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Biology: Zoology

Biology: Zoology


Zoology is the study of animal life from molecules to whole animal societies and ecologies, from physiological and reproductive processes that take less than a second to evolutionary histories that extend over many millions of years. Zoology is one of the oldest scientific disciplines and one close to human interest, since animals play an important role as pets, beasts of burden, and livestock.

Historical Background and Scientific Foundations

The study and classification of animals as a scientific discipline began with the ancient Greek philosopher Aristotle (384–322 BC) in the fourth century BC. Aristotle's works combined the conventional wisdom of Greek society with his own investigations (which included dissections) and those of others. The number of animals that Aristotle could observe was limited, however, and he depended on “traveler's tales” for much of his information. Although such reports were usually more fable than fact, Aristotle evaluated them critically. For example, he denied the popular belief that elephants, whose existence was near-legendary in Greece, had no knee joints and had to lean against trees to rest.

Aristotle was interested in animals and their behavior. His major surviving zoological works, History of Animals, Parts of Animals, and Generation of Animals, reflect his belief in accurate data collection as the foundation of any scientific exploration. He also began one of the major traditions in zoology—the effort to define species and determine the criteria on which the animal kingdom was to be defined.

Unfortunately, Aristotle's lead was not followed for many centuries. While zoology's sister science, botany, always attracted interest because of plants' many medical uses, few animal studies had such practical application. Zoology after Aristotle was largely the work of natural historians such as the first-century AD Roman scholar Pliny the Elder (AD 23–79), whose voluminous Natural History was drawn partly from his observations, but also from many other sources. It recounts many legends and myths in addition to concrete information.

The Middle Ages

In the Middle Ages, zoological writing was dominated by the bestiary, a collection of ancient animal stories given moral and allegorical interpretations. Many of these stories, and some of the animals, were mythical. For example, it was widely and incorrectly believed that when pursued by a hunter, a male beaver would bite off its own testicles, thought to have medicinal value, in hopes that the hunter would take them and be satisfied. If pursued again at another time, the beaver would show the hunter that it lacked the desired appendages, and the hunter would leave him unharmed.

Bestiaries were not the only medieval zoological writings. There were also more practical works aimed at hunters and agriculturalists. Holy Roman Emperor Frederick II (1194–1250), a keen falconer, wrote a treatise on birds of prey that contains an extended discussion on migration as well as other ornithological information, although the text had little influence on subsequent zoologists.

The revival of Greek and Arabic scientific learning, which affected many disciplines in the high Middle Ages, also had little effect on zoology. Although Aristotle's works were known, they did not receive much attention. Unlike botany, which continued to be associated with medicine, zoology was not studied in medieval universities.

The Renaissance

Knowledge of animals expanded rapidly in the Renaissance. Humanists rediscovered the works of ancient writers like Aristotle and Pliny, and the age of exploration vastly increased the number of animals known to European investigators.

Many sixteenth- and early-seventeenth-century zoologists were “encyclopedists,” working primarily (but not exclusively) from their desks, compiling textual information rather than observing and/or dissecting animals. Zoologists like Swiss physician Konrad Gessner (1516–1565) drew from ancient and medieval sources, contemporary travelers, and other writers on animals along with their own firsthand observations to produce books about animals, whose role in history, proverbs, mythology, and other areas of human culture was as important as we would now deem biological information.

Renaissance zoologists devoted far more space to animals with a prominent cultural role, such as horses, eagles, and bees, than to the obscure animals, such as those of the New World, which had few associations for Europeans. Whether or not the animals actually existed was also still a question of secondary importance. Gessner even included such legendary creatures as the unicorn, phoenix, and sea serpent in his four-volume History of Animals (1551–1558).

The great chain of being—the belief that all forms were linked in a hierarchy descending from God—was still largely accepted at this time. Other Classification schemes were based mostly on obvious physical resemblances, or on Aristotle. Gessner, for example, included bats among birds as intermediary forms between birds and mice. But this had problems too. Whales and porpoises, which we now know are mammals (a term not invented until the eighteenth century), were not included in that group. Most mammals at that time were called quadrupeds, or four-legged animals; animals that lacked legs entirely could not be included. Even once the major groups of animals had been defined, it was often difficult to arrange individual species within the group. Rather than finding a system for classifying every kind of animal based on natural characteristics, Gessner listed animals alphabetically within broad categories. This meant that his arrangement changed every time the book was translated.

