Peccaries are wild pigs (order Artiodactyla, family Tayassuidae) of the New World which are relatives of the wild pigs of the Old World. Peccaries are the only pigs native to the New World pigs, all other pigs in North and South America are formerly domestic animals that have escaped and become feral. Taxonomists recognize three species of peccaries: the collared peccary (Tayassu tajacu) of the so…
In genetics, a pedigree is a diagram of a family tree showing the relationships between individuals together with relevant facts about their medical histories. A pedigree analysis is the interpretation of these data that allows a better understanding of the transmission of genes within the family. Usually, at least one member of the family has a genetic disease, and by examining the pedigree, clue…
Pelicans are large coastal birds belonging to order Pelecaniformes, along with gannets, tropicbirds, darters, frigatebirds, and cormorants. All of them have throat pouches to one extent or another, but only the pelicans' are so big. They eat nothing but fish, and the pouch is a handy device for catching their food. The pelican has perhaps the most unusual bill in the bird world. It is quite…
Penguins are primitive, flightless birds that are highly specialized for marine life. Most species look A gentoo penguin with its chick. JLM Visuals. Reproduced by permission. rather similar, being generally dark-blue or dark-gray on top with a white belly. Some species, however, have a crest on their head and/or patches of color on their head and throat. The legs are set wide apart and …
A peninsula is a piece of land surrounded by water on three sides and joined to a larger body of land by an isthmus, or neck. A peninsula is a topographic high spot; a dry land range of hills or mountains created during the formation of the earth's crust. It is left visible when the low areas on both sides either subside and become submerged, or when the water level rises and floods the val…
Pentyl or five carbon atom alkyl groups are also referred to as amyl groups. The term amyl is derived from the Latin word for starch, amylum, and is used because the five carbon atom amyl alcohols were first isolated from fermentation products. Amyl or pentyl alcohols consist of a chain of five carbon atoms with a hydroxyl group (-OH) connected to one of the carbon atoms. Each carbon atom is also …
The peony is an attractive flower, much beloved of gardeners. It is in the family Paeonaceae, though in the past it was in the family Ranunculaceae with other flowers such as the buttercup. The generic name is Paeonia and there are some 50 species in this group. The name peony comes from Paeon, a physician in Greek mythology. His teacher was jealous of his skills as a healer and intended to murder…
Pepper, one of the world's most important spices, comes from the fruit (peppercorns) of a flowering shrub, in the genus Piper, family Piperceaea. The pepper plant originates from India, which is still the world's largest producer of pepper. The plant grows in hot, humid regions such as India, Indonesia, Malaysia, and Brazil. The United States is the world's largest importer of…
Proteins are made up of amino acids, which are joined by peptide linkages. Although there are only 20 different naturally occurring amino acids, various combinations of these form the thousands of proteins used in metabolism. All amino acids have a similar structure. There is a central carbon atom, called the alpha-carbon and this is bonded to an amino group on one side and a carboxyl group on the…
Human perception is the active reception and coordination of information received through our sensory systems in order to make sense of the environment and to behave effectively within it. In contrast with the direct and immediate sensations actually received and transmitted, perception is the transformation of that information into nerve cell activity that is transferred to the brain where furthe…
Perch belong to the class Osteicthyes, whose members have a skeleton of bone rather than cartilage. Bony fish comprise the largest group of vertebrates living today, both in the number of individuals (millions) and in the number of species (about 30,000). Perch occur in both fresh water and sea water throughout the entire world. Perch live at depths in the oceans as great as 7 mi (11.5 km) and in …
The peregrine falcon (Falco peregrinus) is a bird of prey in the family Falconidae. It is one of the most wide-ranging birds in the world with populations in both the Eastern and Western Hemispheres, and occurring on all continents except Antarctica. It is also the world's fastest-flying bird. Unfortunately, beginning in the 1940s, many populations of the peregrine falcon were decimated by …
