic increase in brain size, from the 500 ml common in the australopithecines to brains as large as 800 ml in these early humans (though still about half the size of those of living people). They also possessed smaller back chewing teeth. Chipped stone tools, first used about two-and-a-half million years ago, now became more common. These durable tools, made from water-rounded pebbles, are known as Oldowan tools. They were made by striking two stones together, knocking off chips to produce a cutting edge or point. Though crudely made, their development represented a major advance in the ability of the early hominids to exploit a wider variety of food sources. Hominids lacked sharp and hardened claws, as well as projecting and pointed canine piercing teeth, making them inefficient in dealing with many potential food sources. For example, without a digging tool or claws, many subterranean foods like insects, small burrowing mammals, tubers, and rhizomes, would have been impossible to obtain. The australopithecines are only rarely found in association with these chipped pebble tools, and most anthropologists believe the first stone tool makers were early members of the human genus Homo.
Also found at this time are animal bones, mainly from antelopes, with butchery marks made by a sharp stone edge. Although isotopic studies have indicated that the earlier australopithecines may have consumed animal foods, these cut marks represent definitive evidence of early meat eating. What is still being debated is the origin of these bones. They may have been the result of hunting activities, which is entirely reasonable given our knowledge of the cooperative hunting patterns of chimpanzees, but some scientists have suggested that they may also have been the result of scavenging activities. A safe way, it is said, to obtain bones with scraps of meat still adhering to them would be to claim animal bones from a predator kill after primary scavengers, such as hyenas and jackals, have finished with them. Thus, the initial meat eating in human evolution, according to this view, was to utilize stone tools to scrape off bits of rotting tissue from the bones of predator kills. One major flaw with this notion is that no primate is equipped with digestive mechanisms to protect them from the serious consequences of eating spoiled meat.
By about 1.8 million years ago, there are a number of different species of early Homo coexisting in eastern Africa. In addition, several species of robust australopithecines were also living at this time. What the possible dietary differences, if any, between all these hominids is unknown.
Expansion Out of Africa
At some point after 1.8 million years ago, in one of the most momentous events in human evolution, the hominids begin to move out of Africa. One site along the Jordan River Valley in Israel, dated at about one and a half million years old, is located along what must have been a major route into Eurasia. Along with stone tools similar to those from Africa were found numerous bones of African mammals, suggesting that the hominids were not the only creatures moving out of that continent.
Hominid sites in the Republic of Georgia and on the island of Java also testify to this dramatic increase in range. Although the reasons the hominids left Africa at this moment are unclear, one reasonable explanation is that stone tools enabled hominids to expand the range of dietary items open for exploitation, allowing them to move into new habitats.
During the course of the next million years, hominid brain size increased, so that by about 300,000 to 400,000 years ago, the volume of the braincase reached 1,200 ml, within the range of living humans. It may be that there was an associated increase in body size during this period as well. Increasing brain size would have required greater intakes of oxygen, as well as nutrients. It has been suggested that this brain size expansion relied on increased amounts of dietary fats. Hunted animals could have supplied these fats, but gathered insects, many of which are richly endowed with this nutrient (especially the essential fatty acid, linoleic acid), are equally likely sources. Larger body size also necessitated a greater number of calories.
The occupation of the European subcontinent appears to have taken place later than human expansion into more hospitable habitats in Asia. This is no doubt related to the presence of glaciers, which, beginning about two million years ago, periodically covered major parts of Europe. The earliest occupation site in Europe, dating to about 800,000 years ago, is located in northern Spain, near the present city of Burgos. From that time onwards, hominid presence in Europe was closely tied to the advance and retreat of the glaciers, with the continent relatively uninhabited during times of maximal glacial activity.
By 500,000 years ago, hominids, placed in the category Homo erectus, were intermittently occupying a large cave on the outskirts of what is now the village of Zhoukoudian, about twenty-five miles from Beijing, in northern China. Although there was no glacial activity in this part of Asia, winter would have been severe (Zhoukoudian is about as far north as Philadelphia). While it remains unclear if hominids actually wintered this far north, the earliest well-documented evidence of fire has been found here. Fire allowed hominids to use food sources that would be uneatable, or actually toxic, without cooking. Burned deer bones, as well as those with cut marks, testify to the use of meat by the inhabitants of the cave, but whether the meat was obtained by hunting or scavenging remains unknown.
From about the same time, a hominid skull was found in Ethiopia with cut marks on its frontal bone, suggesting skinning or scalping. Cannibalism has been documented at a number of other, later-in-time hominid sites; was the flesh a part of the diet, or was eating a dead friend or relative part of a ritual?
Modern Human Origins
The last 200,000 years of human evolution are much richer in data because actual living places have been located and excavated. Prior to this time, only a very few sites, like Zhoukoudian, represented the remains of an encampment, where the evidence of hominid activities are directly preserved. By about 115,000 years ago, our ancestors had begun the practice of the deliberate burial of their dead, thereby reducing the risk that the body would be destroyed by scavengers. Burying the dead resulted in a vast increase of ancient skeletons that have been preserved for study.
