A book is a set of written, printed, illustrated, or blank sheets, made of ink, paper, parchment, or other materials, usually fastened together to hinge at one side. A single sheet within a book is called a leaf, and each side of a leaf is called a page. A book produced in electronic format is known as an electronic book (e-book).

Books may also refer to works of literature, or a main division of such a work. In library and information science, a book is called a monograph, to distinguish it from serial periodicals such as magazines, journals or newspapers. The body of all written works including books is literature. In novels and sometimes other types of books (for example, biographies), a book may be divided into several large sections, also called books (Book 1, Book 2, Book 3, and so on). A lover of books is usually referred to as a bibliophile or, more informally, a bookworm.

A store where books are bought and sold is a bookstore or bookshop. Books can also be borrowed from libraries. In 2010, Google estimated that since the invention of printing, approximately 130,000,000 unique titles had been published.^[1]

Etymology[link]

The word comes from Old English "bōc" which (itself) comes from the Germanic root "*bōk-", cognate to beech.^[2] Similarly, in Slavic languages (for example, Russian, Bulgarian) "буква" (bukva—"letter") is cognate with "beech". In Russian and in Serbian, another Slavic language, the words "букварь" (bukvar') and "буквар" (bukvar), respectively, refer specifically to a primary school textbook that helps young children master the techniques of reading and writing.

It is thus conjectured that the earliest Indo-European writings may have been carved on beech wood.^[3] Similarly, the Latin word codex, meaning a book in the modern sense (bound and with separate leaves), originally meant "block of wood".

History of books[link]

Antiquity[link]

Sumerian language cuneiform script clay tablet, 2400–2200 BC

When writing systems were invented/created in ancient civilizations, nearly everything that could be written upon—stone, clay, tree bark, metal sheets—was used for writing.The study of such inscriptions forms a major part of history.The study of inscriptions is known as epigraphy. Alphabetic writing emerged in Egypt about 5,000 years ago. The Ancient Egyptians would often write on papyrus, a plant grown along the Nile River. At first the words were not separated from each other (scriptural continua) and there was no punctuation. Texts were written from right to left, left to right, and even so that alternate lines read in opposite directions. The technical term for this type of writing is 'boustrophedon,' which means literally 'ox-turning' for the way a farmer drives an ox to plough his fields.

Tablet[link]

A tablet might be defined as a physically robust writing medium, suitable for casual transport and writing. See also stylus.

Clay tablets were just what they sound like: flattened and mostly dry pieces of clay that could be easily carried, and impressed with a ( possible dampened) stylus. They were used as a writing medium, especially for writing in cuneiform, throughout the Bronze Age and well into the Iron Age.

Wax tablets were wooden planks covered in a thick enough coating of wax to record the impressions of a stylus. They were the normal writing material in schools, in accounting, and for taking notes. They had the advantage of being reusable: the wax could be melted, and reformed into a blank. The custom of binding several wax tablets together (Roman pugillares) is a possible precursor for modern books (i.e. codex).^[4] The etymology of the word codex (block of wood) also suggests that it may have developed from wooden wax tablets.^[5]

Scroll[link]

Egyptian papyrus showing the god Osiris and the weighing of the heart.

Papyrus, a thick paper-like material made by weaving the stems of the papyrus plant, then pounding the woven sheet with a hammer-like tool, was used for writing in Ancient Egypt, perhaps as early as the First Dynasty, although the first evidence is from the account books of King Nefertiti Kakai of the Fifth Dynasty (about 2400 BC).^[6] Papyrus sheets were glued together to form a scroll. Tree bark such as lime and other materials were also used.^[7]

According to Herodotus (History 5:58), the Phoenicians brought writing and papyrus to Greece around the 10th or 9th century BC. The Greek word for papyrus as writing material (biblion) and book (biblos) come from the Phoenician port town Byblos, through which papyrus was exported to Greece.^[8] From Greek we also derive the word tome (Greek: τόμος), which originally meant a slice or piece and from there began to denote "a roll of papyrus". Tomus was used by the Latins with exactly the same meaning as volumen (see also below the explanation by Isidore of Seville).

Whether made from papyrus, parchment, or paper, scrolls were the dominant form of book in the Hellenistic, Roman, Chinese, and Hebrew cultures. The more modern codex book format form took over the Roman world by late antiquity, but the scroll format persisted much longer in Asia.

Codex[link]

A Chinese bamboo book meets the modern definition of Codex

In the 5th century, Isidore of Seville explained the then-current relation between codex, book and scroll in his Etymologiae (VI.13): "A codex is composed of many books; a book is of one scroll. It is called codex by way of metaphor from the trunks (codex) of trees or vines, as if it were a wooden stock, because it contains in itself a multitude of books, as it were of branches." Modern usage differs.

A codex (in modern usage) is the first information repository that modern people would recognize as a "book": leaves of uniform size bound in some manner along one edge, and typically held between two covers made of some more robust material. The first written mention of the codex as a form of book is from Martial, in his Apophoreta CLXXXIV at the end of the century, where he praises its compactness. However, the codex never gained much popularity in the pagan Hellenistic world, and only within the Christian community did it gain widespread use.^[9] This change happened gradually during the 3rd and 4th centuries, and the reasons for adopting the codex form of the book are several: the format is more economical, as both sides of the writing material can be used; and it is portable, searchable, and easy to conceal. The Christian authors may also have wanted to distinguish their writings from the pagan texts written on scrolls.

Middle Ages[link]

Manuscripts[link]

Folio 14 recto of the 5th century Vergilius Romanus contains an author portrait of Virgil. Note the bookcase (capsa), reading stand and the text written without word spacing in rustic capitals.

The fall of the Roman Empire in the 5th century A.D. saw the decline of the culture of ancient Rome. Papyrus became difficult to obtain due to lack of contact with Egypt, and parchment, which had been used for centuries, became the main writing material.

Monasteries carried on the Latin writing tradition in the Western Roman Empire. Cassiodorus, in the monastery of Vivarium (established around 540), stressed the importance of copying texts.^[10] St. Benedict of Nursia, in his Regula Monachorum (completed around the middle of the 6th century) later also promoted reading.^[11] The Rule of St. Benedict (Ch. XLVIII), which set aside certain times for reading, greatly influenced the monastic culture of the Middle Ages and is one of the reasons why the clergy were the predominant readers of books. The tradition and style of the Roman Empire still dominated, but slowly the peculiar medieval book culture emerged.

Before the invention and adoption of the printing press, almost all books were copied by hand, which made books expensive and comparatively rare. Smaller monasteries usually had only a few dozen books, medium-sized perhaps a few hundred. By the 9th century, larger collections held around 500 volumes and even at the end of the Middle Ages, the papal library in Avignon and Paris library of Sorbonne held only around 2,000 volumes.^[12]

Burgundian author and scribe Jean Miélot, from his Miracles de Notre Dame, 15th century.

The scriptorium of the monastery was usually located over the chapter house. Artificial light was forbidden for fear it may damage the manuscripts. There were five types of scribes:

• Calligraphers, who dealt in fine book production
• Copyists, who dealt with basic production and correspondence
• Correctors, who collated and compared a finished book with the manuscript from which it had been produced
• Illuminators, who painted illustrations
• Rubricators, who painted in the red letters

The bookmaking process was long and laborious. The parchment had to be prepared, then the unbound pages were planned and ruled with a blunt tool or lead, after which the text was written by the scribe, who usually left blank areas for illustration and rubrication. Finally, the book was bound by the bookbinder.^[13]

Desk with chained books in the Library of Cesena, Italy.

Different types of ink were known in antiquity, usually prepared from soot and gum, and later also from gall nuts and iron vitriol. This gave writing a brownish black color, but black or brown were not the only colors used. There are texts written in red or even gold, and different colors were used for illumination. For very luxurious manuscripts the whole parchment was colored purple, and the text was written on it with gold or silver (for example, Codex Argenteus).^[14]

Irish monks introduced spacing between words in the 7th century. This facilitated reading, as these monks tended to be less familiar with Latin. However, the use of spaces between words did not become commonplace before the 12th century. It has been argued that the use of spacing between words shows the transition from semi-vocalized reading into silent reading.^[15]

The first books used parchment or vellum (calf skin) for the pages. The book covers were made of wood and covered with leather. Because dried parchment tends to assume the form it had before processing, the books were fitted with clasps or straps. During the later Middle Ages, when public libraries appeared, up to 18th century, books were often chained to a bookshelf or a desk to prevent theft. These chained books are called libri catenati.

At first, books were copied mostly in monasteries, one at a time. With the rise of universities in the 13th century, the Manuscript culture of the time led to an increase in the demand for books, and a new system for copying books appeared. The books were divided into unbound leaves (pecia), which were lent out to different copyists, so the speed of book production was considerably increased. The system was maintained by secular stationers guilds, which produced both religious and non-religious material.^[16]

Judaism has kept the art of the scribe alive up to the present. According to Jewish tradition, the Torah scroll placed in a synagogue must be written by hand on parchment, and a printed book would not do, though the congregation may use printed prayer books, and printed copies of the Scriptures are used for study outside the synagogue. A sofer (scribe) is a highly respected member of any observant Jewish community.