One of the great challenges for European zoologists in the sixteenth and seventeenth centuries was a flood of information about animals unknown to the ancients that came from the Americas. New World natural histories were published that described and discussed animals, although zoology often took second place to botany. In addition, New World natural historians differed from encyclopedists. Lacking centuries of European literature and cultural associations, descriptions of American animals were more limited to direct observations and dissections. Bizarre animals like opossums and rattlesnakes attracted legends, but American zoology was generally more pragmatic than the discussions of European animals, focusing on structures, behaviors, and economic uses.

The encyclopedists' ideal of gathering everything said about an animal, true or not, also came under fire

in the seventeenth century from the opponents of “vulgar errors,” who subjected encyclopedist claims to empirical validation. English physician Sir Thomas Browne (1605–1682) attacked many popular superstitions in his Pseudodoxia Epidemica, or, Enquiries into Very many received Tenets, and commonly presumed Truths (1646), also called Browne's Vulgar Errors. Browne used experiments to attack traditional beliefs such as that spiders and toads were “natural enemies” who would always fight each other. Browne put a toad and some spiders in a jar and noted that the spiders crawled around undisturbed by the toad's presence, while the toad ate them, one by one. By the late seventeenth century zoology books focused more narrowly on the description, characteristics, and anatomies of specific animals rather than their symbolic roles in the larger cultural system.

The Age of Classification

The English naturalist John Ray (1627–1705), the greatest zoologist of the late seventeenth century, tackled the problem that would obsess zoologists for the next century: how to classify animals. Ray's system was based on internal physical characteristics like anatomy more than external similarities, although he still divided birds into land and waterfowl and with some misgivings included whales and dolphins as a special group among the fishes, suggesting the term “quadruped” be abandoned.


Opossums were the first marsupials known to Western science. Since the other members of the group, such as the kangaroo, are restricted to Australia, when the opossum was first encountered in America it seemed unique and bizarre. The mystery and legend that surrounded the animal can be seen in William Byrd's Natural History of Virginia. William Byrd (1674–1744), a Virginia landowner, published the book to attract immigrants, and his descriptions of most Virginia animals emphasized their practical uses. The description of the opossum, by contrast, is soaked in legend rather than observation, and describes an utterly weird creature:

This animal is found nowhere else in the whole world except in America; it is a phenomenon among all animals living on land. Its shape and color are similar to a badger. The male's genital member sticks out in the back, because of which they turn backs to each other at the time of copulation. The female bears her young in the teats, or breasts, at which they grow. At first they are no larger than a pea, and cling fast to them before they seem even to be alive. This animal has another stomach; in addition to the natural one, in which it carries its young—after they fall away from the breasts—until they can help themselves. Meanwhile they run in and out of it as they desire, until they have become large. If a cat has nine lives, as one commonly says, then this animal has certainly nineteen, for if all the bones in its body are broken, so that it lies there as if dead, still it recovers again in a short time, and very soon gets well again.

SOURCE: Byrd, William. William Byrd's Natural History of Virginia. Richmond, VA: Dietz Press, 1940.

Comparative anatomy also advanced in the late seventeenth century, thanks to studies by English physician Edward Tyson (1650–1708) and anatomists associated with the French Académie des sciences (Academy of sciences). Tyson's work includes some of the first monographs devoted to the dissection of particular animals, including a dolphin, which he demonstrated was not a fish, and an “orang-outang” (actually a chimpanzee) whose human appearance Tyson emphasized, arguing that the ape was more like a man than a monkey—another intermediate on the great chain of being. Entomology was also booming. Insects could be observed and collected more easily than large animals. Their life cycle also received close attention, and the recently invented microscope was used to study them and other small creatures.