There continues to be debate about the precise way by which living humans emerged from our earlier ancestry. Some anthropologists suggest that modern humans evolved from these earlier hominids and, thus, are the culmination of a very long evolutionary history in various geographic areas. For example, living Asians are the descendants of ancestors who reached Asia more than a million years ago.
Most anthropologists support another theory, that all modern humans originated in Africa some 100,000 to 300,000 years ago and, subsequently, spread out from there to populate the rest of the planet, replacing the earlier hominids who were already living in these areas, descendants of the much earlier initial expansion.
One extinct fossil group that has figured prominently in these theories is the Neanderthals, a group of hominids who lived in Europe and the Middle East from about 130,000 to about 30,000 years ago, when they disappeared from the scene. Because they lived in Europe, where the most intensive archaeological investigations have taken place over the last 150 years, we have much more evidence about these creatures than about any other fossil hominids. This has provided a rich data source, but it also has a number of serious limitations. The most important is that emphasizing the Neanderthals gives a very Eurocentric view of human origins. The final glaciation occurred during much of the time Neanderthals were in Europe; this made major portions of the continent uninhabitable. Those parts that could be occupied by humans represented marginal environments that would have limited population density to extremely low levels.
Given the harsh environments of Europe in which the Neanderthals were living, vegetable foods were probably relatively scarce through much of the year, and meat was almost certainly a major dietary resource. This is confirmed by chemical analyses of their bones, which indicate that for some Neanderthals, fully 80 percent of their diet came from meat. The bones of numerous large animals, such as deer, aurochs, wild boar, and horses are preserved at Neanderthal sites, along with smaller animals. At sites along the Mediterranean, shells testify to the consumption of seafoods. Our evidence for the diet of peoples contemporary with the Neanderthals, but living in Africa and southern Asia, remains limited. At one site, located on the very southern coast of Africa, Klasies River Mouth Cave, there is abundant evidence of the use of a variety of food resources, including land and sea animals and shellfish. Because much of our current evidence comes from humans, like the Neanderthals, who lived in a harsh environment, the emphasis on hunting and meat eating that has come to characterize the diets of earlier hominids may represent a very biased picture.
Although the precise evolutionary relationships of the Neanderthals to living humans remain shadowy, excavation of their sites has revealed a complex picture. Often, living areas with hearths and signs of social areas around them have been uncovered. The bones of selected parts of animals, often with butchery marks on them, are scattered about. Clearly, Neanderthals, like living human gatherers and hunters, were carrying back to a central camp chosen pieces of animals. They may also have brought back other dietary items from their foraging and hunting activities, but the relative absence of small animal bones suggests that they may have been consumed immediately where they were found. It is quite possible that they sat around a fire sharing and consuming food, perhaps engaging in the uniquely human dinnertime interactions of storytelling and discussions of the day's activities. It is unclear, however, if the Neanderthals were actually able to use language, so this reconstruction remains a tentative one.
Sometime after 40,000 years ago, modern human-like peoples appeared in Europe, perhaps migrating there from their origins in Africa, or developing from ancestors already living in Europe. These modern humans brought with them new sorts of tool-making technologies, based on a broader array of raw materials, such as ivory, bone, and wood, with a wider assortment of beautifully made stone tools that show far greater sophistication than those made by the Neanderthals. The first artistic expressions also made their appearance at this time, with plastic art in the form of ivory and bone carvings of animals and people. Deep inside caves, they produced engravings and painted images of animals, and occasionally humans, some of them of great genius.
The sites occupied by these modern humans are littered with the bones of the same sort of animals, the earlier Neanderthals hunted, but the concentrations of bones indicate greater skills in hunting and a corresponding larger number of captured animals. This is also the case with much larger accumulations of shellfish along the coast.
These early modern humans continued this sort of hunting activity to the end of the last glacial period, about 12,000 years ago. In Europe, the retreat of the glaciers resulted in the spread of forests and a major change in dietary habits, with peoples hunting forest animals, like deer and rabbit, and utilizing to a much greater extent the riches of the sea. By this time, however, peoples in the Middle East and along the Yangtze River Valley in southern China were beginning to experiment with the cultivation of plants, which represented the beginnings of the agricultural revolution, and formed the foundations of settled urban life and the origins of civilization.
Although this sketch brings together much of our current knowledge of the evolution of human foodways, much clearly remains to be learned. For one thing, it tells us little about how human diet changed from eating what was necessary for nutritional needs to consuming what was enjoyable and pleasant to eat. Perhaps our ancestors always selected those foods that were enjoyable to eat, bringing about the basis of the consumption of food as a central focus in the social life of humans.
See also Agriculture, History of; Cannibalism; Hunting and Gathering.
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