Arab printing techniques[link]

This section may contain inappropriate or misinterpreted citations that do not verify the text. Please help improve this article by checking for inaccuracies. (help, talk, get involved!) (September 2010)

Arabs also produced and bound books in the medieval Islamic world, developing advanced techniques in (Arabic calligraphy), miniatures and bookbinding. A number of cities in the medieval Islamic world had book production centers and book markets. Marrakech, Morocco, had a street named Kutubiyyin or book sellers which contained more than 100 bookshops in the 12th century^{[citation needed]}; the famous Koutoubia Mosque is named so because of its location in this street.

The medieval Islamic world also used a method of reproducing reliable copies of a book in large quantities, known as check reading, in contrast to the traditional method of a single scribe producing only a single copy of a single manuscript. In the check reading method, only "authors could authorize copies, and this was done in public sessions in which the copyist read the copy aloud in the presence of the author, who then certified it as accurate."^[17] With this check-reading system, "an author might produce a dozen or more copies from a single reading," and with two or more readings, "more than one hundred copies of a single book could easily be produced."^[18]

Wood block printing[link]

In woodblock printing, a relief image of an entire page was carved into blocks of wood, inked, and used to print copies of that page. This method originated in China, in the Han dynasty (before 220AD), as a method of printing on textiles and later paper, and was widely used throughout East Asia. The oldest dated book printed by this method is The Diamond Sutra (868 AD).

The method (called Woodcut when used in art) arrived in Europe in the early 14th century. Books (known as block-books), as well as playing-cards and religious pictures, began to be produced by this method. Creating an entire book was a painstaking process, requiring a hand-carved block for each page; and the wood blocks tended to crack, if stored for long. The monks or people who wrote them were paid highly.

Movable type and incunabula[link]

A 15th century incunabulum. Notice the blind-tooled cover, corner bosses and clasps.

The Chinese inventor Bi Sheng made movable type of earthenware circa 1045, but there are no known surviving examples of his printing. Around 1450, in what is commonly regarded as an independent invention, Johannes Gutenberg invented movable type in Europe, along with innovations in casting the type based on a matrix and hand mould. This invention gradually made books less expensive to produce, and more widely available.

Early printed books, single sheets and images which were created before 1501 in Europe are known as incunabula. A man born in 1453, the year of the fall of Constantinople, could look back from his fiftieth year on a lifetime in which about eight million books had been printed, more perhaps than all the scribes of Europe had produced since Constantine founded his city in A.D. 330.^[19]

Modern world[link]

Steam-powered printing presses became popular in the early 19th century. These machines could print 1,100 sheets per hour, but workers could only set 2,000 letters per hour.^{[citation needed]}

Monotype and linotype typesetting machines were introduced in the late 19th century. They could set more than 6,000 letters per hour and an entire line of type at once.

The centuries after the 15th century were thus spent on improving both the printing press and the conditions for freedom of the press through the gradual relaxation of restrictive censorship laws. See also intellectual property, public domain, copyright. In mid-20th century, European book production had risen to over 200,000 titles per year.

Book manufacturing in the modern world[link]

This section is too long. Consider either splitting it into new page or sub-sections or summarizing it.

The spine of the book is an important aspect in book design, especially in the cover design. When the books are stacked up or stored in a shelf, the details on the spine is the only visible surface that contains the information about the book. In stores, it is the details on the spine that attract buyers' attention first.

The methods used for the printing and binding of books continued fundamentally unchanged from the 15th century into the early years of the 20th century. While there was of course more mechanization, Gutenberg would have had no difficulty in understanding what was going on if he had visited a book printer in 1900.

Gutenberg's invention was the use of movable metal types, assembled into words, lines, and pages and then printed by letterpress. In letterpress printing ink is spread onto the tops of raised metal type, and is transferred onto a sheet of paper which is pressed against the type. Sheet-fed letterpress printing is still available but tends to be used for collector's books and is now more of an art form than a commercial technique (see Letterpress).

Modern paper books are printed on papers which are designed specifically for the publication of printed books. Traditionally, book papers are off white or low white papers (easier to read), are opaque to minimise the show through of text from one side of the page to the other and are (usually) made to tighter caliper or thickness specifications, particularly for case bound books. Typically, books papers are light weight papers 60 to 90 g/m² and often specified by their caliper/substance ratios (volume basis). For example, a bulky 80 g/m² paper may have a caliper of 120 micrometres (0.12 mm) which would be Volume 15 (120×10/80) whereas a low bulk 80 g/m² may have a caliper of 88 micrometres, giving a volume 11. This volume basis then allows the calculation of a books PPI (printed pages per inch) which is an important factor for the design of book jackets and the binding of the finished book. Different paper qualities are used as book paper depending on type of book: Machine finished coated papers, woodfree uncoated papers, coated fine papers and special fine papers are common paper grades.

Today, the majority of books are printed by offset lithography in which an image of the material to be printed is photographically or digitally transferred to a flexible metal plate where it is developed to exploit the antipathy between grease (the ink) and water. When the plate is mounted on the press, water is spread over it. The developed areas of the plate repel water thus allowing the ink to adhere to only those parts of the plate which are to print. The ink is then offset onto a rubbery blanket (to prevent water from soaking the paper) and then finally to the paper.

When a book is printed the pages are laid out on the plate so that after the printed sheet is folded the pages will be in the correct sequence. Books tend to be manufactured nowadays in a few standard sizes. The sizes of books are usually specified as "trim size": the size of the page after the sheet has been folded and trimmed. Trimming involves cutting approximately 1/8" off top, bottom and fore-edge (the edge opposite to the spine) as part of the binding process to remove the folds so that the pages can be opened. The standard sizes result from sheet sizes (therefore machine sizes) which became popular 200 or 300 years ago, and have come to dominate the industry. The basic standard commercial book sizes in the United States, always expressed as width × height, are: 4¼" × 7" (rack size paperback), 5⅛" × 7⅝" (digest size paperback), 5½" × 8¼", 5½" × 8½", 6⅛" × 9¼", 7" × 10", and 8½" × 11". These "standard" trim sizes will often vary slightly depending on the particular printing presses used, and on the imprecision of the trimming operation. Of course other trim sizes are available, and some publishers favor sizes not listed here which they might nominate as "standard" as well, such as 6" × 9", 8" × 10". In Britain the equivalent standard sizes differ slightly, as well as now being expressed in millimeters, and with height preceding width. Thus the UK equivalent of 6⅛" × 9¼" is 234 × 156 mm. British conventions in this regard prevail throughout the English speaking world, except for USA. The European book manufacturing industry works to a completely different set of standards.

Some books, particularly those with shorter runs (i.e. of which fewer copies are to be made) will be printed on sheet-fed offset presses, but most books are now printed on web presses, which are fed by a continuous roll of paper, and can consequently print more copies in a shorter time. On a sheet-fed press a stack of sheets of paper stands at one end of the press, and each sheet passes through the press individually. The paper will be printed on both sides and delivered, flat, as a stack of paper at the other end of the press. These sheets then have to be folded on another machine which uses bars, rollers and cutters to fold the sheet up into one or more signatures. A signature is a section of a book, usually of 32 pages, but sometimes 16, 48 or even 64 pages. After the signatures are all folded they are gathered: placed in sequence in bins over a circulating belt onto which one signature from each bin is dropped. Thus as the line circulates a complete "book" is collected together in one stack, next to another, and another.

A web press carries out the folding itself, delivering bundles of signatures ready to go into the gathering line. Notice that when the book is being printed it is being printed one (or two) signatures at a time, not one complete book at a time. Thus if there are to be 10,000 copies printed, the press will run 10,000 of the first form (the pages imaged onto the first plate and its back-up plate, representing one or two signatures), then 10,000 of the next form, and so on till all the signatures have been printed. Actually, because there is a known average spoilage rate in each of the steps in the book's progress through the manufacturing system, if 10,000 books are to be made, the printer will print between 10,500 and 11,000 copies so that subsequent spoilage will still allow the delivery of the ordered quantity of books. Sources of spoilage tend to be mainly make-readies.

A make-ready is the preparatory work carried out by the pressmen to get the printing press up to the required quality of impression. Included in make-ready is the time taken to mount the plate onto the machine, clean up any mess from the previous job, and get the press up to speed. The main part of making-ready is however getting the ink/water balance right, and ensuring that the inking is even across the whole width of the paper. This is done by running paper through the press and printing waste pages while adjusting the press to improve quality. Densitometers are used to ensure even inking and consistency from one form to another. As soon as the pressman decides that the printing is correct, all the make-ready sheets will be discarded, and the press will start making books. Similar make readies take place in the folding and binding areas, each involving spoilage of paper.

After the signatures are folded and gathered, they move into the bindery. In the middle of the last century there were still many trade binders – stand-alone binding companies which did no printing, specializing in binding alone. At that time, largely because of the dominance of letterpress printing, the pattern of the industry was for typesetting and printing to take place in one location, and binding in a different factory. When type was all metal, a typical book's worth of type would be bulky, fragile and heavy. The less it was moved in this condition the better: so it was almost invariable that printing would be carried out in the same location as the typesetting. Printed sheets on the other hand could easily be moved. Now, because of the increasing computerization of the process of preparing a book for the printer, the typesetting part of the job has flowed upstream, where it is done either by separately contracting companies working for the publisher, by the publishers themselves, or even by the authors. Mergers in the book manufacturing industry mean that it is now unusual to find a bindery which is not also involved in book printing (and vice versa).

