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Meat

Meat

Meat is animal tissue (mainly muscle) used as food. The common definition of meat is dependent on culture. Many Americans would exclude organ meat, fish, and other seafood from their definition of meat. Originally, the word meat meant simply "food." It is also used as a vulgar way to refer to the human body (see meat market). meat market For the most part, meat for human consumption comes from domesticated animals bred specifically for this purpose, and killed in an abattoir. The use of other meats, such as venison, the meat of small game animals and a few other mammals, and even the meat of certain reptiles and amphibians, is not uncommon. The meat of a large array of other mammal species is eaten in some countries. What meats are used and the way they are cooked depends on the availability and cuisine. Thin sliced meats used in sandwich-making are called cold cuts in the United States. In recent years, forms of imitation meat have been created to satisfy some vegetarians' taste for the flavour and texture of meat, and there is speculation about the possibility of growing in vitro meat from animal tissue. __FORCETOC__

Taboo meat

Main article: Taboo food and drink Some types of meat (such as pork or beef) are taboo for certain religions while others are taboo due to their association as pets in those countries, with the notable exception of rabbits in the West. Judaism labels the meat of some animals, if slaughtered properly, as kosher, or "fit", and the rest are considered not kosher, or "unfit" (also called treif, literally, "torn"). In Islam, permitted meats are termed halal. Until the mid-1960s, the Catholic Church forbade the eating of meat on Fridays. American Catholics are only asked not to eat meat on Ash Wednesday, Good Friday and Fridays during Lent. Mahayana Buddhist belief forbids the killing of animals because of the bad karma believed to be generated. However Theravadin Buddhists may eat meat if it can be determined that the animal was not slaughtered specifically for their consumption. In Hinduism, which shares the Buddhist concept of karma, cattle are regarded as specially sacred, and even those Hindus who eat meat generally refrain from eating beef. Most Hindus regard killing of animals as a violation of the concept of ahimsa. It is estimated that approximately 30% of all Hindus are vegetarians. Jainism has vegetarianism as one of its central dogmas. Human meat is considered taboo in most cultures due to concerns of both murder and disease transmission; the term "cannibal" is a pejorative in those cultures.

List of meats

The following list of meats includes animals which some cultures never eat or do not consider meat, as well as endangered species.
- amphibians
- frog
- salamander
- toad
- artificial meat
- imitation meat
- in vitro meat
- beef (bovines)
- American Bison
- cattle
- steak
- veal (calves)
- yak
- poultry (birds)
- chicken
- duck
- game birds
- dove
- New World quail
- pheasant
- grouse
- partridge
- quail
- pigeon
- woodcock
- goose
- turkey
- canids
- dog
- fox
- wolf
- felines
- cat
- lion
- tiger
- seafood
- fish
- shark
- cephalopods
- cuttlefish
- octopus
- squid
- crustaceans
- crab
- crayfish
- lobster
- prawn
- shrimp
- shellfish (mollusks)
- abalone
- clam
- mussel
- oyster
- scallop
- snail
- cetaceans
- whale
- dolphin
- equines
- horses
- zebras
- lagomorphs
- hare
- pika
- rabbit
- marsupials
- kangaroo
- opossum
- wallabee
- mutton (sheep)
- lamb
- pork (pigs)
- ham (haunch)
- bacon (cured strips of meat)
- primates
- gorilla
- orangutan
- chimpanzee
- bonobo
- human (cannibalism)
- monkey
- reptiles
- turtle
- lizard
- snake
- iguana
- crocodile
- alligator
- rodents
- beaver
- guinea pig
- muskrat
- rat
- squirrel
- venison (antlered animals)
- caribou (reindeer)
- deer
- elk
- moose
- antelopes
- giraffe
- weasels
- insects
- grasshoppers
- ants
- bees
- cockroaches
- beetles
- larvae
- grubs
- caterpillars
- others
- elephant
- rhinoceros
- bear

Animal

:For the Muppet Show character, see Animal (Muppet). For the professional wrestler, see Joseph Laurinaitis.

- Porifera (sponges)
- Ctenophora (comb jellies)
- Cnidaria (coral, jellyfish, anenomes)
- Placozoa (trichoplax)
- Subregnum Bilateria (bilateral symmetry)
- Acoelomorpha (basal)
- Orthonectida (flatworms, echinoderms, etc.)
- Rhombozoa (dicyemids)
- Myxozoa (slime animals)
- Superphylum Deuterostomia (blastopore becomes anus)
- Chordata (vertebrates, etc.)
- Hemichordata (acorn worms)
- Echinodermata (starfish, urchins)
- Chaetognatha (arrow worms)
- Superphylum Ecdysozoa (shed exoskeleton)
- Kinorhyncha (mud dragons)
- Loricifera
- Priapulida (priapulid worms)
- Nematoda (roundworms)
- Nematomorpha (horsehair worms)
- Onychophora (velvet worms)
- Tardigrada (water bears)
- Arthropoda (insects, etc.)
- Superphylum Platyzoa
- Platyhelminthes (flatworms)
- Gastrotricha (gastrotrichs)
- Rotifera (rotifers)
- Acanthocephala (acanthocephalans)
- Gnathostomulida (jaw worms)
- Micrognathozoa (limnognathia)
- Cycliophora (pandora)
- Superphylum Lophotrochozoa (trochophore larvae / lophophores)
- Sipuncula (peanut worms)
- Nemertea (ribbon worms)
- Phoronida (horseshoe worms)
- Ectoprocta (moss animals)
- Entoprocta (goblet worms)
- Brachiopoda (brachipods)
- Mollusca (mollusks)
- Annelida (segmented worms) Animals are a major group of organisms, classified as the kingdom Animalia or Metazoa. In general they are multicellular, capable of locomotion and responsive to their environment, and feed by consuming other organisms. Their body plan becomes fixed as they develop, usually early on in their development as embryos, although some undergo a process of metamorphosis later on. Along with sponges, gastropods, emus, dolphins and all other animals, Homo sapiens sapiens meet all the criteria above for membership in the group of organisms known as animals and they do not meet the criteria of the other groups. Some humans often consider themselves separate from animals, not on the grounds of biology, but through the use of "other contexts". Whilst self-delusion may be a unique characteristic of the human species it is not cause for exclusion from the Kingdom Animalia. The name animal comes from the Latin word animal, of which animalia is the plural, and ultimately from anima, meaning vital breath or soul.