The greatest classifier of the eighteenth century, the Swedish naturalist Carl Linnaeus (1707–1778; also known as Carolus Linnaeus or Carl Linné), is best known for his botanical studies, but he extended his classification scheme to the animal realm as well. His nested hierarchy of animal classifications drew on a number of different traits rather than being arranged around a single characteristic. Linnaeus established many of the basic categories used today—for example, he permanently removed cetaceans from the class of fish, insisting that the production of breast milk by females was the defining characteristic of the class of mammals, a word derived from the Latin for “breast.” (His identification of rhinoceri as rodents, however, was less successful.) In both botany and zoology Linnaeus systematized the use of binomial nomenclature—the identification of each species by two Latin words, one for the genus and the other for the species itself. The tenth edition of his Systema Naturae (System of nature), published in 1735, is considered the starting point for modern zoological naming.

At the top of Linnaeus's system were six classes of animals. Four were vertebrates—mammals, birds, amphibia (a class that includes modern reptiles), and fish. Two were invertebrates—insects, including modern arthropods, and a huge catchall class called vermes, or worms.

Linnaeus's great rival was a French nobleman, Georges-Louis Leclerc, Comte de Buffon, the supervisor of the Jardin du Roi, the royal botanical garden (which also conducted zoological research). He was the author, along with numerous assistants, of the multivolume Histoire naturelle, générale et particulière (Natural history). Unlike Linnaeus, however, Buffon specialized in vertebrates. He was interested in particularity—traits that distinguish individual kinds of animal—rather than generality, those that are shared with other animals. He was also more interested in animal behavior than anatomy and conformation.

In addition, while Linnaeus was primarily a classifier, Buffon believed classification schemes imposed an arbitrary set of human assumptions on the chaos of nature. Rather than invent new classification schemes, he argued, natural historians needed to observe individual animal species, which he defined not by conformity to an archetype, but as a collection of individuals who could mate and reproduce.

Buffon's emphasis on behavior was rejected by most of his French successors, who focused on anatomy and classification, working more from dissections than live observation. The tradition of observing animal behavior was stronger in England, where a school of naturalists,

many of them clergy, focused on close observation of local fauna. The reverend Gilbert White's (1720–1793) Natural History and Antiquities of Selborne, first published in 1788 and reprinted innumerable times thereafter, contains many reports of White's close firsthand observations of animals. Although its influence on zoology as a science was slight, it increased popular interest in the subject in the nineteenth century.

Although Buffon, Linnaeus, and others purged eighteenth-century zoology of the menagerie of fantastic creatures it had inherited from antiquity, the Middle Ages, and the Renaissance, the number of animals zoologists could investigate had still vastly increased. Like botany, zoology was transformed by the information brought back from explorations, including exotic tales, drawings, skins, teeth, skeletons, preserved specimens, and living creatures. Some of these creatures, most notably the platypus (Ornithorhynchus anatinus), which had the fur and mammary glands of a mammal but laid eggs like a bird or reptile, posed thorny problems of classification. In addition, the opossum no longer stood as the lone marsupial, since the exploration of Australia, beginning in the late eighteenth century, introduced scores of others, including the kangaroo and the koala.

Other increasingly important sources of zoological information were several impressive discoveries of fossilized animals. Growing knowledge of anatomy enabled scientists to relate fossil animals to living species. Many fossils, however, seemed to be of animals no longer in existence. The strangeness of some of them raised the important question of extinction—could a species actually die out to the last member?

It was difficult to answer this question with a firm “yes” when much of the earth's surface remained unknown to European science and supposedly extinct species could still be living in some remote place. American President Thomas Jefferson (1743–1826) hoped that Lewis and Clark's expedition would find surviving mammoths in the interior of America. While it failed to do so, it did add several previously unknown species to Western zoological knowledge. The finding of animals thought extinct in remote, previously inaccessible areas of the globe remained a staple of the “lost world” genre of popular fiction well into the twentieth century.

Extinction also involved religious issues, such as whether God would allow a species He had created to disappear. If a creature could disappear, did that imply creation was imperfect? In addition, zoological evidence was often adduced to show the perfection of God's design, as in the creation of complex organs such as the eye or in the harmony with which different organs worked together to sustain life.

The Museum of Natural History and Comparative Anatomy

Zoology in the late eighteenth and early nineteenth centuries was dominated by dissection and comparative anatomy rather than the study of living animals. France was the intellectual center of zoology, and its leading institution was the Museum of Natural History, founded during the French Revolution in what had been Buffon's royal botanical garden. Two professors at the museum, Jean-Baptiste Lamarck (1744–1829) and Georges Cuvier (1769–1832) established many of the fundamental taxonomic groups used by modern zoologists.