If the book is a hardback its path through the bindery will involve more points of activity than if it is a paperback. A paperback binding line (a number of pieces of machinery linked by conveyor belts) involves few steps. The gathered signatures, book blocks, will be fed into the line where they will one by one be gripped by plates converging from each side of the book, turned spine up and advanced towards a gluing station. En route the spine of the book block will be ground off leaving a roughened edge to the tightly gripped collection of pages. The grinding leaves fibers which will grip onto the glue which is then spread onto the spine of the book. Covers then meet up with the book blocks, and one cover is dropped onto the glued spine of each book block, and is pressed against the spine by rollers. The book is then carried forward to the trimming station, where a three-knife trimmer will simultaneously cut the top and bottom and the fore-edge of the paperback to leave clear square edges. The books are then packed into cartons, or packed on skids, and shipped.

Binding a hardback is more complicated. Look at a hardback book and you will see the cover overlaps the pages by about 1/8" all round. These overlaps are called squares. The blank piece of paper inside the cover is called the endpaper, or endsheet: it is of somewhat stronger paper than the rest of the book as it is the endpapers that hold the book into the case. The endpapers will be tipped to the first and last signatures before the separate signatures are placed into the bins on the gathering line. Tipping involves spreading some glue along the spine edge of the folded endpaper and pressing the endpaper against the signature. The gathered signatures are then glued along the spine, and the book block is trimmed, like the paperback, but will continue after this to the rounder and backer. The book block together with its endpapers will be gripped from the sides and passed under a roller with presses it from side to side, smashing the spine down and out around the sides so that the entire book takes on a rounded cross section: convex on the spine, concave at the fore-edge, with "ears" projecting on either side of the spine. Then the spine is glued again, a paper liner is stuck to it and headbands and footbands are applied. Next a crash lining (an open weave cloth somewhat like a stronger cheesecloth) is usually applied, overlapping the sides of the spine by an inch or more. Finally the inside of the case, which has been constructed and foil-stamped off-line on a separate machine, is glued on either side (but not on the spine area) and placed over the book block. This entire sandwich is now gripped from the outside and pressed together to form a solid bond between the endpapers and the inside of the case. The crash lining, which is glued to the spine of the pages, but not the spine of the case, is held between the endpapers and the case sides, and in fact provides most of the strength holding the book block into the case. The book will then be jacketed (most often by hand, allowing this stage to be an inspection stage also) before being packed ready for shipment.

The sequence of events can vary slightly, and usually the entire sequence does not occur in one continuous pass through a binding line. What has been described above is unsewn binding, now increasingly common. The signatures of a book can also be held together by Smyth sewing. Needles pass through the spine fold of each signature in succession, from the outside to the center of the fold, sewing the pages of the signature together and each signature to its neighbors. McCain sewing, often used in schoolbook binding, involves drilling holes through the entire book and sewing through all the pages from front to back near the spine edge. Both of these methods mean that the folds in the spine of the book will not be ground off in the binding line. This is true of another technique, notch binding, where gashes about an inch long are made at intervals through the fold in the spine of each signature, parallel to the spine direction. In the binding line glue is forced into these "notches" right to the center of the signature, so that every pair of pages in the signature is bonded to every other one, just as in the Smyth sewn book. The rest of the binding process is similar in all instances. Sewn and notch bound books can be bound as either hardbacks or paperbacks.

Making cases happens off-line and prior to the book's arrival at the binding line. In the most basic case making, two pieces of cardboard are placed onto a glued piece of cloth with a space between them into which is glued a thinner board cut to the width of the spine of the book. The overlapping edges of the cloth (about 5/8" all round) are folded over the boards, and pressed down to adhere. After case making the stack of cases will go to the foil stamping area. Metal dies, photoengraved elsewhere, are mounted in the stamping machine and rolls of foil are positioned to pass between the dies and the case to be stamped. Heat and pressure cause the foil to detach from its backing and adhere to the case. Foils come in various shades of gold and silver and in a variety pigment colors, and by careful setup quite elaborate effects can be achieved by using different rolls of foil on the one book. Cases can also be made from paper which has been printed separately and then protected with clear film lamination. A three-piece case is made similarly but has a different material on the spine and overlapping onto the sides: so it starts out as three pieces of material, one each of a cheaper material for the sides and the different, stronger material for the spine.

Recent developments in book manufacturing include the development of digital printing. Book pages are printed, in much the same way as an office copier works, using toner rather than ink. Each book is printed in one pass, not as separate signatures. Digital printing has permitted the manufacture of much smaller quantities than offset, in part because of the absence of make readies and of spoilage. One might think of a web press as printing quantities over 2000, quantities from 250 to 2000 being printed on sheet-fed presses, and digital presses doing quantities below 250. These numbers are of course only approximate and will vary from supplier to supplier, and from book to book depending on its characteristics. Digital printing has opened up the possibility of print-on-demand, where no books are printed until after an order is received from a customer.

Digital format[link]

The term e-book is a contraction of "electronic book"; it refers to a book-length publication in digital form.^[20] An e-book is usually made available through the internet, but also on CD-ROM and other forms. E-Books may be read either via a computer or by means of a portable book display device known as an e-book reader, such as the Sony Reader, Barnes & Noble Nook or the Amazon Kindle. These devices attempt to mimic the experience of reading a print book.

Throughout the 20th century, libraries have faced an ever-increasing rate of publishing, sometimes called an information explosion. The advent of electronic publishing and the Internet means that much new information is not printed in paper books, but is made available online through a digital library, on CD-ROM, or in the form of e-books. An on-line book is an e-book that is available online through the internet.

Though many books are produced digitally, most digital versions are not available to the public, and there is no decline in the rate of paper publishing.^[21] There is an effort, however, to convert books that are in the public domain into a digital medium for unlimited redistribution and infinite availability. This effort is spearheaded by Project Gutenberg combined with Distributed Proofreaders.

There have also been new developments in the process of publishing books. Technologies such as print on demand, which make it possible to print as few as one book at a time, have made self-publishing much easier and more affordable. On-demand publishing has allowed publishers, by avoiding the high costs of warehousing, to keep low-selling books in print rather than declaring them out of print.

Book design[link]

Book design is the art of incorporating the content, style, format, design, and sequence of the various components of a book into a coherent whole.

In the words of Jan Tschichold, book design "though largely forgotten today, methods and rules upon which it is impossible to improve have been developed over centuries. To produce perfect books these rules have to be brought back to life and applied." Richard Hendel describes book design as "an arcane subject" and refers to the need for a context to understand what that means.

Sizes[link]

Real-size facsimile of Codex Gigas

The size of a modern book is based on the printing area of a common flatbed press. The pages of type were arranged and clamped in a frame, so that when printed on a sheet of paper the full size of the press, the pages would be right side up and in order when the sheet was folded, and the folded edges trimmed.

The most common book sizes are:

• Quarto (4to): the sheet of paper is folded twice, forming four leaves (eight pages) approximately 11-13 inches (ca 30 cm) tall
• Octavo (8vo): the most common size for current hardcover books. The sheet is folded three times into eight leaves (16 pages) up to 9 ¾" (ca 23 cm) tall.
• DuoDecimo (12mo): a size between 8vo and 16mo, up to 7 ¾" (ca 18 cm) tall
• Sextodecimo (16mo): the sheet is folded four times, forming 16 leaves (32 pages) up to 6 ¾" (ca 15 cm) tall

Sizes smaller than 16mo are:

• 24mo: up to 5 ¾" (ca 13 cm) tall.
• 32mo: up to 5" (ca 12 cm) tall.
• 48mo: up to 4" (ca 10 cm) tall.
• 64mo: up to 3" (ca 8 cm) tall.

Small books can be called booklets.

Sizes larger than quarto are:

• Folio: up to 15" (ca 38 cm) tall.
• Elephant Folio: up to 23" (ca 58 cm) tall.
• Atlas Folio: up to 25" (ca 63 cm) tall.
• Double Elephant Folio: up to 50" (ca 127 cm) tall.

The largest extant medieval manuscript in the world is Codex Gigas 92 × 50 × 22 cm. The world's largest book made of stone is in Kuthodaw Pagoda (Burma).

The longest book title in the world is 670 words long.

Types of books[link]

Types of books according to their contents[link]

Novels in a Polish bookstore

A common separation by content are fiction and non-fictional books. By no means are books limited to this classification, but it is a separation that can be found in most collections, libraries, and bookstores.

Fiction[link]

Many of the books published today are fictitious stories. They are in-part or completely untrue or fantasy. Historically, paper production was considered too expensive to be used for entertainment. An increase in global literacy and print technology led to the increased publication of books for the purpose of entertainment, and allegorical social commentary. Most fiction is additionally categorized by genre.

The novel is the most common form of fictional book. Novels are stories that typically feature a plot, setting, themes and characters. Stories and narrative are not restricted to any topic; a novel can be whimsical, serious or controversial. The novel has had a tremendous impact on entertainment and publishing markets.^[22] A novella is a term sometimes used for fictional prose typically between 17,500 and 40,000 words, and a novelette between 7,500 and 17,500. A Short story may be any length up to 10,000 words, but these word lengths are not universally established.

Comic books or graphic novels are books in which the story is illustrated. The characters and narrators use speech or thought bubbles to express verbal language.

Non-fiction[link]

A page from a dictionary

In a library, a reference book is a general type of non-fiction book which provides information as opposed to telling a story, essay, commentary, or otherwise supporting a point of view. An almanac is a very general reference book, usually one-volume, with lists of data and information on many topics. An encyclopedia is a book or set of books designed to have more in-depth articles on many topics. A book listing words, their etymology, meanings, and other information is called a dictionary. A book which is a collection of maps is an atlas. A more specific reference book with tables or lists of data and information about a certain topic, often intended for professional use, is often called a handbook. Books which try to list references and abstracts in a certain broad area may be called an index, such as Engineering Index, or abstracts such as chemical abstracts and biological abstracts.