Characteristics

Aristotle divided the living world between animals and plants, and this was followed by Carolus Linnaeus in the first hierarchical classification. Since then biologists have begun emphasizing evolutionary relationships, and so these groups have been restricted somewhat. For instance, microscopic protozoa were originally considered animals because they move, but are now treated separately. Kingdom Animalia has several characteristics that set it apart from other living things. First, animals are eukaryotic. This separates them from the Kingdom Monera. Second, animals are multicellular, which separates them from Kingdom Protista. Third, they are heterotrophic, setting them apart from Kingdom Plantae and several plant-like protists. Finally, Kingdom Animalia consists of organisms without cell walls, which makes it unique compared to Kingdom Plantae, algae, and Kingdom Fungi.

Structure

With a few exceptions, most notably the sponges (Phylum Porifera), animals have bodies differentiated into separate tissues. These include muscles, which are able to contract and control locomotion, and a nervous system, which sends and processes signals. There is also typically an internal digestive chamber, with one or two openings. Animals with this sort of organization are called metazoans, or eumetazoans when the former is used for animals in general. All animals have eukaryotic cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells, bones, and spicules. During development it forms a relatively flexible framework upon which cells can move about and be reorganized, making complex structures possible. In contrast, other multicellular organisms like plants and fungi have cells held in place by cell walls, so develop by progressive growth. Also, unique to animal cells are the following intercellular junctions: tight junctions, gap junctions, and desmosomes.

Reproduction and development

Nearly all animals undergo some form of sexual reproduction. Adults are diploid or occasionally polyploid. They have a few specialized reproductive cells, which undergo meiosis to produce smaller motile spermatozoa or larger non-motile ova. These fuse to form zygotes, which develop into new individuals. Many animals are also capable of asexual reproduction. This may take place through parthenogenesis, where fertile eggs are produced without mating, or in some cases through fragmentation. A zygote initially develops into a hollow sphere, called a blastula, which undergoes rearrangement and differentiation. In sponges, blastula larvae swim to a new location and develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement. It first invaginates to form a gastrula with a digestive chamber, and two separate germ layers - an external ectoderm and an internal endoderm. In most cases, a mesoderm also develops between them. These germ layers then differentiate to form tissues and organs. Animals grow by indirectly using the energy of sunlight. Plants use this energy to turn air into simple sugars using a process known as photosynthesis. These sugars are then used as the building blocks which allow the plant to grow. When animals eat these plants (or eat other animals which have eaten plants), the sugars produced by the plant are used by the animal. They are either used directly to help the animal grow, or broken down, releasing stored solar energy, and giving the animal the energy required for motion. This process is known as glycolysis.

Origin and fossil record

Animals are generally considered to have evolved from flagellate protozoa. Their closest living relatives are the choanoflagellates, collared flagellates that have the same structure as certain sponge cells do. Molecular studies place them in a supergroup called the opisthokonts, which also include the fungi and a few small parasitic protists. The name comes from the posterior location of the flagellum in motile cells, such as most animal sperm, whereas other eukaryotes tend to have anterior flagella. The first fossils that might represent animals appear towards the end of the Precambrian, around 600 million years ago, and are known as the Vendian biota. These are difficult to relate to later fossils, however. Some may represent precursors of modern phyla, but they may be separate groups, and it is possible they are not really animals at all. Aside from them, most animal phyla with known phyla make a more or less simultaneous appearance during the Cambrian period, about 570 million years ago. It is still disputed whether this event, called the Cambrian explosion, represents a rapid divergence between different groups or a change in conditions that made fossilization possible.

Groups of animals

The sponges (Porifera) diverged from other animals early. As mentioned, they lack the complex organization found in most other phyla. Their cells are differentiated, but not organized into distinct tissues. Sponges are sessile and typically feed by drawing in water through pores all over the body, which is supported by a skeleton typically divided into spicules. The extinct Archaeocyatha, which have fused skeletons, may represent sponges or a separate phylum. Among the eumetazoan phyla, two are radially symmetric and have digestive chambers with a single opening, which serves as both the mouth and the anus. These are the Cnidaria, which include anemones, corals, and jellyfish, and the Ctenophora or comb jellies. Both have distinct tissues, but they are not organized into organs. There are only two main germ layers, the ectoderm and endoderm, with only scattered cells between them. As such, these animals are sometimes called diploblastic. The tiny phylum Placozoa is similar, but individuals do not have a permanent digestive chamber. The remaining animals form a monophyletic group called the Bilateria. For the most part, they are bilaterally symmetric, and often have a specialized head with feeding and sensory organs. The body is triploblastic, i.e. all three germ layers are well-developed, and tissues form distinct organs. The digestive chamber has two openings, a mouth and an anus, and there is also an internal body cavity called a coelom or pseudocoelom. There are exceptions to each of these characteristics, however - for instance adult echinoderms are radially symmetric, and certain parasitic worms have extremely simplified body structures. Genetic studies have considerably changed our understanding of the relationships within the Bilateria. Most appear to belong to four major lineages: # Deuterostomes # Ecdysozoa # Platyzoa # Lophotrochozoa In addition to these, there are a few small groups of bilaterians with relatively similar structure that appear to have diverged before these major groups. These include the Acoelomorpha, Rhombozoa, and Orthonectida. The Myxozoa, single-celled parasites that were originally considered Protozoa, are now believed to have developed from the Bilateria as well.

Deuterostomes

Deuterostomes differ from the other Bilateria, called protostomes, in several ways. In both cases there is a complete digestive tract. However, in protostomes the initial opening (the archenteron) develops into the mouth, and an anus forms separately. In deuterostomes this is reversed. In most protostomes cells simply fill in the interior of the gastrula to form the mesoderm, called schizocoelous development, but in deuterostomes it forms through evagination of the endoderm, called enterocoelic pouching. Deuterostomes also have a dorsal, rather than a ventral, nerve chord and their embryos undergo different cleavage. All this suggests the deuterostomes and protostomes are separate, monophyletic lineages. The main phyla of deuterostomes are the Echinodermata and Chordata. The former are radially symmetric and exclusively marine, such as sea stars, sea urchins, and sea cucumbers. The latter are dominated by the vertebrates, animals with backbones. These include fish, amphibians, reptiles, birds, and mammals. In addition to these, the deuterostomes also include the Hemichordata or acorn worms. Although they are not especially prominent today, the important fossil graptolites may belong to this group. The Chaetognatha or arrow worms may also be deuterostomes, but this is less certain.

Ecdysozoa

The Ecdysozoa are protostomes, named after the common trait of growth by moulting or ecdysis. The largest animal phylum belongs here, the Arthropoda, including insects, spiders, crabs, and their kin. All these organisms have a body divided into repeating segments, typically with paired appendages. Two smaller phyla, the Onychophora and Tardigrada, are close relatives of the arthropods and share these traits. The ecdysozoans also include the Nematoda or roundworms, the second largest animal phylum. Roundworms are typically microscopic, and occur in nearly every environment where there is water. A number are important parasites. Smaller phyla related to them are the Nematomorpha or horsehair worms, which are visible to the unaided eye, and the Kinorhyncha, Priapulida, and Loricifera, which are all microscopic. These groups have a reduced coelom, called a pseudocoelom. The remaining two groups of protostomes are sometimes grouped together as the Spiralia, since in both embryos develop with spiral cleavage.