Lamarck broke up Linnaeus's enormous and imprecise categories of worms and insects into a larger number of much more precisely defined groups. Cuvier integrated fossil animals with the living world and came down firmly on the side of extinction, although he did not believe new species had appeared since Earth's creation. Both Lamarck and Cuvier rejected the idea of a great chain of being in which all species were arranged in a single hierarchy. Cuvier's skill at dissection and comparative anatomy also marked an important stage in the development of zoology as an independent science. Before Cuvier, important comparative anatomists like Tyson had been physicians who had learned how to dissect in medical school. Cuvier had no medical training—his

anatomical skills had been acquired for the study of animals, not people.

Along with another professor at the museum, Étienne Geoffroy (1772–1844), Cuvier and Lamarck fought out the principal theoretical conflicts in early nineteenth-century zoology. Cuvier championed the fixity of species against Lamarck's belief in evolutionary transformation. Cuvier approached animal anatomy as a functionalist, emphasizing the perfection with which each animal was adapted to its environment and the harmony with which its organs worked. He argued that any fundamental change in an animal's body would render it unable to survive. The heir of Buffon's suspicion of fixed species, Lamarck believed that all living creatures underwent constant, gradual changes that produced new species from old ones. Partly through argument and partly through political skill, Cuvier defeated Lamarck, who became increasingly marginalized and bitter.

Cuvier's quarrel with Geoffroy, though, was not about evolution but about the relationships between different kinds of animals. Cuvier divided the animal kingdom into four entirely distinct classes, each defined by their nervous systems: vertebrates, molluscs, articulata (jointed invertebrates, including insects), and radiata (a somewhat catchall group defined by their rudimentary nervous systems and radial organization). Geoffroy insisted on the unity of the animal kingdom, insisting that all animals were variations, not on Cuvier's four basic forms, but on one. In 1830 a final confrontation between Geoffroy and Cuvier at the Academy of Sciences, France's leading scientific society, ended in a victory for Cuvier—and a defeat for French science, as the strength of the Cuvier tradition, with its insistence that species could not change, greatly hindered the spread of evolutionism in nineteenth-century France.


Although Charles Darwin's (1809–1882) zoology is often associated with the exotic animals he studied as naturalist on the HMS Beagle, he was also a keen observer of domestic animals. In his 1872 book Expression of the Emotions in Man and Animals Darwin analyzed his observations of horses, dogs, and other animals commonly found in Victorian England in an evolutionary context:

Dogs and jackals take much pleasure in rolling and rubbing their necks and backs on carrion. The odour seems delightful to them, though dogs (at least well-fed dogs) do not eat carrion. Mr. Bartlett has observed wolves for me, and has given them carrion, but has never seen them roll on it. I have heard it remarked, and I believe it to be true, that the larger dogs, which are probably descended from wolves, do not so often roll in carrion as the smaller dogs, which are probably descended from jackals. When a piece of brown biscuit is offered to a terrier of mine and she is not hungry (and I have heard of similar instances), she first tosses it about and worries it, as if it were a rat or other prey; she then repeatedly rolls on it precisely as if it were a piece of carrion, and then eats it. It would appear that an imaginary relish has to be given to the distasteful morsel; and to effect this the dog acts in his habitual manner, as if the biscuit were a live animal or smelt like carrion, though he knows better than we do that this is not the case. I have seen the same terrier act in the same manner after killing a little bird or mouse.

SOURCE: Darwin, Charles. The Expression of the Emotions in Man and Animals. New York: D. Appleton and Company, 1899.

The Discipline of Zoology in the Nineteenth Century

One of the most important developments in nineteenth-century zoology was its entrance into the structure of academic disciplines. Few great zoologists before the 1800s had been university scholars. During the nineteenth century universities created zoology and comparative anatomy departments, which led to academic conferences and specialized scientific societies. The first scholarly journal devoted exclusively to zoology, the British Zoological Journal, appeared in 1824; the French Magasin de Zoologie followed in 1831.