An atlas

Books with technical information on how to do something or how to use some equipment are called instruction manuals. Other popular how-to books include cookbooks and home improvement books.

Students typically store and carry textbooks and schoolbooks for study purposes. Elementary school pupils often use workbooks, which are published with spaces or blanks to be filled by them for study or homework. In US higher education, it is common for a student to take an exam using a blue book.

A page from a notebook used as hand written diary

There is a large set of books that are made only to write private ideas, notes, and accounts. These books are rarely published and are typically destroyed or remain private. Notebooks are blank papers to be written in by the user. Students and writers commonly use them for taking notes. Scientists and other researchers use lab notebooks to record their notes. They often feature spiral coil bindings at the edge so that pages may easily be torn out.

A Telephone Directory, with business and residence listings.

Address books, phone books, and calendar/appointment books are commonly used on a daily basis for recording appointments, meetings and personal contact information.

Books for recording periodic entries by the user, such as daily information about a journey, are called logbooks or simply logs. A similar book for writing the owner's daily private personal events, information, and ideas is called a diary or personal journal.

Businesses use accounting books such as journals and ledgers to record financial data in a practice called bookkeeping.

Other types[link]

There are several other types of books which are not commonly found under this system. Albums are books for holding a group of items belonging to a particular theme, such as a set of photographs, card collections, and memorabilia. One common example is stamp albums, which are used by many hobbyists to protect and organize their collections of postage stamps. Such albums are often made using removable plastic pages held inside in a ringed binder or other similar smolder. Picture books children's books with little text and pictures on every page

Hymnals are books with collections of musical hymns that can typically be found in churches. Prayerbooks or missals are books that contain written prayers and are commonly carried by monks, nuns, and other devoted followers or clergy.

Types of books according to their binding or cover[link]

Hardcover books

Paperback books

Hardcover books have a stiff binding. Paperback books have cheaper, flexible covers which tend to be less durable. An alternative to paperback is the glossy cover, otherwise known as a dust cover, found on magazines, and comic books. Spiral-bound books are bound by spirals made of metal or plastic. Examples of spiral-bound books include: teachers' manuals and puzzle books (crosswords, sudoku).

Publishing is a process for producing pre-printed books, magazines, and newspapers for the reader/user to buy.

Publishers may produce low-cost, pre-publication copies known as galleys or 'bound proofs' for promotional purposes, such as generating reviews in advance of publication. Galleys are usually made as cheaply as possible, since they are not intended for sale.

Collections of books[link]

Celsus Library was built in 135 AD and could house around 12,000 scrolls.

Private or personal libraries made up of non-fiction and fiction books, (as opposed to the state or institutional records kept in archives) first appeared in classical Greece. In ancient world the maintaining of a library was usually (but not exclusively) the privilege of a wealthy individual. These libraries could have been either private or public, i.e. for people who were interested in using them. The difference from a modern public library lies in the fact that they were usually not funded from public sources. It is estimated that in the city of Rome at the end of the 3rd century there were around 30 public libraries. Public libraries also existed in other cities of the ancient Mediterranean region (for example, Library of Alexandria).^[23] Later, in the Middle Ages, monasteries and universities had also libraries that could be accessible to general public. Typically not the whole collection was available to public, the books could not be borrowed and often were chained to reading stands to prevent theft.

The beginning of modern public library begins around 15th century when individuals started to donate books to towns.^[24] The growth of a public library system in the United States started in the late 19th century and was much helped by donations from Andrew Carnegie. This reflected classes in a society: The poor or the middle class had to access most books through a public library or by other means while the rich could afford to have a private library built in their homes. In the United States the Boston Public Library 1852 Report of the Trustees established the justification for the public library as a tax-supported institution intended to extend educational opportunity and provide for general culture.^[25]

The advent of paperback books in the 20th century led to an explosion of popular publishing. Paperback books made owning books affordable for many people. Paperback books often included works from genres that had previously been published mostly in pulp magazines. As a result of the low cost of such books and the spread of bookstores filled with them (in addition to the creation of a smaller market of extremely cheap used paperbacks) owning a private library ceased to be a status symbol for the rich.

In library and booksellers' catalogues, it is common to include an abbreviation such as "Crown 8vo" to indicate the paper size from which the book is made.

When rows of books are lined on a book holder, bookends are sometimes needed to keep them from slanting.

Identification and classification[link]

During the 20th century, librarians were concerned about keeping track of the many books being added yearly to the Gutenberg Galaxy. Through a global society called the International Federation of Library Associations and Institutions (IFLA), they devised a series of tools including the International Standard Bibliographic Description (ISBD).

ISBN with barcode

Each book is specified by an International Standard Book Number, or ISBN, which is unique to every edition of every book produced by participating publishers, world wide. It is managed by the ISBN Society. An ISBN has four parts: the first part is the country code, the second the publisher code, and the third the title code. The last part is a check digit, and can take values from 0–9 and X (10). The EAN Barcodes numbers for books are derived from the ISBN by prefixing 978, for Bookland, and calculating a new check digit.

Commercial publishers in industrialized countries generally assign ISBNs to their books, so buyers may presume that the ISBN is part of a total international system, with no exceptions. However, many government publishers, in industrial as well as developing countries, do not participate fully in the ISBN system, and publish books which do not have ISBNs.

A large or public collection requires a catalogue. Codes called "call numbers" relate the books to the catalogue, and determine their locations on the shelves. Call numbers are based on a Library classification system. The call number is placed on the spine of the book, normally a short distance before the bottom, and inside.

Institutional or national standards, such as ANSI/NISO Z39.41 - 1997, establish the correct way to place information (such as the title, or the name of the author) on book spines, and on "shelvable" book-like objects, such as containers for DVDs, video tapes and software.

Books on library shelves with bookends, and call numbers visible on the spines

One of the earliest and most widely known systems of cataloguing books is the Dewey Decimal System. Another widely known system is the Library of Congress Classification system. Both systems are biased towards subjects which were well-represented in US libraries when they were developed, and hence have problems handling new subjects, such as computing, or subjects relating to other cultures.^{[citation needed]}

Information about books and authors can be stored in databases like online general-interest book databases.

Metadata about a book may include its ISBN or other classification number (see above), the names of contributors (author, editor, illustrator) and publisher, its date and size, and the language of the text.

Classification systems[link]

• Bliss bibliographic classification (BC)
• Chinese Library Classification (CLC)
• Colon Classification
• Dewey Decimal Classification (DDC)
• Harvard-Yenching Classification
• Library of Congress Classification (LCC)
• New Classification Scheme for Chinese Libraries
• Universal Decimal Classification (UDC)

Uses for books[link]

Aside from the primary purpose of reading them, books are also used for other ends:

• A book can be an artistic artifact, a piece of art; this is sometimes known as an artists' book.
• A book may be evaluated by a reader or professional writer to create a book review.
• A book may be read by a group of people to use as a spark for social or academic discussion, as in a book club.
• A book may be studied by students as the subject of a writing and analysis exercise in the form of a book report.
• Books are sometimes used for their exterior appearance to decorate a room, such as a study.

Paper and conservation issues[link]

Halfbound book with leather and marbled paper.

Though papermaking in Europe had begun around the 11th century, up until the beginning of 16th century vellum and paper were produced congruent to one another, vellum being the more expensive and durable option. Printers or publishers would often issue the same publication on both materials, to cater to more than one market.

Paper was first made in China, as early as 200 B.C., and reached Europe through Muslim territories. At first made of rags, the industrial revolution changed paper-making practices, allowing for paper to be made out of wood pulp.

Paper made from wood pulp became popular in the early 20th century, because it was cheaper than linen or abaca cloth-based papers. Pulp-based paper made books less expensive to the general public. This paved the way for huge leaps in the rate of literacy in industrialised nations, and enabled the spread of information during the Second Industrial Revolution.

However pulp paper contained acid, that eventually destroys the paper from within. Earlier techniques for making paper used limestone rollers, which neutralized the acid in the pulp. Books printed between 1850 and 1950 are at risk; more recent books are often printed on acid-free or alkaline paper. Libraries today have to consider mass deacidification of their older collections.

Stability of the climate is critical to the long-term preservation of paper and book material.^[26] Good air circulation is important to keep fluctuation in climate stable. The HVAC system should be up to date and functioning efficiently. Light is detrimental to collections. Therefore, care should be given to the collections by implementing light control. General housekeeping issues can be addressed, including pest control. In addition to these helpful solutions, a library must also make an effort to be prepared if a disaster occurs, one that they cannot control. Time and effort should be given to create a concise and effective disaster plan to counteract any damage incurred through "acts of god" therefore an emergency management plan should be in place.

See also[link]

References[link]

External links[link]

Wikibooks has more on the topic of Book

Look up book in Wiktionary, the free dictionary.