Platyzoa

The Platyzoa include the phylum Platyhelminthes, the flatworms. These were originally considered some of the most primitive Bilateria, but it now appears they developed from more complex ancestors. A number of parasites are included in this group, such as the flukes and tapeworms. Flatworms lack a coelom, as do their closest relatives, the microscopic Gastrotricha. The other platyzoan phyla are microscopic and pseudocoelomate. The most prominent are the Rotifera or rotifers, which are common in aqueous environments. They also include the Acanthocephala or spiny-headed worms, the Gnathostomulida, Micrognathozoa, and possibly the Cycliophora. These groups share the presence of complex jaws, from which they are called the Gnathifera.

Lophotrochozoa

The Lophotrochozoa include two of the most successful animal phyla, the Mollusca and Annelida. The former includes animals such as snails, clams, and squids, and the latter comprises the segmented worms, such as earthworms and leeches. These two groups have long been considered close relatives because of the common presence of trochophore larvae, but the annelids were considered closer to the arthropods, because they are both segmented. Now this is generally considered convergent evolution, owing to many morphological and genetic differences between the two phyla. The Lophotrochozoa also include the Nemertea or ribbon worms, the Sipuncula, and several phyla that have a fan of cilia around the mouth, called a lophophore. These were traditionally grouped together as the lophophorates, but it now appears they are paraphyletic, some closer to the Nemertea and some to the Mollusca and Annelida. They include the Brachiopoda or lamp shells, which are prominent in the fossil record, the Entoprocta, the Phoronida, and possibly the Ectoprocta or moss animals.

History of classification

In Linnaeus' original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, the Chordata, whereas the various other forms have been separated out. The above lists represent our current understanding of the group, though there is some variation from source to source.

Usage of the word animal

In everyday usage animal refers to any member of the animal kingdom that is not a human being, and sometimes excludes insects (although including such arthropods as crabs). This confusion stems primarily from the familiarity with zoo animals, farm animals and pets, not from an analytical distinction between insects, humans and the rest of the animal kingdom.

Examples

Some well-known types of animals, listed by their common names:
- alpaca, ant, antelope, badger, bat, bear, bee, beetle, bird, bison, butterfly, cat, chicken, cockroach, coral, cow, deer, dinosaur, dog, dolphin, earthworm, elephant, elk, fish, fly, fox, frog, giraffe, goat, gorilla, hippopotamus, horse, human, iguana, jellyfish, kangaroo, lion, lizard, llama, lynx, monkey, mouse, nightingale, octopus, owl, ox, parrot, penguin, pig, quail, rabbit, rat, rhinoceros, salamander, scorpion, seahorse, shark, sheep, sloth, snake, spider, squid, starfish, tiger, turtle, urial, vole, whale, wolf, yak, zebra

References

External links

- [http://www.animool.com/animals/index.jsp Animals Search Engine]
- [http://www.wikianimals.com wikianimals.com] - Documenting the animal kingdom
- [http://tolweb.org/tree?group=Animals&contgroup=Eukaryotes Tree of Life]
- [http://www.arkive.org A Multimedia Database of Various UK or Endangered Species]
- [http://freepages.genealogy.rootsweb.com/~wakefield/animals.html Animals and Birds Names] - Large table of words: animal, collective, male, female, young, & home
- [http://www273.pair.com/med/words/animal_adjectives.htm English Animal Adjectives]
- [http://www.georgetown.edu/faculty/ballc/animals/animals.html Sounds of the World's Animals] - animal sounds in many languages
- [http://www.findsounds.com/ FindSounds - Search the Web for Sounds] - sound files including animal sound files
- [http://www.australianfauna.com/ Australian Animals]
- [http://www.animalreviews.com AnimalReviews] - animals reviewed and evaluated
- [http://animals.timduru.org/ The animal photo archive] - Photos of animals
- [http://www.wildlife-photo.org Photo gallery of animals pictures from the entire world.]
- [http://www.wildlife-photo.org/birds_list.htm Birds Name Check List in Latin, English, Russian and Hebrew.]
- [http://www.wildanimalsonline.com Wild Animals Online] - an online encyclopedia of wild animals - facts, photos Category:Animals zh-min-nan:Tōng-bu̍t ko:동물 ms:Haiwan ja:動物 simple:Animal th:สัตว์

Muscle

Muscle is a contractile form of tissue. It is one of the four major tissue types, the other three being epithelium, connective tissue and nervous tissue. Muscle contraction is used to move parts of the body, as well as to move substances within the body.

Types

There are three general types of muscle:
- Cardiac muscle is a specalized kind of muscle found only within the heart.
- Skeletal muscle or "voluntary muscle" is anchored by tendons to bone and is used to effect skeletal movement such as locomotion.
- Smooth muscle or "involuntary muscle" is found within structures such as the intestines, throat and blood vessels. Cardiac and skeletal muscle are "striated" in that they contain sarcomeres and are packed into highly regular arrangements of bundles; smooth muscle has neither. Striated muscle is often used in short, intense bursts, whereas smooth muscle sustains longer or even near-permanent contractions. Skeletal muscle is further divided into two subtypes:
- Type I, slow oxidative, slow twitch, or "red" muscle is dense with capillaries and is rich in mitochondria and myoglobin, giving the muscle tissue its characteristic red color. It can carry more oxygen and sustain aerobic activity.
- Type II, glycolytic, fast twitch, or "white" muscle is less dense in mitochondria and myoglobin. It can contract more quickly and with a greater amount of force than Type I muscle, but can sustain only short, anaerobic bursts of activity before a build-up of lactic acid in tissue begins to interfere with muscular contraction and causes pain.

Anatomy

Muscle is composed of muscle cells (sometimes known as "muscle fibers"). Within the cells are myofibrils; myofibrils contain sarcomeres, which are composed of actin and myosin. Individual muscle cells are lined with endomysium. Muscle cells are bound together by perimysium into bundles called fascicles; the bundles are then grouped together to form muscle, which is lined by epimysium. Muscle spindles are distributed throughout the muscles and provide feedback sensory information to the central nervous system. Skeletal muscle is arranged in discrete groups, examples of which include the biceps brachii. It is connected by tendons to processes of the skeleton. In contrast, smooth muscle occurs at various scales in almost every organ, from the skin (in which it controls erection of body hair) to the blood vessels and digestive tract (in which it controls the caliber of a lumen and peristalsis).