Not all zoology took place in university settings, however. The zoo emerged as a research center, not just a place to gawk at strange and exotic animals. This apparatus created academics who did unglamorous work on a variety of often unglamorous organisms, adding to a constantly growing body of knowledge. The amateur tradition of natural history remained strong as well, particularly in Britain, which had a comparatively weak university sector. Explorers continued to discover new species in remote areas. The existence of the okapi (Okapia Johnstoni) for example, only became known to Western science in 1901, when Sir Harry Johnston (1858–1927) brought back a skin, although Africans had long known of it.

The nineteenth century also saw the spread of a standardized Latin system of zoological names, based on Linnaeus's binomial nomenclature. This enabled zoologists to communicate with each other across language barriers much more effectively and helped the discipline become truly international. The rules of animal naming are found in the International Code of Zoological Nomenclature, maintained by the International Commission of Zoological Nomenclature, founded in 1895 in London.

Evolution and Zoology

The work of British naturalist Charles Darwin (1809–1882) bridged several disciplines, but his main area of study, which laid the foundation for evolution, was zoology. Much of his work on the voyage of the HMS Beagle consisted of examining the different animals that the ship encountered on its voyage. Studies of the expedition's zoology were published in several volumes, and Darwin would go on to write, in addition to his well-known evolutionary works, zoological classics on barnacles, earthworms, and the expression of emotions. Darwin drew from the English natural history tradition of close observation of living animals as well as the continental tradition of comparative anatomy.

“Darwin's finches,” for example, were a group of birds indigenous to the isolated Galapagos Islands in the Pacific. Darwin observed that there were several different species of finches (modern zoologists identify 13), principally differentiated by the shapes of their beaks—which for birds is strongly associated with diet. The ability of one type of finch to occupy several ecological niches helped Darwin realize the importance of natural selection and change over time. He suggested that an original finch species, arriving on an island without an established bird population, developed into separate species to take advantage of different opportunities—a

phenomenon that later zoologists called “adaptive radiation.” Remote islands, with their evolutionary isolation, produce some of the world's most unusual species and were the object of intense zoological study in the nineteenth and twentieth centuries.

Over time, evolution permeated every aspect of zoology. The theory gave zoologists a central organizing concept, in which differences between related species appeared over time by descent with modification and were evaluated in terms of natural selection. Classification schemes were not simply groupings of like with like, but attempts to reconstruct webs of evolutionary relationships.

The other important nineteenth-century scientific influence on zoology was the discovery of genetics. Although Gregor Mendel's famous experiments involved plants, not animals, his principles were quickly applied to the animal world as well. This also disproved the belief that animals could pass on acquired (not inherited) traits to their offspring, an idea often called “Lamarckian” even though Darwin shared it.

Twentieth-Century Zoology

Like other biological disciplines, twentieth-century zoology became a laboratory science. Technological advances, such as the development of the electron microscope, allowed scientists to study biological processes directly. In many universities laboratory work in molecular and cell zoology surpassed the study of whole organisms or communities of organisms. Independent zoology departments were folded into molecular biology programs, and many whole organism studies, such as entomology and herpetology, declined in favor of molecular and genetic studies. This led some organismal scientists to decry the “reductionism” of modern zoology—the assumption that studying the whole animal is unnecessary given the ability to study its parts.

Despite these protests, laboratory study of protein chemistry and genetics solved many long-standing puzzles of zoological classification, such as whether flamingos should be classed with geese or storks. They exhibit behavioral and anatomical characteristics of both groups, but examination of their genetic sequences has placed them with the storks. Because different evolutionary pathways can lead to similar results, a phenomenon know as convergent evolution, genetic links between species and groups are more certain than those established by observation.

In direct contrast to the laboratory zoologist who may seldom encounter a living organism is the field observer of animals in their natural habitats. The pioneers of this discipline were Dutch ornithologist Nikolaas Tinbergen (1907–1988) and German zoologist Konrad Lorenz (1903–1989). Their efforts were crowned with the 1973 Nobel Prize for physiology or medicine in 1973, an award shared with German animal behaviorist Karl von Frisch (1886–1982) in recognition of his work elucidating how honeybees communicate. Tinbergen and Lorenz studied animal behavior in a natural environment instead of in controlled laboratory conditions. Their early twentieth-century animal behavior studies, or ethology, established the concept of instinct.