Find more about Book on Wikipedia's sister projects:
	Definitions and translations from Wiktionary
	Images and media from Commons
	Learning resources from Wikiversity
	News stories from Wikinews
	Quotations from Wikiquote
	Source texts from Wikisource
	Textbooks from Wikibooks

• Centre for the History of the Book
• Manuscripts, Books, and Maps: The Printing Press and a Changing World
• Society for the History of Authorship, Reading and Publishing
• Old Books, How to find information on publication history and value (1998) Smithsonian Institution Libraries

lez:Улуб

Domestic dog Temporal range: 0.015–0 Ma PreЄ Є O S D C P T J K Pg N ↓ Pleistocene – Recent
Yellow Labrador Retriever, the most registered breed of 2009 with the AKC More images of dogs.
Conservation status
Domesticated
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	Canidae
Genus:	Canis
Species:	C. lupus
Subspecies:	C. l. familiaris[1]
Trinomial name
Canis lupus familiaris[2]
Synonyms
Species synonymy aegyptius Linnaeus, 1758 alco C. E. H. Smith, 1839 americanus Gmelin, 1792 anglicus Gmelin, 1792 antarcticus Gmelin, 1792 aprinus Gmelin, 1792 aquaticus Linnaeus, 1758 aquatilis Gmelin, 1792 avicularis Gmelin, 1792 borealis C. E. H. Smith, 1839 brevipilis Gmelin, 1792 cursorius Gmelin, 1792 domesticus Linnaeus, 1758 extrarius Gmelin, 1792 ferus C. E. H. Smith, 1839 fricator Gmelin, 1792 fricatrix Linnaeus, 1758 fuillus Gmelin, 1792 gallicus Gmelin, 1792 glaucus C. E. H. Smith, 1839 graius Linnaeus, 1758 grajus Gmelin, 1792 hagenbecki Krumbiegel, 1950 haitensis C. E. H. Smith, 1839 hibernicus Gmelin, 1792 hirsutus Gmelin, 1792 hybridus Gmelin, 1792 islandicus Gmelin, 1792 italicus Gmelin, 1792 laniarius Gmelin, 1792 leoninus Gmelin, 1792 leporarius C. E. H. Smith, 1839 major Gmelin, 1792 mastinus Linnaeus, 1758 melitacus Gmelin, 1792 melitaeus Linnaeus, 1758 minor Gmelin, 1792 molossus Gmelin, 1792 mustelinus Linnaeus, 1758 obesus Gmelin, 1792 orientalis Gmelin, 1792 pacificus C. E. H. Smith, 1839 plancus Gmelin, 1792 pomeranus Gmelin, 1792 sagaces C. E. H. Smith, 1839 sanguinarius C. E. H. Smith, 1839 sagax Linnaeus, 1758 scoticus Gmelin, 1792 sibiricus Gmelin, 1792 suillus C. E. H. Smith, 1839

The domestic dog (Canis lupus familiaris),^[2][3] is a subspecies of the gray wolf (Canis lupus), a member of the Canidae family of the mammilian order Carnivora. The term "domestic dog" is generally used for both domesticated and feral varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in human history. The word "dog" may also mean the male of a canine species,^[4] as opposed to the word "bitch" for the female of the species.

The present lineage of dogs was domesticated from gray wolves about 15,000 years ago.^[5] Remains of domesticated dogs have been found in Siberia and Belgium from about 33,000 years ago. None of these early domestication lineages seem to have survived the Last Glacial Maximum. Although mDNA suggest a split between dogs and wolves around 100,000 years ago no specimens predate 33,000 years ago that are clearly morphologically domesticated dog.^[6][7][8]

Dogs' value to early human hunter-gatherers led to them quickly becoming ubiquitous across world cultures. Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship, and, more recently, aiding handicapped individuals. This impact on human society has given them the nickname "Man's Best Friend" in the Western world. In some cultures, dogs are also source of meat.^[9][10] In 2001, there were estimated to be 400 million dogs in the world.^[11]

Most breeds of dogs are at most a few hundred years old, having been artificially selected for particular morphologies and behaviors by people for specific functional roles. Through this selective breeding, the dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal.^[12] For example, height measured to the withers ranges from a 2 inches (51 mm) in the Chihuahua to a 2 feet (0.61 m) in the Irish Wolfhound; color varies from white through grays (usually called "blue") to black, and browns from light (tan) to dark ("red" or "chocolate") in a wide variation of patterns; coats can be short or long, coarse-haired to wool-like, straight, curly, or smooth.^[13] It is common for most breeds to shed this coat.

Etymology and related terminology[link]

Dog is the common use term that refers to members of the subspecies Canis lupus familiaris (canis, "dog"; lupus, "wolf"; familiaris, "of a household" or "domestic"). The term can also be used to refer to a wider range of related species, such as the members of the genus Canis, or "true dogs", including the wolf, coyote, and jackals; or it can refer to the members of the tribe Canini, which would also include the African wild dog; or it can be used to refer to any member of the family Canidae, which would also include the foxes, bush dog, raccoon dog, and others.^[14] Some members of the family have "dog" in their common names, such as the raccoon dog and the African wild dog. A few animals have "dog" in their common names but are not canids, such as the prairie dog.

The English word dog comes from Middle English dogge, from Old English docga, a "powerful dog breed".^[15] The term may derive from Proto-Germanic *dukkōn, represented in Old English finger-docce ("finger-muscle").^[16] The word also shows the familiar petname diminutive -ga also seen in frogga "frog", picga "pig", stagga "stag", wicga "beetle, worm", among others.^[17] Due to the archaic structure of the word, the term dog may ultimately derive from the earliest layer of Proto-Indo-European vocabulary, reflecting the role of the dog as the earliest domesticated animal.^[18]

In 14th-century England, hound (from Old English: hund) was the general word for all domestic canines, and dog referred to a subtype of hound, a group including the mastiff. It is believed this "dog" type of "hound" was so common it eventually became the prototype of the category “hound”.^[19] By the 16th century, dog had become the general word, and hound had begun to refer only to types used for hunting.^[20] Hound, cognate to German Hund, Dutch hond, common Scandinavian hund, and Icelandic hundur, is ultimately derived from the Proto-Indo-European *kwon- "dog", found in Welsh ci (plural cwn), Latin canis, Greek kýōn, Lithuanian šuõ.^[21]

In breeding circles, a male canine is referred to as a dog, while a female is called a bitch (Middle English bicche, from Old English bicce, ultimately from Old Norse bikkja). A group of offspring is a litter. The father of a litter is called the sire, and the mother is called the dam. Offspring are, in general, called pups or puppies, from French poupée, until they are about a year old. The process of birth is whelping, from the Old English word hwelp (cf. German Welpe, Dutch welp, Swedish valpa, Icelandic hvelpur).^[22]

Taxonomy[link]

In 1753, the father of modern biological taxonomy, Carl Linnaeus, listed among the types of quadruped familiar to him, the Latin word for dog, “Canis.” Among the species within this genus, Linnaeus listed the fox, as "Canis vulpes", wolves (Canis lupus), and the domestic dog, (Canis canis; see File:Linnaeus - Regnum Animale (1735).png).

In later editions, Linnaeus dropped "Canis canis" and greatly expanded his list of the Canis genus of quadrupeds, and by 1758 included alongside the foxes, wolves, and jackels and many more terms that are now listed as synonyms for domestic dog, including ‘’aegyptius” (hairless dog), ‘’aquaticus’’, (water dog), and ‘’mustelinus’’ (literally “badger dog).” Among these were two that later experts have been widely used for domestic dogs as a species: ‘’Canis domesticus’’ and, most predominantly, ‘’Canis familiaris”, the “common” or “familiar” dog.^[23]

The domestic dog was accepted as a species in its own right until overwhelming evidence from behavior, vocalizations, morphology, and molecular biology led to the contemporary scientific understanding that a single species, the gray wolf, is the common ancestor for all breeds of domestic dogs.^[24][25][26] In recognition of this fact, the domestic dog was reclassified in 1993 as Canis lupus familiaris, a subspecies of the gray wolf Canis lupus, by the Smithsonian Institution and the American Society of Mammalogists. Canis lupus familiaris is listed as the name for the taxon that is broadly used in the scientific community and recommended by ITIS although Canis familiaris, however, is a recognised synonym.^[27]

Since that time, domesticus and all taxa referring to domestic dogs or subspecies of dog listed by Linnaeus, Johann Friedrich Gmelin in 1792, and Christian Smith in 1839, lost their subspecies status and have been listed as taxonomic synonyms for Canis lupus familiaris ^[28]

History and evolution[link]

Ancient Greek rhyton in the shape of a dog's head, made by Brygos, early 5th century BC. Jérôme Carcopino Museum, Department of Archaeology, Aleria

Domestic dogs inherited complex behaviors from their wolf ancestors, which would have been pack hunters with complex body language. These sophisticated forms of social cognition and communication may account for their trainability, playfulness, and ability to fit into human households and social situations, and these attributes have given dogs a relationship with humans that has enabled them to become one of the most successful species on the planet today.^[24]

Although experts largely disagree over the details of dog domestication, it is agreed that human interaction played a significant role in shaping the subspecies.^[29] Domestication may have occurred initially in separate areas particularly Siberia and Europe. Currently it is thought domestication of our current lineage of dog occurred sometime as early as 15,000 years ago and arguably as late as 8500 years ago. Shortly after the latest domestication, dogs became ubiquitous in human populations, and spread throughout the world.