Physiology

The three types of muscle have significant differences, but all use the movement of actin against myosin to produce contraction and relaxation. In skeletal muscle, contraction is stimulated by electrical impulses transmitted by the nerves, the motor nerves and motoneurons in particular. All skeletal muscle and many smooth muscle contractions are facilitated by the neurotransmitter acetylcholine. Muscles and muscular activity account for most of the body's energy consumption. Muscles store energy for their own use in the form of glycogen, which represents about 1% of their mass. This can be rapidly converted to glucose when more energy is necessary.

Nervous control

Efferent leg

Vertebrates move muscles in response to voluntary and autonomic signals from the brain. Deep muscles, superficial muscles, muscles of the face and internal muscles all correspond with dedicated regions in the brain. In addition, muscles react to reflexive nerve stimuli that do not always send signals all the way to the brain, but most muscle activity is the result of complex interactions between various areas of the brain. Nerves that control skeletal muscles in mammals correspond with neuron groups along the primary motor cortex of the brain's cerebral cortex. Commands are routed though the basal ganglia and are modified by input from the cerebellum before being relayed through the pyramidal tract to the spinal cord and from there to the motor end plate at the muscles. Along the way, feedback loops such as that of the extrapyramidal system contribute signals to influence muscle tone and response. Deeper muscles such as those involved in posture often are controlled from nuclei in the brain stem and basal ganglia.

Afferent leg

Sometimes known as muscle memory, the sense of where our bodies are in space is called proprioception, the perception of body awareness. More easily demonstrated than explained, proprioception is the "unconscious" awareness of where the various regions of the body are located at any one time. This can be demonstrated by anyone closing their eyes and waving their hand around. Assuming proper proprioceptive function, at no time will the person lose awareness of where the hand actually is, even though it is not being detected by any of the other senses. Several areas in the brain coordinate movement and position with the feedback information gained from proprioception. The cerebellum and nucleus ruber in particular continuously sample position against movement and make minor corrections to assure a smooth projection.

Role in health and disease

Exercise

Exercise is often recommended as a means of improving motor skills, fitness and muscle strength. Exercise has several effects upon muscles, connective tissue and bone, and the nerves that stimulate the muscles.

Disease

Symptoms of muscle disease may include weakness or spasticity/rigidity, myoclonus (twitching) and myalgia (muscle pain). Diagnostic procedures that may reveal muscular disorders include testing creatine kinase levels in the blood and electromyography (measuring electrical activity in muscles). Neuromuscular diseases are those that affect the muscles and/or their nervous control. In general, problems with nervous control can cause spasticity or paralysis, depending on the location and nature of the problem. A large proportion of neurological disorders leads to problems with movement, ranging from cerebrovascular accident (stroke) and Parkinson's disease to Creutzfeldt-Jakob disease. Diseases of the motor end plate include myasthenia gravis, a form of muscle weakness due to antibodies to the acetylcholine receptor, and its related condition Lambert-Eaton myasthenic syndrome (LEMS). Tetanus and botulism are bacterial infections in which bacterial toxins cause increased or decreased muscle tone, respectively. The myopathies are all diseases affecting the muscle itself, rather than its nervous control. Muscular dystrophy is a large group of diseases, many of them hereditary, where the muscle integrity is disrupted. It leads to progressive loss of strength, high dependence and decreased life span. Inflammatory muscle disorders:
- Polymyalgia rheumatica (or "muscle rheumatism") is an inflammatory condition that mainly occurs in the elderly; it is associated with giant-cell arteritis. It often responds dramatically to glucocorticoids (e.g. prednisolone).
- Polymyositis, dermatomyositis and inclusion body myositis are autoimmune conditions in which the muscle is affected. Rhabdomyolysis is the breakdown of muscular tissue due to any cause. While it may not lead to any muscular symptoms at all, the myoglobin thus released may cause acute renal failure. Tumors of muscle include:
- Smooth muscle: leiomyoma (benign, very common in the uterus), leiomyosarcoma (malignant, very rare)
- Striated muscle: rhabdomyoma (benign) and rhabdomyosarcoma (malignant) - both very rare
- Metastasis from elsewhere (e.g. lung cancer) Smooth muscle has been implicated to play a role in a large number of diseases affecting blood vessels, the respiratory tract (e.g. asthma), the digestive system (e.g. irritable bowel syndrome) and the urinary tract (e.g. urinary incontinence). These disease processes are not usually confined to the muscular tissue.

The strongest human muscle

Depending on what definition of "strongest" is used, many different muscles in the human body can be characterized as being the "strongest." In ordinary parlance, muscular "strength" usually refers to the ability to exert a force on an external object—for example, lifting a weight. By this definition, the masseter or jaw muscle is the strongest. The 1992 Guinness Book of Records records the achievement of a bite strength of 975 lbf (4337 N) for two seconds. What distinguishes the masseter is not anything special about the muscle itself, but its advantage in working against a much shorter lever arm than other muscles. If "strength" refers to the force exerted by the muscle itself, e.g. on the place where it inserts into a bone, then the strongest muscles are those with the largest cross-sectional area at their belly. This is because the tension exerted by an individual skeletal (striated) muscle fiber does not vary much, either from muscle to muscle, or with length. Each fiber can exert a force on the order of 0.3 micronewtons. By this definition, the strongest muscle of the body is usually said to be the Quadriceps femoris or the Gluteus maximus. Again taking strength to mean only "force" (in the physicist's sense, and as contrasted with "energy" or "power"), then a shorter muscle will be stronger "pound for pound" (i.e. by weight) than a longer muscle. The uterus may be the strongest muscle by weight in the human body. At the time when an infant is delivered, the human uterus weighs about 40 oz (1.1 kg). During childbirth, the uterus exerts 25 to 100 lbf (100 to 400 N) of downward force with each contraction. The external muscles of the eye are conspicuously large and strong in relation to the small size and weight of the eyeball. It is frequently said that they are "the strongest muscles for the job they have to do" and are sometimes claimed to be "100 times stronger than they need to be." Eye movements, however, are and probably "need" to be exceptionally fast. The unexplained statement that "the tongue is the strongest muscle in the body" appears frequently in lists of surprising facts, but it is difficult to find any definition of "strength" that would make this statement true. Note that technically the tongue consists of sixteen muscles, not one. The tongue may possibly be the strongest muscle at birth. The heart has a claim to being the muscle that performs the largest quantity of physical work in the course of a lifetime. Estimates of the power output of the human heart range from 1 to 5 watts. This is much less than the maximum power output of other muscles; for example, the quadriceps can produce over 100 watts, but only for a few minutes. The heart does its work continuously over an entire lifetime without pause, and thus can "outwork" other muscles. An output of one watt continuously for seventy years yields a total work output of 2 to 3 ×10⁹ joules.