A perfect number is a whole number which is equal to the sum of its divisors including 1 by excluding the number itself. Thus 6 is a perfect number becauses 1 + 2 + 3 = 6. Likewise 28 is a perfect number because 1 + 2 + 3 + 4 + 7 + 14 = 28. The search for even perfect numbers, then, is the same as the search for Mersenne primes. At the present time 32 are known corresponding to p = 2, 3, 7, 13,...…
A periodic function is a function whose values repeat at regular intervals. Given an interval of length t, and a function f, if the value of the function at x + t is equal to the value of the function at x then f is a periodic function. In standard function notation this is written f(x + t) = f(x) (read "f of x plus t equals f of x"). The shortest length t for which the function repe…
The arrangement of the chemical elements into periods (horizontal rows) and groups (vertical columns) is called the periodic table. The elements in the table are represented by symbols (one, two, or three letters) in individual squares. Above each chemical symbol appears the atomic number of the element. These whole numbers are the number of protons present in the nucleus of that element. Below th…
Periodization, which became a branch of historical method and the philosophy of history in the twentieth century, has to do with the division of time's arrow—the theoretical timeline of the movement from past to present and future. In Western tradition this speculative aspect of history has its roots in myth and in the Bible—in Hesiod's succession of gold, silver, and b…
Notions of boundaries, categories, and periods frame discussions of art and visual culture. The desire to organize visual information and material into clearly defined, manageable units has provided an irresistible impetus for periodization since the emergence of art historical and critical studies in the Renaissance. The application of periods to art and visual culture was extended in the ninetee…
Geologists define permafrost as soil layers or rock and soil combinations that remain frozen (i.e., remain below the specific freezing temperature unique to the exact constituents of the formation) for a time period in excess of two years. The exact composition of permafrost can vary widely depending on the unique geology and morphology of the area in which the perafrost forms. Although ice is usu…
The term perpendicular describes a pair of lines or planes that intersect each other at a 90 degree angle. Perpendicularity is an important concept in mathematics, science, and engineering. A line l1 is perpendicular to a line l2 if the two intersect with congruent adjacent angles, which means that the angles are both equal to 90 degrees. Of course, a purely analytical definition of the term exist…
Western European ideas about the person have long centered on the duality between body and soul (in religious discourse) or between body and mind (in the domains of philosophy and psychology). Consequently, early anthropological interest in non-European ideas of the person tended to mirror such deep-seated European conceptualizations, focusing on the origins of the concept of the soul. The preoccu…
Although identity has deeps roots in social psychology, sociology, bridges between them (e.g., symbolic interactionism), and related disciplines, the explicit distinction between personal and social identity, within social psychology at least, can be traced to J. C. Turner's seminal article "Towards a Cognitive Redefinition of the Group" (1982). This formed the basis for self-…
What is a person? Two basic types of considerations are apparent in African answers to this question. The first is ontological, the second ethical. Ontologically a person is a combination of a physical constituent, namely the body and a set of two or in some cases three constituents of a rarefied character requiring careful elucidation. The nonbodily constituent on which all the accounts of person…
A pesticide is a chemical that is used to kill insects, weeds, and other organisms to protect humans, crops, and livestock. A broad-spectrum pesticide that kills all living organisms is called a biocide. Fumigants, such as ethylene dibromide or dibromochloropropane, used to protect stored grain or sterilize soil fall into this category. Generally, however, we prefer narrower spectrum agents that a…
Pests are any organisms that are considered, from the perspective of humans, to be undesirable in some ecological context. For example, pests could be insects that compete with humans for some common resource, such as agricultural production or timber. Other pests might be associated with diseases of humans, livestock, or agricultural plants. Pests could also be unwanted weeds that compete with ag…
Petrels and shearwaters are wide-ranging oceanic birds with a characteristic tubenose and other specialized features that equip them well for a life spent mostly at sea. Found throughout the world, these long-lived colonial nesting seabirds include some 79 species in four families, all in the Order Procelliformes. These seabirds show a great range in body size, from the giant petrel with a 6 ft (2…