Emigrants from Siberia likely crossed the Bering Strait with dogs in their company, and some experts^[who?] suggest the use of sled dogs may have been critical to the success of the waves that entered North America roughly 12,000 years ago,^{[citation needed]} although the earliest archaeological evidence of dog-like canids in North America dates from about 9,000 years ago.^[30] Dogs were an important part of life for the Athabascan population in North America, and were their only domesticated animal. Dogs also carried much of the load in the migration of the Apache and Navajo tribes 1,400 years ago. Use of dogs as pack animals in these cultures often persisted after the introduction of the horse to North America.^{[31][page needed]}

The current consensus among biologists and archaeologists is that the dating of first domestication is indeterminate,^[29][31] although more recent evidence shows isolated domestication events as early as 33,000 years ago.^[32][33] There is conclusive evidence the present lineage of dogs genetically diverged from their wolf ancestors at least 15,000 years ago,^[5][34][35] but some believe domestication to have occurred earlier.^[29] Evidence is accruing that there were previous domestication events, but that those lineages died out.^[7]

It is not known whether humans domesticated the wolf as such to initiate dog's divergence from its ancestors, or whether dog's evolutionary path had already taken a different course prior to domestication. For example, it is hypothesized that some wolves gathered around the campsites of paleolithic camps to scavenge refuse, and associated evolutionary pressure developed that favored those who were less frightened by, and keener in approaching, humans.

Tesem, an old Egyptian sighthound-like dog.

The bulk of the scientific evidence for the evolution of the domestic dog stems from morphological studies of archaeological findings and mitochondrial DNA studies. The divergence date of roughly 15,000 years ago is based in part on archaeological evidence that demonstrates the domestication of dogs occurred more than 15,000 years ago,^[24][31] and some genetic evidence indicates the domestication of dogs from their wolf ancestors began in the late Upper Paleolithic close to the Pleistocene/Holocene boundary, between 17,000 and 14,000 years ago.^[36] But there is a wide range of other, contradictory findings that make this issue controversial.^{[citation needed]} There are findings beginning currently at 33,000 years ago distinctly placing them as domesticated dogs evidenced not only by shortening of the muzzle but widening as well as crowding of teeth.

Archaeological evidence suggests the latest dogs could have diverged from wolves was roughly 15,000 years ago, although it is possible they diverged much earlier.^[24] In 2008, a team of international scientists released findings from an excavation at Goyet Cave in Belgium declaring a large, toothy canine existed 31,700 years ago and ate a diet of horse, musk ox and reindeer.^[37]

Prior to this Belgian discovery, the earliest dog fossils were two large skulls from Russia and a mandible from Germany dated from roughly 14,000 years ago.^[5][24] Remains of smaller dogs from Natufian cave deposits in the Middle East, including the earliest burial of a human being with a domestic dog, have been dated to around 10,000 to 12,000 years ago.^[5][38] There is a great deal of archaeological evidence for dogs throughout Europe and Asia around this period and through the next two thousand years (roughly 8,000 to 10,000 years ago), with fossils uncovered in Germany, the French Alps, and Iraq, and cave paintings in Turkey.^[24] The oldest remains of a domesticated dog in the Americas were found in Texas and have been dated to about 9,400 years ago.^[39]

DNA studies[link]

DNA studies have provided a wide range of possible divergence dates, from 15,000 to 40,000 years ago,^[5] to as much as 100,000 to 140,000 years ago.^[40] These results depend on a number of assumptions.^[24] Genetic studies are based on comparisons of genetic diversity between species, and depend on a calibration date. Some estimates of divergence dates from DNA evidence use an estimated wolf-coyote divergence date of roughly 700,000 years ago as a calibration.^[41] If this estimate is incorrect, and the actual wolf-coyote divergence is closer to one or two million years ago, or more,^[42] then the DNA evidence that supports specific dog-wolf divergence dates would be interpreted very differently.

Furthermore, it is believed the genetic diversity of wolves has been in decline for the last 200 years, and that the genetic diversity of dogs has been reduced by selective breeding. This could significantly bias DNA analyses to support an earlier divergence date. The genetic evidence for the domestication event occurring in East Asia is also subject to violations of assumptions. These conclusions are based on the location of maximal genetic divergence, and assume hybridization does not occur, and that breeds remain geographically localized. Although these assumptions hold for many species, there is good reason to believe that they do not hold for canines.^[24]

Genetic analyses indicate all dogs are likely descended from a handful of domestication events with a small number of founding females,^[24][36] although there is evidence domesticated dogs interbred with local populations of wild wolves on several occasions.^[5] Data suggest dogs first diverged from wolves in East Asia, and these domesticated dogs then quickly migrated throughout the world, reaching the North American continent around 8000 BC.^[5] The oldest groups of dogs, which show the greatest genetic variability and are the most similar to their wolf ancestors, are primarily Asian and African breeds, including the Basenji, Lhasa Apso, and Siberian Husky.^[43] Some breeds thought to be very old, such as the Pharaoh Hound, Ibizan Hound, and Norwegian Elkhound, are now known to have been created more recently.^[43]

There is a great deal of controversy surrounding the evolutionary framework for the domestication of dogs.^[24] Although it is widely claimed that "man domesticated the wolf,"^[44] man may not have taken such a proactive role in the process.^[24] The nature of the interaction between man and wolf that led to domestication is unknown and controversial. At least three early species of the Homo genus began spreading out of Africa roughly 400,000 years ago, and thus lived for a considerable time in contact with canine species.^[24]

Despite this, there is no evidence of any adaptation of canine species to the presence of the close relatives of modern man. If dogs were domesticated, as believed, roughly 15,000 years ago, the event (or events) would have coincided with a large expansion in human territory and the development of agriculture. This has led some biologists to suggest one of the forces that led to the domestication of dogs was a shift in human lifestyle in the form of established human settlements. Permanent settlements would have coincided with a greater amount of disposable food and would have created a barrier between wild and anthropogenic canine populations.^[24]

Roles with humans[link]

A Siberian Husky used as a pack animal

Early roles[link]

Wolves, and their dog descendants, would have derived significant benefits from living in human camps—more safety, more reliable food, lesser caloric needs, and more chance to breed.^[45] They would have benefited from humans’ upright gait that gives them larger range over which to see potential predators and prey, as well as color vision that, at least by day, gives humans better visual discrimination.^[45] Camp dogs would also have benefitted from human tool use, as in bringing down larger prey and controlling fire for a range of purposes.^[45]

Humans would also have derived enormous benefit from the dogs associated with their camps.^[46] For instance, dogs would have improved sanitation by cleaning up food scraps.^[46] Dogs may have provided warmth, as referred to in the Australian Aboriginal expression “three dog night” (an exceptionally cold night), and they would have alerted the camp to the presence of predators or strangers, using their acute hearing to provide an early warning.^[46]

Anthropologists believe the most significant benefit would have been the use of dogs' sensitive sense of smell to assist with the hunt.^[46] The relationship between the presence of a dog and success in the hunt is often mentioned as a primary reason for the domestication of the wolf, and a 2004 study of hunter groups with and without a dog gives quantitative support to the hypothesis that the benefits of cooperative hunting was an important factor in wolf domestication.^[47]

The cohabitation of dogs and humans would have greatly improved the chances of survival for early human groups, and the domestication of dogs may have been one of the key forces that led to human success.^[48]

A British Bulldog shares a day at the park.

As pets[link]

"The most widespread form of interspecies bonding occurs between humans and dogs"^[46] and the keeping of dogs as companions, particularly by elites, has a long history.^[49] However, pet dog populations grew significantly after World War II as suburbanization increased.^[49] In the 1950s and 1960s, dogs were kept outside more often than they tend to be today ^[50] (using the expression “in the doghouse” to describe exclusion from the group signifies the distance between the doghouse and the home) and were still primarily functional, acting as a guard, children’s playmate, or walking companion. From the 1980s, there have been changes in the role of the pet dog, such as the increased role of dogs in the emotional support of their owners.^[51] People and dogs have become increasingly integrated and implicated in each other’s lives,^[52] to the point where pet dogs actively shape the way a family and home are experienced.^[53]

There have been two major trends in the changing status of pet dogs. The first has been the ‘commodification’ of the dog, shaping it to conform to human expectations of personality and behaviour.^[53] The second has been the broadening of the concept of the family and the home to include dogs-as-dogs within everyday routines and practices.^[53]

There are a vast range of commodity forms available to transform a pet dog into an ideal companion.^[54] The list of goods, services and places available is enormous: from dog perfumes, couture, furniture and housing, to dog groomers, therapists, trainers and care-takers, dog cafes, spas, parks and beaches, and dog hotels, airlines and cemeteries.^[54] While dog training as an organized activity can be traced back to the 18th century, in the last decades of the 20th century it became a high profile issue as many normal dog behaviors such as barking, jumping up, digging, rolling in dung, fighting, and urine marking became increasingly incompatible with the new role of a pet dog.^[55] Dog training books, classes and television programs proliferated as the process of commodifying the pet dog continued.^[56]

A pet dog taking part in Christmas traditions

The majority of contemporary dog owners describe their dog as part of the family,^[53] although some ambivalence about the relationship is evident in the popular reconceptualisation of the dog-human family as a pack.^[53] A dominance model of dog-human relationships has been promoted by some dog trainers, such as on the television program Dog Whisperer. However it has been disputed that "trying to achieve status" is characteristic of dog–human interactions.^[57] Pet dogs play an active role in family life; for example, a study of conversations in dog-human families showed how family members use the dog as a resource, talking to the dog, or talking through the dog, to mediate their interactions with each other.^[58]

Another study of dogs’ roles in families showed many dogs have set tasks or routines undertaken as family members, the most common of which was helping with the washing-up by licking the plates in the dishwasher, and bringing in the newspaper from the lawn.^[53] Increasingly, human family members are engaging in activities centred on the perceived needs and interests of the dog, or in which the dog is an integral partner, such as Dog Dancing and Doga.^[54]

According to the statistics published by the American Pet Products Manufacturers Association in the National Pet Owner Survey in 2009–2010, it is estimated there are 77.5 million dog owners in the United States.^[59] The same survey shows nearly 40% of American households own at least one dog, of which 67% own just one dog, 25% two dogs and nearly 9% more than two dogs. There does not seem to be any gender preference among dogs as pets, as the statistical data reveal an equal number of female and male dog pets. Yet, although several programs are undergoing to promote pet adoption, less than a fifth of the owned dogs come from a shelter.