Efficiency

The efficiency of human muscle has been measured (in the context of rowing and cycling) at 14% to 27%. The efficiency is defined as the ratio of mechanical work done to the total energy output (heat plus work).

Muscle evolution

According to a recent study published in 1999 [http://www.umbi.umd.edu/~collins/myoinformatics/muscle-evolution.pdf], specialized forms of skeletal and cardiac muscles predated the divergence of the vertebrate/arthropod evolutionary line. This indicates that these types of muscle developed in a common ancestor sometime before 700 million years ago (mya). Vertebrate smooth muscle (smooth muscle found in humans) was found to have evolved independently from the skeletal and cardiac muscles.

References

- Costill, Jack H. and Wilmore, David L. (2004). Physiology of Sport and Exercise. Champaign, Illinois: Human Kinetics. ISBN 0736044892.
- Phylogenetic Relationship of Muscle Tissues Deduced from Superimposition of Gene Trees, Satoshi OOta and Naruya Saitou, Mol. Biol. Evol. 16(6) 856-7, 1999

External links

- [http://www.straightdope.com/mailbag/mmuscle.html The Straight Dope] (Masseter "strongest;" 975 pounds for 2 seconds; gluteus maximus and quadriceps strongest if leverage not included)
- [http://hypertextbook.com/facts/2003/IradaMuslumova.shtml Physics factbook] (Heart output 1.3 to 5 watts, lifetime output 2 to 3 ×10⁹ joules)
- [http://www.akoa.org/story.dbm?sid=167 Alaska optometric association] (External eye muscles "100 times as strong as they need to be")
- [http://www.courses.vcu.edu/DANC291-003/unit_7.htm course notes for a Virginia Commonwealth dance course] (Quadriceps "strongest")
- [http://www.ergo-fit.de/english/scripts/produkteneu/produktgruppe.php?gruppe=17&hgruppe=7&familie=1 a body-building equipment website] (Quadriceps "strongest")
- [http://www.dundee.ac.uk/medther/StrokeSSM/ClinExamNeuro.htm University of Dundee] article on performing neurological examinations (Quadriceps "strongest")
- [http://www.hartnell.cc.ca.us/faculty/asteinhardt/development.htm course notes from a Hartnell College course] (Uterus "strongest pound for pound")
- [http://pregnancytoday.com/resource/definitions/uterus.htm the Pregnancy Today website] (Uterus "strongest")
- [http://www.coachesinfo.com/category/rowing/77/ Muscle efficiency in rowing]
- [http://www.gssiweb.com/reflib/attachment.cfm?id=11 "Gatorade Sports Science Institute" on muscle efficiency in cyclists (PDF)]

Food

Food is any substance that can be consumed, including liquid drinks. Food is the main source of energy and of nutrition for animals, and is usually of animal or plant origin. The study of food is called food science. In English, the term food is often used metaphorically or figuratively, as in food for thought. Food can also be a system of communication, a collection of images, a protocol of usages, situations, and behavior. Food is what brings the memory of our past into our contemporary life.

Legal definition

Western food law defines four categories of object as food:
- any substance or product, whether processed, partially processed or unprocessed, intended to be, or reasonably expected to be ingested by humans whether of nutritional value or not;
- water and other drinks;
- chewing gum;
- articles and substances used as an ingredient or component in the preparation of food. Links to official legal definitions of food:
- [http://www.fda.gov/opacom/laws/fdcact/fdcact1.htm US federal definition of food]
- [http://www.legislation.hmso.gov.uk/acts/acts1990/Ukpga_19900016_en_2.htm#mdiv1 UK definition of food]
- [http://europa.eu.int/smartapi/cgi/sga_doc?smartapi!celexapi!prod!CELEXnumdoc&lg=EN&numdoc=32002R0178&model=guichett EU definition of food]

Human eating habits

Historical development

Humans are commonly believed to be omnivorous animals that can consume both plant and animal products. Evidence suggests that early Homo Sapiens employed Hunter-gatherer as their primary means of food collection. This involves combining stationary plant and fungal food sources (such as fruits, grains, roots, and mushrooms) with mobile animals which must be hunted and killed in order to be consumed. Additionally, it is believed that humans have used fire to prepare food prior to eating since their divergence from Homo erectus, possibly even earlier. At least ten thousand years ago, humans developed agriculture, which has Timeline of agriculture and food and altered the kind of food people eat. This has led to a variety of important historical consequences, such as increased [[population]], the development of [[cities, and the wider spread of infectious diseases. The types of food consumed, and the way in which they are prepared has varied widely by time, location, and culture.

Meals

A portion of food or the act of eating a portion of food is considered a meal. Often named and patterned, meals play a role in an important social occasion, such as the celebration of many key cultural and religious festivals. A meal can be used as means for feeding a single individual or shared and eaten simultaneously by two or more people. The number of meals consumed by individuals in a day, their size, composition, when and how they are prepared and eaten varies greatly around the world. This diversity can be attributed to a number of local factors, including climate, ecology, economy, cultural traditions and industrialisation. In societies where the availability of food has risen above subsistence levels and beyond staple foods, meals are also sold pre-prepared for immediate consumption in restaurants and other similar retail premises. Food eaten in smaller quantities between the culturally normative meals is regarded as snack food. :See also: Appetite, Buddhist cuisine, Eucharist, Fast food, Fasting, Gault Millau restaurant guide, Halaal, I-tal, Kashrut, Michelin restaurant guide, Muslim dietary laws, Potluck, Totemism.