Nikolaas Tinbergen (1907–1988), one of the founders of ethology, the science of animal behavior, was born to an academic family in the Netherlands. Interested in nature from his youth, Tinbergen was active in the Nederlandse Jeugd-bond voor Natuurstudie (Dutch youth organization for nature studies) and educated in biology at the University of Leiden. Although his major interest throughout his life was birds, he wrote his Ph.D. dissertation on the bee-hunting wasp found in Holland's sand dunes. Tinbergen used field experiments, altering the surroundings of the wasps' burrows to determine how they returned to them after hunting. His dissertation was one of the shortest on record—only 29 pages!

After receiving his doctorate, Tinbergen was accepted on an official Dutch expedition to Greenland, where he lived with an Inuit family and studied local animals, including snow buntings (Emberiza) and sled dogs. On his return to Holland he taught at Leiden and met the other giant of early ethology, the German zoologist Konrad Lorenz (1903–1989). The two became lifelong friends, with one interruption caused by the Second World War. The German authorities occupying Holland made Tinbergen a prisoner, while Lorenz was an enthusiastic Nazi who served as a medical officer in the German army and spent several years in a Soviet prison camp. It was not until 1949 that the two were reconciled.

Tinbergen left Leiden for Oxford, where he spent the rest of his career, in 1949. The reasons for this are not clear, but he desired a closer intellectual connection with the anglophone world and found the pettiness of post-war Holland stultifying. (Tinbergen always resented his home country for what he saw as its destruction of the beaches—whose animals he had spent so much time studying—for the sake of economic development.)

Tinbergen's development of the concept of ethology, for which he would share the 1973 Nobel Prize for physiology or medicine with Lorenz and Karl von Frisch (1886–1982), was based on observing animals' actions rather than speculating on their subjective feelings. His famous four “whys” of animal behavior are causation, the immediate stimulus and physiological process that produced a behavior; ontogeny, the development of the behavior in the individual; function, the purpose of the behavior; and evolution, how the behavior evolved in the species.

Unlike laboratory-oriented disciplines such as biology, live animal observation studies are more appealing to the public. Lorenz and British primatologist Jane Goodall, for example, published popular books for a general audience; such studies are also particularly suitable for film and video. Movies and television have made observers of well-known species, such as Goodall, who studied chimpanzees, or Dian Fossey, who studied mountain gorillas, some of the world's best-known scientists.

Technology has influenced animal behavior studies in many ways. Cheap, reliable, and frequent transportation has made it easier to study numerous species and habitats. Studies of animal territorialism and migration patterns have been revolutionized by the use of radiotelemetry—radio tags and collars. Behavioral observers are no longer limited by what they can remember or summarize in writing, but use film or video to capture animals in action.

Modern Cultural Connections

Like all of biology, zoology has been affected by the growing field of genetics. The ability to compare DNA across different species has vastly improved our knowledge of evolutionary relationships. Zoology also answers questions about human beings and their behaviors. A pioneer in this field was Desmond Morris (1928–), a student of Tinbergen's who applied ethological techniques to humanity in his 1967 bestseller The Naked Ape. Human implications are often drawn from primatologists' studies, and studies of male and female primates influenced debates over feminism and human gender roles. Zoological research has also contributed to such topics as altruism and the “selfish gene.”

Perhaps the greatest challenge to modern zoology, though, is that so many animal species are being driven into extinction or survive only in zoos, where much of their natural behavior cannot be studied, while vast ranges of animal habitat are being destroyed. In areas of rapid change, like the Amazon, species are becoming extinct before their existence is even known. Zoologists like Fossey, murdered by poachers in 1985, have become leaders in efforts for the preservation of endangered species and the conservation of wilderness habitats, often under the banner of “biodiversity.” American sociobiologist and entomologist Edward O. Wilson (1929–) the world's leading authority on ants, also works and writes for the preservation of natural habitats and creatures, one of many eminent zoologists active in the cause.

See Also Biology: Botany; Biology: Classification Systems; Biology: Comparative Morphology: Studies of Structure and Function; Biology: Concepts of Heredity and Change Prior to the Rise of Evolutionary Theory; Biology: Developmental Biology; Biology: Ecology; Biology: Evolutionary Theory; Biology: Marine Biology; Biology: Miller-Urey Experiment; Biology: Ontogeny and Phylogeny; Biology: Paleontology; Biology: Sociobiology.



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Bill Burns

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