Work[link]

Dogs have lived and worked with humans in so many roles that they have earned the unique nickname, "man's best friend",^[60] a phrase used in other languages as well. They have been bred for herding livestock,^[61] hunting (e.g. pointers and hounds),^[62] rodent control,^[3] guarding, helping fishermen with nets, detection dogs, and pulling loads, in addition to their roles as companions.^[3]

Book of the Hunt, Gaston III, Count of Foix, 1387–88.

Service dogs such as guide dogs, utility dogs, assistance dogs, hearing dogs, and psychological therapy dogs provide assistance to individuals with physical or mental disabilities.^[63][64] Some dogs owned by epileptics have been shown to alert their handler when the handler shows signs of an impending seizure, sometimes well in advance of onset, allowing the owner to seek safety, medication, or medical care.^[65]

Dogs included in human activities in terms of helping out humans are usually called working dogs. Dogs of several breeds are considered working dogs. Some working dog breeds include Akita, Alaskan Malamute, Anatolian Shepherd Dog, Bernese Mountain Dog, Black Russian Terrier, Boxer, Bullmastiff, Doberman Pinscher, Dogue de Bordeaux, German Pinscher, German Shepherd,^[66] Giant Schnauzer, Great Dane, Great Pyrenees, Great Swiss Mountain Dog, Komondor, Kuvasz, Mastiff, Neapolitan Mastiff, Newfoundland, Portuguese Water Dog, Rottweiler, Saint Bernard, Samoyed, Siberian Husky, Standard Schnauzer, and Tibetan Mastiff.

Sports and shows[link]

Owners of dogs often enter them in competitions^[67] such as breed conformation shows or sports, including racing and sledding.

In conformation shows, also referred to as breed shows, a judge familiar with the specific dog breed evaluates individual purebred dogs for conformity with their established breed type as described in the breed standard. As the breed standard only deals with the externally observable qualities of the dog (such as appearance, movement, and temperament), separately tested qualities (such as ability or health) are not part of the judging in conformation shows.

As a food source[link]

Fried dog meat offered as speciality, among lamb and fish. Shaoyang, Hunan Province, China

Dog meat is consumed in some East Asian countries, including Korea, China, and Vietnam, a practice that dates back to antiquity.^[68] It is estimated that 13–16 million dogs are killed and consumed in Asia every year.^[69] The BBC claims that, in 1999, more than 6,000 restaurants served soups made from dog meat in South Korea.^[70] In Korea, the primary dog breed raised for meat, the nureongi (누렁이), differs from those breeds raised for pets that Koreans may keep in their homes.^[71]

The most popular Korean dog dish is gaejang-guk (also called bosintang), a spicy stew meant to balance the body's heat during the summer months; followers of the custom claim this is done to ensure good health by balancing one's gi, or vital energy of the body. A 19th century version of gaejang-guk explains that the dish is prepared by boiling dog meat with scallions and chili powder. Variations of the dish contain chicken and bamboo shoots. While the dishes are still popular in Korea with a segment of the population, dog is not as widely consumed as beef, chicken, and pork.^[72]

Other cultures, such as Polynesia and pre-Columbian Mexico, also consumed dog meat in their history. However, Western, South Asian, African, and Middle Eastern cultures, in general, regard consumption of dog meat as taboo. In some places, however, such as in rural areas of Poland, dog fat is believed to have medicinal properties—being good for the lungs for instance.^[73]

A CNN report in China dated March 2010 interviews a dog meat vendor who states that most of the dogs that are available for selling to restaurant are raised in special farms but that there is always a chance that a sold dog is someone's lost pet, although dog pet breeds are not considered edible.^[74]

Health risks to humans[link]

It is estimated that two percent of the US population, 4.7 million people, are bitten each year.^[75] In the 1980s and 1990s the US averaged 17 fatalities per year, while in the 2000s this has increased to 26.^[76] 77% of dog bites are from the pet of family or friends, and 50% of attacks occur on the dog owner's property.^[76]

A Colorado study found bites in children were less severe than bites in adults.^[77] The incidence of dog bites in the U.S. is 12.9 per 10,000 inhabitants, but for boys aged 5 to 9, the incidence rate is 60.7 per 10,000. Moreover, children have a much higher chance to be bitten in the face or neck.^[78] Sharp claws with powerful muscles behind them can lacerate flesh in a scratch that can lead to serious infections.^[79]

In the UK between 2003 and 2004, there were 5,868 dog attacks on humans, resulting in 5,770 working days lost in sick leave.^[80]

In the United States, cats and dogs are a factor in more than 86,000 falls each year.^[81] It has been estimated around 2% of dog-related injuries treated in UK hospitals are domestic accidents. The same study found that while dog involvement in road traffic accidents was difficult to quantify, dog-associated road accidents involving injury more commonly involved two-wheeled vehicles.^[82]

Toxocara canis (dog roundworm) eggs in dog feces can cause toxocariasis. In the United States, about 10,000 cases of Toxocara infection are reported in humans each year, and almost 14% of the U.S. population is infected.^[83] In Great Britain, 24% of soil samples taken from public parks contained T. canis eggs.^[84] Untreated toxocariasis can cause retinal damage and decreased vision.^[84] Dog feces can also contain hookworms that cause cutaneous larva migrans in humans.^{[85][86][87][88]}

Health benefits for humans[link]

A human cuddles a Doberman puppy.

A growing body of research indicates the companionship of a dog can enhance human physical health and psychological wellbeing.^[89] Dog and cat owners have been shown to have better mental and physical health than nonowners, making fewer visits to the doctor and being less likely to be on medication than nonowners.^[90] In one study, new pet owners reported a highly significant reduction in minor health problems during the first month following pet acquisition, and this effect was sustained in dog owners through to the end of the study.^[91]

In addition, dog owners took considerably more physical exercise than cat owners and people without pets. The group without pets exhibited no statistically significant changes in health or behaviour. The results provide evidence that pet acquisition may have positive effects on human health and behaviour, and that for dog owners these effects are relatively long term.^[91] Pet ownership has also been associated with increased coronary artery disease survival, with dog owners being significantly less likely to die within one year of an acute myocardial infarction than those who did not own dogs.^[92]

Gunnar Kaasen and Balto, the lead dog on the last relay team of the 1925 serum run to Nome.

The health benefits of dogs can result from contact with dogs, not just from dog ownership. For example, when in the presence of a pet dog, people show reductions in cardiovascular, behavioral, and psychological indicators of anxiety.^[93] The benefits of contact with a dog also include social support, as dogs are able to not only provide companionship and social support themselves, but also to act as facilitators of social interactions between humans.^[94] One study indicated that wheelchair users experience more positive social interactions with strangers when they are accompanied by a dog than when they are not.^[95]

The practice of using dogs and other animals as a part of therapy dates back to the late 18th century, when animals were introduced into mental institutions to help socialize patients with mental disorders.^[96] Animal-assisted intervention research has shown that animal-assisted therapy with a dog can increase a person with Alzheimer’s disease’s social behaviours, such as smiling and laughing.^[97] One study demonstrated that children with ADHD and conduct disorders who participated in an education program with dogs and other animals showed increased attendance, increased knowledge and skill objectives, and decreased antisocial and violent behavior compared to those who were not in an animal-assisted program.^[98]

Shelters[link]

Every year, between 6 and 8 million dogs and cats enter US animal shelters.^[99] The Humane Society of the United States (HSUS) estimates that approximately 3 to 4 million dogs and cats are euthanized yearly in shelters across the United States.^[100] However, the percentage of dogs in US animal shelters that are eventually adopted and removed from the shelters by their new owners has increased since the mid 1990s from around 25% up to around 60–75% in the mid first decade of the 21st century.^[101]

Pets entering the shelters are euthanized in countries all over the world because of the lack of financial provisions to take care of these animals. Most shelters complain of not having enough resources to feed the pets and by being constrained to kill them, as the likelihood for all of them to find an owner is very small. In poor countries, euthanasia is usually violent.

Biology[link]

Lateral view of a dog's bone structure.

Domestic dogs have been selectively bred for millennia for various behaviors, sensory capabilities, and physical attributes.^[3] Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Nevertheless, their morphology is based on that of their wild ancestors, gray wolves.^[3] Dogs are predators and scavengers, and like many other predatory mammals, the dog has powerful muscles, fused wrist bones, a cardiovascular system that supports both sprinting and endurance, and teeth for catching and tearing.

Dogs are highly variable in height and weight. The smallest known adult dog was a Yorkshire Terrier, that stood only 6.3 centimetres (2.5 in) at the shoulder, 9.5 cm (3.7 in) in length along the head-and-body, and weighed only 113 grams (4.0 oz). The largest known dog was an English Mastiff which weighed 155.6 kilograms (343 lb) and was 250 cm (98 in) from the snout to the tail.^[102] The tallest dog is a Great Dane that stands 106.7 cm (42.0 in) at the shoulder.^[103]

Senses[link]

Vision[link]

Dog's visual colour perception compared with humans.