Food production or acquisition

Food is traditionally obtained through farming, ranching, and fishing, with hunting, foraging and other methods of subsistence locally important for some populations, but minor for others. In the modern era in developed nations, food supply is increasingly dependent upon agriculture, industrial farming, aquaculture and fish farming techniques. These techniques aim to maximize the amount of food produced while minimizing the cost. The techniques include a reliance on mechanized tools, from the threshing machine and seed drill, to the tractor and combine. Developed tools have been combined with the use of pesticides to promote high crop yields and to combat insects or mammals which reduce yield. More recently, there has been a growing trend towards more Sustainable agricultural practices. This approach - which is partly fuelled by consumer demand - encourages biodiversity, local self-reliance and Organic farming methods. Major influences on food production are international policy, e.g. the World Trade Organization and Common Agricultural Policy, national government policy or law and war. Food for livestock is fodder and traditionally comprises hay or grain. :See also: mariculture, horticulture, agribusiness, gardening. gardening

From plants

- Seeds
- Cereals from grasses, including barley, maize, oats, rice, rye, and wheat
- Cereals from non-grasses, including buckwheat, amaranth, and quinoa
- Legumes, including beans, peas, and lentils
- Nuts, including coconuts, almonds, and pine nuts
- Oilseeds, including sesame, sunflower, and hemp
- Vegetables (see also list of vegetables)
- Root vegetables, including potatoes, cassava, and turnips
- Leaf vegetables, including amaranth, spinach, and kale
- Sea vegetables, including dulse, kombu, and dabberlocks
- Stem vegetables, including bamboo shoots, nopales, and asparagus
- inflorescence vegetables, including globe artichokes, broccoli, and daylilies
- Fruit vegetables, including pumpkin, okra, and eggplant
- Fruits (see also list of fruits)
- Herbs and spices (see also list of herbs and spices) list of herbs and spices

From animals

- Dairy products, including milk
- Eggs, including roe and caviar
- Insects, including honey
- Meat, including beef, frogs' legs, goat, horse, kangaroo, lamb, mutton, pork, veal, rodents, human (i.e. cannibalism)
- Offal, including blood
- Poultry, including chicken, turkey, duck, goose, pigeon or dove, ostrich, emu, guinea fowl, pheasant, quail
- Seafood, including finfish such as salmon and tilapia, and shellfish such as mollusks and crustaceans
- Snails
- Game, this includes all animals hunted for food.

From neither animals or plants

- Salt
- Mushrooms, which are a type of fungi
- Seaweed, which is a protist
- Water, including mineral water and spring (water)

Food preparation

spring (water) While some food can be eaten without preparation, many foods undergo some form of preparation for reasons of safety, palatability, or flavor. At the simplest level this may involve washing, cutting, trimming or adding other foods or ingredients, such as spices. It may also involve mixing, heating or cooling, pressure cooking, fermentation, or combination with other food. Most food preparation takes place in a kitchen. The preparation of animal-based food will usually involve slaughter, evisceration, hanging, portioning and rendering. :See also: Barbecue, Eating utensils, Frankfurt kitchen, Hangi, Oven, Microwave oven, Refrigeration, Food preparation utensils.

Food manufacture

Early food processing techniques were limited by the available food preservation, packaging and transportation. Early food processing mainly involved salting, curing, curdling, drying, pickling and smoking. An early processed food product was cheese. During the industrialisation era in the 19th century, food manufacturing arose. This development took advantage of new mass markets and emerging new technology, such as milling, preservation, packaging and labelling and transportation. It brought the advantages of pre-prepared time saving food to the bulk of ordinary people who did not employ domestic servants. At the start of the 21st century, a two-tier structure has arisen, with a few international food processing giants controlling a wide range of well known food brands; with a populous number of small local or national food processing companies. :See also: Best before, Canning, Coloring, Food quality, Snap freezing, Additives, Flavoring, Enzymes, Genetically modified food, Pasteurization, Shelf-life, Ultra-high temperature processing.

Types of manufactured food

- Drinks: beer, juice, soft drink, squash, wine.
- Bread is a staple food for many nations, being made of risen dough of wheat or other cereals.
- Cakes and cookies
- Cheese is a curdled milk product, of which many varieties exist.
- Dessert is a course, usually sweet, and generally served after the main course, e.g. Ice cream.
- French fries, Chips
- Functional food
- Jam and Jelly
- Pasta
- Pie
- Pizza
- Processed meats
- Sandwiches
- Salad
- Sauce
- Sausage

Food trade

Food is now traded on a global basis. The variety and availability of food is no longer restricted by the diversity of locally grown food or the limitations of the local growing season. Between 1961 and 1999 there has been a 400% increase in worldwide food exports. Some countries are now economically dependent on food exports, which in some cases account for over 80% of all exports. In 1994 trade liberalisation began when over 100 countries became signatories to the Uruguay Round of the General Agreement on Tariffs and Trade which included an agreement to reduce subsidies paid to farmers. This is underpinned by the WTO enforcement of agricultural subsidy, tariffs, import quotas and settlement of trade disputes that cannot be bilaterally resolved. Where trade barriers are raised on the disputed grounds of public health and safety, the WTO refer the dispute to the Codex Alimentarius Commission, which was founded in 1962 by the United Nations Food and Agriculture Organization and the World Health Organization.

Food retailing

World Health Organization The sale of surplus food traditionally took place once a week when farmers took their wares on market day, into the local village market place. Here food was sold to grocers for sale in their local shops for purchase by local people. With the onset of industrialisation, and the development of the food processing industry, a wider range of food could be sold and distributed in distant locations. Typically early grocery shops would be counter-based shops, in which purchasers told the shop-keeper what they wanted, so that the shop-keeper could get it for them. In the 20th century supermarkets were born. Supermarkets brought with them a self-service approach to shopping using shopping carts (or Trollies in Commonwealth English) and were able to offer quality food at lower cost, through economies of scale and reduced staffing costs. This was sometimes known as 'pile it high' In the latter part of the 20th century, this has been further revolutionised by the development of vast warehouse sized out-of-town supermarkets, selling an extraordinarily wide range of food from around the world. Unlike food processors, food retailing is a two-tier market in which a small number of very large companies control a large proportion of supermarkets. The supermarket giants wield great purchasing power over farmers and processors, and strong influence over consumers. Nevertheless, in 2000 only 19% of all US consumer expenditure spent on food went to farmers. Recent technological innovations such as point of sale technology - barcodes. This allows ordering of goods and food to be driven by actual sales.

Food sufficiency

Food deprivation leads to malnutrition and ultimately starvation. This is often connected with famine, which involves the absence of food in entire communities. This can have a devastating and widespread effect on human health and mortality. In 2003 it was estimated that each year, 40 million people die of hunger worldwide. Rationing is sometimes used to distribute food in times of shortage, most notably during times of war. Food deprivation is regarded as a deficit need in Maslow's hierarchy of needs and is measured using famine scales.

Food aid

Food aid can benefit people suffering from a shortage of food. Conversely, badly managed food aid can cause problems by disrupting local markets, depressing crop prices and discouraging food production. Its provision, or threatened withdrawal, is sometimes used as a political tool to influence the politics of the destination country. International efforts to distribute food to the neediest countries are co-ordinated by the World Food Programme. :See also: Fair trade, food security.