Petroleum is a term that includes a wide variety of liquid hydrocarbons. Many scientists also include natural gas in their definition of petroleum. The most familiar types of petroleum are tar, oil, and natural gas. Petroleum forms through the accumulation, burial, and transformation of organic material, such as the remains of plants and animals, by chemical reactions over long periods of time. Af…
pH is a measure of the acidity or alkalinity of a solution based upon the dissociation of water. The variability of pH can have a dramatic effect on biological or physical chemical reactions (e.g., geochemical weathering processes). The pH scale was developed by Danish chemist Søren Peter Lauritz Sørensen (1868–1939) in 1909 and is generally presented as ranging from 0&#x…
Phalangers are a small group of arboreal mammals belonging to the family Phalangeridae, of which 20 species are recognized in six genera. Phalangers, more commonly known as possums and cuscuses, are marsupials but with a vague resemblance to some monkeys. Indeed many early European explorers thought that they were monkeys. These species occur in Australia, New Guinea and adjacent islands west to S…
Pharmacogenetics is the exploration of the relationship between inherited genes and the ability of the body to metabolize drugs. Although research interests are rapidly expanding, by early 2003 pharmacogenetics research concentrated on trying establish connections between the genes carried by an individual (genotype) and specific reactions to drugs (e.g., side effects, toxicities, etc.). Modern me…
Pheasants are large species of fowl in the family Phasianidae, which also includes the partridges, peafowl, guinea fowl, francolins, and quail. The greatest diversity of pheasants occurs in Asia, but native species also occur in Africa and Europe. In addition, many species of pheasants have been widely introduced as gamebirds beyond their natural range. Pheasants are also kept as handsome showbird…
Phenomenology is the study of experience, how things appear to us. The word comes from the Greek but was elaborated in the early nineteenth century on the basis of Immanuel Kant's conception of the world as phenomenon, the world of our experience (as opposed to the world as noumenon, the world as it is "in itself"). Georg Wilhelm Friedrich Hegel famously employed the term in P…
In the left-hand representations, the benzene molecule is drawn as a hexagon with alternating single and double bonds. This is a shorthand method of drawing compounds used by chemists. A carbon atom is represented by an intersection of two straight lines or at the end of a line and the correct number of hydrogen atoms to give each carbon atom four bonds is implied but not drawn. The two equivalent…
Phenylketonuria (PKU) is an inherited disorder in which an enzyme (usually phenylalanine hydroxylase) crucial to the appropriate processing of the amino acid, phenylalanine is totally absent or drastically deficient. The result is that phenylalanine cannot be broken down, and it accumulates in large quantities throughout the body. Normally, phenylalanine is converted to tyrosine. Because tyrosine …
Pheromones are volatile chemical compounds secreted by insects and animals. They act as chemical signals between individuals influencing physiology and behavior in a manner similar to hormones. Pheromones are important to a variety of behaviors including mate attraction, territorality, trail marking, danger alarms, and social recognition and regulation. The term pheromone is derived from the Greek…
Active in English usage by the seventeenth century, philanthropy has been shown more recently to have a long, complex, and controversial history displaying multiple meanings of the term. Now philanthropy is normally construed as love of mankind, a voluntary, practical benevolence toward others, or an effort to promote the welfare of humanity by gifts without self-benefit. However, philanthropy ove…
The dialectic between religious and secular philosophy and the split between those who think of philosophy as akin to poetry and those who insist that it be exact and rigorous are not the only oppositions that rend modern philosophy. There is also the perennial tug-of-war between those philosophers who stubbornly hold onto the ancient paradigm of philosophy as the more or less practical search for…
A respected Princeton philosopher keeps a sign on his office door forbidding the discussion therein of any philosophy more than ten years old. At this late stage in his career the restriction includes a good deal of his own work. This may well be the limit case of the antihistorical attitude that prevailed throughout much academic philosophy of the twentieth century, motivated by the view that phi…