Like most mammals, dogs are dichromats and have color vision equivalent to red-green color blindness in humans (deuteranopia).^{[104][105][106][107]} Dogs are less sensitive to differences in grey shades than humans and also can detect brightness at about half the accuracy of humans.^[108]

The dog's visual system has evolved to aid proficient hunting.^[104] While a dog's visual acuity is poor (that of a poodle's has been estimated to translate to a Snellen rating of 20/75^[104]), their visual discrimination for moving objects is very high; dogs have been shown to be able to discriminate between humans (e.g., identifying their owner) at a range of between 800 and 900 m, however this range decreases to 500–600 m if the object is stationary.^[104]

Dogs have a temporal resolution of between 60 and 70 Hz, which explains why many dogs struggle to watch television, as most such modern screens are optimized for humans at 50–60 Hz.^[108] Dogs can detect a change in movement that exists in a single diopter of space within their eye. Humans, by comparison, require a change of between 10 and 20 diopters to detect movement.^[109][110]

The physiology of a dog ear.

As crepuscular hunters, dogs often rely on their vision in low light situations: They have very large pupils, a high density of rods in the fovea, an increased flicker rate, and a tapetum lucidum.^[104] The tapetum is a reflective surface behind the retina that reflects light to give the photoreceptors a second chance to catch the photons. There is also a relationship between body size and overall diameter of the eye. A range of 9.5 and 11.6 mm can be found between various breeds of dogs. This 20% variance can be substantial and is associated as an adaptation toward superior night vision.^[111]

The eyes of different breeds of dogs have different shapes, dimensions, and retina configurations.^[112] Many long-nosed breeds have a "visual streak" – a wide foveal region that runs across the width of the retina and gives them a very wide field of excellent vision. Some long-muzzled breeds, in particular, the sighthounds, have a field of vision up to 270° (compared to 180° for humans). Short-nosed breeds, on the other hand, have an "area centralis": a central patch with up to three times the density of nerve endings as the visual streak, giving them detailed sight much more like a human's. Some broad-headed breeds with short noses have a field of vision similar to that of humans.^[105][106]

Most breeds have good vision, but some show a genetic predisposition for myopia – such as Rottweilers, with which one out of every two has been found to be myopic.^[104] Dogs also have a greater divergence of the eye axis than humans, enabling them to rotate their pupils farther in any direction. The divergence of the eye axis of dogs ranges from 12–25° depending on the breed.^[109]

Experimentation has proven that dogs can distinguish between complex visual images such as that of a cube or a prism. Dogs also show attraction to static visual images such as the silhouette of a dog on a screen, their own reflections, or videos of dogs; however, their interest declines sharply once they are unable to make social contact with the image.^[113]

Hearing[link]

The frequency range of dog hearing is approximately 40 Hz to 60,000 Hz,^[114] which means that dogs can detect sounds far beyond the upper limit of the human auditory spectrum.^{[106][114][115]} In addition, dogs have ear mobility, which allows them to rapidly pinpoint the exact location of a sound.^[116] Eighteen or more muscles can tilt, rotate, raise, or lower a dog's ear. A dog can identify a sound's location much faster than a human can, as well as hear sounds at four times the distance.^[116]

Smell[link]

The wet, textured nose of a dog

While the human brain is dominated by a large visual cortex, the dog brain is dominated by an olfactory cortex.^[104] The olfactory bulb in dogs is roughly forty times bigger than the olfactory bulb in humans, relative to total brain size, with 125 to 220 million smell-sensitive receptors.^[104] The bloodhound exceeds this standard with nearly 300 million receptors.^[104]

Consequently, it has been estimated that dogs, in general, have an olfactory sense ranging from one hundred thousand to one million times more sensitive than a human's. In some dog breeds, such as bloodhounds, the olfactory sense may be up to 100 million times greater than a human's.^[117] The wet nose is essential for determining the direction of the air current containing the smell. Cold receptors in the skin are sensitive to the cooling of the skin by evaporation of the moisture by air currents.^[118]

Physical characteristics[link]

Coat[link]

A heavy winter coat with countershading in a mixed-breed dog

The coats of domestic dogs are of two varieties: "double" being common with dogs (as well as wolves) originating from colder climates, made up of a coarse guard hair and a soft down hair, or "single", with the topcoat only.

Domestic dogs often display the remnants of countershading, a common natural camouflage pattern. A countershaded animal will have dark coloring on its upper surfaces and light coloring below,^[119] which reduces its general visibility. Thus, many breeds will have an occasional "blaze", stripe, or "star" of white fur on their chest or underside.^[120]

Tail[link]

There are many different shapes for dog tails: straight, straight up, sickle, curled, or cork-screw. As with many canids, one of the primary functions of a dog's tail is to communicate their emotional state, which can be important in getting along with others. In some hunting dogs, however, the tail is traditionally docked to avoid injuries.^[121] In some breeds, puppies can be born with a short tail or no tail at all.^[122]

Types and breeds[link]

Cavalier King Charles Spaniels demonstrate with-breed variation.

While all dogs are genetically very similar,^[5] natural selection and selective breeding have reinforced certain characteristics in certain populations of dogs, giving rise to dog types and dog breeds. Dog types are broad categories based on function, genetics, or characteristics.^[123] Dog breeds are groups of animals that possess a set of inherited characteristics that distinguishes them from other animals within the same species. Modern dog breeds are non-scientific classifications of dogs kept by modern kennel clubs.

Purebred dogs of one breed are genetically distinguishable from purebred dogs of other breeds,^[43] but the means by which kennel clubs classify dogs is unsystematic. Systematic analyses of the dog genome has revealed only four major types of dogs that can be said to be statistically distinct.^[43] These include the "old world dogs" (e.g., Malamute and Shar Pei), "Mastiff"-type (e.g., English Mastiff), "herding"-type (e.g., Border Collie), and "all others" (also called "modern"- or "hunting"-type).^[43][124]

Health[link]

Dogs are susceptible to various diseases, ailments, and poisons, some of which can affect humans. To defend against many common diseases, dogs are often vaccinated.

A mixed-breed dog

Some breeds of dogs are prone to certain genetic ailments such as elbow or hip dysplasia, blindness, deafness, pulmonic stenosis, cleft palate, and trick knees. Two serious medical conditions particularly affecting dogs are pyometra, affecting unspayed females of all types and ages, and bloat, which affects the larger breeds or deep-chested dogs. Both of these are acute conditions, and can kill rapidly. Dogs are also susceptible to parasites such as fleas, ticks, and mites, as well as hookworm, tapeworm, roundworm, and heartworm.

Dogs are highly susceptible to theobromine poisoning, typically from ingestion of chocolate. Theobromine is toxic to dogs because, although the dog's metabolism is capable of breaking down the chemical, the process is so slow that even small amounts of chocolate can be fatal, especially dark chocolate.

Dogs are also vulnerable to some of the same health conditions as humans, including diabetes, dental and heart disease, epilepsy, cancer, hypothyroidism, and arthritis.^[125]

Mortality[link]

The typical lifespan of dogs varies widely among breeds, but for most the median longevity, the age at which half the dogs in a population have died and half are still alive, ranges from 10 to 13 years.^{[126][127][128][129]} Individual dogs may live well beyond the median of their breed.

The breed with the shortest lifespan (among breeds for which there is a questionnaire survey with a reasonable sample size) is the Dogue de Bordeaux, with a median longevity of about 5.2 years, but several breeds, including Miniature Bull Terriers, Bloodhounds, and Irish Wolfhounds are nearly as short-lived, with median longevities of 6 to 7 years.^[129]

The longest-lived breeds, including Toy Poodles, Japanese Spitz, Border Terriers, and Tibetan Spaniels, have median longevities of 14 to 15 years.^[129] The median longevity of mixed-breed dogs, taken as an average of all sizes, is one or more years longer than that of purebred dogs when all breeds are averaged.^{[127][128][129][130]} The dog widely reported to be the longest-lived is "Bluey," who died in 1939 and was claimed to be 29.5 years old at the time of his death; however, the Bluey record is anecdotal and unverified.^[131] On December 5, 2011, Pusuke, the world's oldest living dog recognized by Guinness Book of World Records, died aged 26 years and 9 months.^[132]

Predation[link]

Although wild dogs, like wolves, are apex predators, they can be killed in territory disputes with wild animals.^[133] Furthermore, in areas where both dogs and other large predators live, dogs can be a major food source for big cats or canines. Reports from Croatia indicate wolves kill dogs more frequently than they kill sheep. Wolves in Russia apparently limit feral dog populations. In Wisconsin, more compensation has been paid for dog losses than livestock.^[133] Some wolf pairs have been reported to prey on dogs by having one wolf lure the dog out into heavy brush where the second animal waits in ambush.^[134] In some instances, wolves have displayed an uncharacteristic fearlessness of humans and buildings when attacking dogs, to the extent that they^[which?] have to be beaten off or killed.^[135]

Coyotes and big cats have also been known to attack dogs. Leopards in particular are known to have a predilection for dogs, and have been recorded to kill and consume them regardless of the dog's size or ferocity.^[136] Tigers in Manchuria, Indochina, Indonesia, and Malaysia are reputed to kill dogs with the same vigor as leopards.^[137] Striped Hyenas are major predators of village dogs in Turkmenistan, India, and the Caucasus.^[138] Reptiles such as alligators and pythons have been known to kill and eat dogs.