Food safety

Foodborne illness, commonly called "food poisoning," is caused by bacteria, toxins, viruses and prions. Food poisoning has been recognised as a disease of man since as early as Hippocrates. Murder by food poisoning was used during the Roman Empire. In the Middle Ages all Royal Courts had food tasters. The sale of rancid, contaminated or adulterated food was commonplace until introduction of hygiene, refrigeration, and vermin controls in the 19th century. Discovery of techniques for killing bacteria using heat and other microbiological studies by scientists such as Louis Pasteur contributed to the modern sanitation standards that we enjoy today. This was further underpinned by the work of Justus von Liebig whose work led to the development of modern food storage and food preservation methods. The two most common factors leading to cases of bacterial foodborne illness are cross-contamination of ready-to-eat food from other uncooked foods and improper temperature control. Less commonly, acute adverse reactions can also occur if chemical contamination of food occurs, for example from improper storage, or use of non-food grade soaps and disinfectants. Food can also be adulterated by a very wide range of articles (known as 'foreign bodies') during farming, manufacture, cooking, packaging, distribution or sale. For example, pests (or their feces), hairs, cigarette butts, wood chips, metal shards, plasters etc. It is possible for certain types of food to become contaminated if stored or presented in an unsafe container, such as a ceramic pot with lead-based glaze. Understanding of the causes of food-borne-illnesses and more systematic techniques for their elimination has led to the development of commercial systems such as HACCP which can, if properly implemented, identify and eliminate many, but not all, possible risks. HACCP is well suited to identifying and controlling these potential food safety risks.

Food allergies

Some people have food allergies or sensitivities to foods which are otherwise wholesome to the majority of people. The amount of the food substance required to provoke a reaction in a susceptible individual can be minute. For instance, tiny amounts of food in the air, too minute to be smelled, have been known to provoke lethal reactions in sufficiently sensitive individuals. In theory, any food may provoke a reaction, however, this most commonly involves gluten, corn, shellfish (mollusks), peanuts, and soy. Most patients present with diarrhea after ingesting certain foodstuffs, skin symptoms (rashes), bloating, vomiting and regurgitation. The digestive complaints usually develop within half an hour of ingesting the allergen. Rarely, food allergy can lead to anaphylactic shock: hypotension (low blood pressure) and loss of consciousness. This is a medical emergency. An allergen associated with this type of reaction is peanut, although latex products can induce similar reactions. Initial treatment is with epinephrine (adrenaline), often carried by known patients in the form of an Epi-pen. Food allergy is thought to develop easier in patients with the atopic syndrome, a very common combination of diseases: allergic rhinitis and conjunctivitis, eczema and asthma. The syndrome has a strong inherited component; a family history of these diseases can be indicative of the atopic syndrome.

Dietary habits

Dietary habits play a significant role in the health and mortality of all humans. For example:
- Eating disorders are a group of mental disorders that interfere with normal food consumption. They often affect people with a negative body image;
- 13% of the world's population suffer from Iodine deficiency;
- In 2003 it was estimated that vitamin A deficiency causes blindness in up to 500,000 children each year;
- Vitamin C deficiency results in scurvy;
- Calcium, Vitamin D and Phosphorus are inter-related. The consumption of each may affect the absorption of the others.
- Kwashiorkor and marasmus are childhood disorders caused by lack of dietary protein.
- Obesity, a serious problem in the western world, leads to higher chances of developing heart disease, diabetes, and many other diseases. Concerns about foodborne illness have long influenced diet. Traditionally humans have learned to avoid foods that induce acute illness. Some believe that this is the underlying rationale behind some traditional religious dietary requirements. Additionally, many people choose to forgo food from animal sources to varying degrees; see vegetarianism, veganism, fruitarianism, living foods diet, and raw foodism. The nutrient content of diets in industrialised countries contain more animal fat, sugar, energy, alcohol and less dietary fiber, carbohydrates and antioxidants. Contemporary changes to work, family and exercise patterns, together with concerns about the effect of nutrition and overeating on human health and mortality are all having an effect on traditional eating habits. Physicians and alternative medicine practitioners may recommend changes to diet as part of their recommendations for treatment. More recently, dietary habits have been influenced by the concerns that some people have about the chronic impact on health that arise through the consumption of genetically modified food. Further concerns about the impact of industrial farming on animal welfare, human health and the environment are also having an effect on contemporary human dietary habits. This has led to the emergence of a counterculture with a preference for organic and local food. :See also: Food faddism, Health claims on food labels, list of diets, Slow Food.

Nutrients in food

- Calcium
- Carbohydrate
- Essential amino acids
- Fat
- Iron
- Minerals
- Phytochemicals, including anti-oxidants, enzymes, bio-flavinoids
- Potassium
- Protein
- Sodium
- Starch
- Vitamins
- Water Category:Nutrition Category:Biology

Organ meat

Offal is the entrails and internal organs of a butchered animal. The word does not refer to a particular list of organs, but includes most internal organs other than muscles or bones. In many parts of the United States these portions of the animal tend to be considered "waste parts", although there are U.S. recipes which include chitterlings, hog maw, etc. The parts that constitute offal vary with time, place and cultural tradition. Many items classified as offal are considered to be delicacies, and command a high price, in many places: tongue, sweetbreads, calf's liver, etc. Offal may be used for human consumption as food, or, often after processing in a rendering plant, for animal feed, fertilizer or fuel. In some parts of Europe, brain, chitterlings or andouilles (pig's large intestine), feet or trotters, gizzard (bird's crop), heart, head (of pigs or calves), kidney, liver, lights (lung), sweetbreads (thymus or pancreas), tongue and tripe (stomach lining) from various mammals are common menu items. The traditional Scottish haggis consists of sheep stomach stuffed with a boiled mix of liver, heart, lungs, rolled oats and other ingredients. In the UK Midlands faggots are made from ground or minced pig offal (mainly liver and cheek), bread, herbs and onion wrapped in pig's caul. In Greece, splinantero consists of liver, spleen and small intestine, roasted over an open fire. A festive variety is kokoretsi: pieces of lamb or kid offal (liver, heart, lungs, spleen, kidney and fat) are pierced on a spit and covered by washed small intestine wound around in a tube-like fashion. Kokoretsi is then roasted over coal fire. It is a traditional Easter feature food. Another traditional Easter food is Mageiritsa: a soup made with lamb or kid's offal and lettuce in a white sauce. Tzigerosarmas and Gardoympa are two varieties of splinantero and kokoretsi made in different sizes and with extra spices to improve the taste. In some Latin American countries, cow stomach or intestine is used to make menudo, chinchulines ortripas; in others, like Peru, cow heart is used for anticuchos - a sort of brochettes. In Brazil, churrasco often includes chicken hearts, roasted in a big skewer. In China many more organs and animal-parts are used for food or medicine. In the United States offal is less often used for human consumption; when it is used, the euphemism "variety meats" is generally used. When offal is included as an ingredient in animal feed, it is listed under the name "meat byproducts", one of a number of ingredients that may be so listed. Certain organs of certain animals are unsafe to consume. The liver of Polar bear and other polar animals is so high in vitamin A that it can have a toxic effect on human metabolism. Some animal intestines may be very high in coliform bacteria and need to be washed and cooked thoroughly to be safe for eating. Other offal (especially nervous tissue) may be contaminated with TSE prions; in some jurisdictions these offal classified as specified risk materials are subject to special regulations. Offal is usually very high in purines. People suffering from gout should avoid offal in their diet. In American English, the words offal and awful are virtually homonyms — one dictionary shows the pronunciation of awful as being the same as the most-frequent pronunciation of offal — a fact which offers opportunity for some really bad puns.

External links

- [http://www.bartleby.com/61/70/O0037000.html Pronunciation of offal]
- [http://www.bartleby.com/61/28/A0552800.html Pronunciation of awful]
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Seafood

:For the band, see Seafood (band). Seafood (band) Seafood (band).]] Seafood is any sea animal that is served as food or is suitable for eating. This usually includes sea water animals, such as fish and shellfish (including mollusks, and crustaceans). By extension, the term seafood is also applied to similar animals from fresh water. These aquatic animals are also collectively referred to as seafood. Edible seaweeds are rarely considered seafood, even though they come from sea water and are widely eaten around the world. See :Category:Sea vegetables. The harvesting of seafood is known as fishing and the cultivation of seafood is known as aquaculture or mariculture. Also see fish farming. According to traditional Jewish food regulations, seafood falls into the category of ritually unclean and therefore does not conform to the kosher diet.

History

From the earliest age of human civilization, seafood has been an important food source that can easily be hunted and gathered even by those lacking power or speed. Basket-like traps have long been widely used to hunt fish in rivers and lakes. Sometimes, fish was speared just as one would hunt a small animal. Ancient Egyptian civilization used the symbol of fish for counting large numbers and it was eaten both dried and fresh. It is looked over too often but the rise of ancient Greek and Roman civilization was in no small part due to the abundant fish of the Mediterranean Sea. Shellfish was a staple food in many locations and in the Jomon period of Japan; the amount of shellfish consumed and thrown away from that time is used to measure how many people lived in certain area.

Dishes

Seafood is a source of protein in many diets around the world.
- Bouillabaisse
- Cioppino
- Clam chowder
- Fried squid
- Steamed fish
- Sushi

External links

- [http://wikibooks.org/wiki/Cookbook Wikibooks Cookbook]
- [http://www.salmonrecipes.net Over 700 salmon recipes]
- [http://www.completerecipes.com/seafood.htm Complete Recipes: Seafood]
- [http://www.absoluterecipes.com/seafood/ Absolute Recipes: Seafood]
- [http://www.find-a-seafood-recipe.com Seafood Recipe Site]
- [http://www.sushifaq.com The Sushi FAQ]
- [http://sushiotaku.blogspot.com/ The Sushi Otaku Blog]
- simple:Seafood

Meat market

The term meat market was was coined in the 1950s, and refers to a place where one goes for a casual sexual encounter, such as a bar or night club. Sex has been likened to meat since as early as the 16th century with such references to it as "have a jumble in the giblits" and "have a bit of mutton", not to mention "carnal relations."

Domesticate

Domesticated animals, plants, and other organisms are those whose collective behavior, life cycle, or physiology has been altered as a result of their breeding and living conditions being under human control for multiple generations. Humans have brought these populations under their care for a wide range of reasons: for help with various types of work, to produce food or valuable commodities (such as wool, cotton, or silk), and to enjoy as pets or ornamental plants. In a related way the notion of domestication is used in domestication theory that describes the process of the 'taming' or appropriation of technology by its users.

Process of domestication

There is debate within the scientific community over how the process of domestication works. Some researchers give credit to natural selection, wherein mutations outside of human control make some members of a species more compatible to human cultivation or companionship. Others have shown that carefully controlled selective breeding is responsible for many of the collective changes associated with domestication. These categories are not mutually exclusive and it is likely that natural selection and selective breeding have both played some role in the processes of domestication throughout history. The domestication of wheat provides an example of how natural selection and mutation can play a key role in the process. Wild wheat falls to the ground to reseed itself when it is ripe, but domesticated wheat stays on the stem when it is ripe. There is evidence that this critical change came about as a result of a random mutation near the beginning of wheat's cultivation. Wheat with this mutation was much more useful to farmers and became the basis for the various strains of domesticated wheat that have since been developed. The example of wheat has led some to speculate that mutations may have been the basis for other early instances of domestication. It is speculated that a mutation made some wolves less wary of humans. This allowed these wolves to start following humans to scavenge for food in their garbage dumps. Presumably something like a symbiotic relationship developed between humans and this population of wolves. The wolves benefited from human food scraps, and humans may have found that the wolves could warn them of approaching enemies, help with hunting, carry loads, provide warmth, or supplement their food supply. As this relationship evolved, humans eventually began to raise the wolves and breed the types of dogs that we have today. Nonetheless, some researchers maintain that selective breeding rather than mutation or natural selection best explains how the process of domestication typically worked. Some of the most well-known evidence in support of selective breeding comes from an experiment by Russian scientist, Dmitri Belyaev, in the 1950s. His team spent many years breeding the silver fox (Vulpes vulpes) and selecting only those individuals that showed the least fear of humans. Eventually, Belyaev's team selected only those that showed the most positive response to humans. He ended up with a population of grey fox whose behavior and appearance was significantly changed. These foxes no longer showed any fear of humans and often wagged their tails and licked their human caretakers to show affection. Despite the success of this experiment, it is clear that selective breeding cannot always achieve domestication. Attempts to domesticate several kinds of wild animals in this way have failed repeatedly. The zebra is one example. The historical process of domestication cannot be fully explained by any one principle acting alone. Some combination of natural selection and selective breeding has played a role in the domestication of the various species that humans have come into close contact with throughout history.

Domestication of animals

According to physiologist Jared Diamond, animal species must meet six criteria in order to be considered for domestication: #Flexible diet — Creatures that are willing to consume a wide variety of food sources and can live off less cumulative food from the food pyramid are less expensive to keep in captivity. Most carnivores can only be fed meat, which requires the expenditure of many herbivores. #Reasonably fast growth rate — Fast maturity rate compared to the human life span allows breeding intervention and makes the animal useful within an acceptable duration of caretaking. Large animals such as elephants require many years before they reach a useful size. #Ability to be bred in captivity — Creatures that are reluctant to breed when kept in captivity do not produce useful offspring, and instead are limited to capture in their wild state. Creatures such as the panda and cheetah are difficult to breed in captiv