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Definition: Species |
SpeciesNoun1. (biology) taxonomic group whose members can interbreed. 2. A specific kind of something: "a species of molecule"; "a species of villainy". Source: WordNet 1.7.1 Copyright © 2001 by Princeton University. All rights reserved. |
Date "species" was first used in popular English literature: sometime before 1321. (references) |
Etymology: Species \Spe"cies\, noun. singular plural [Latin expression, sight, outward appearance, shape, form, particular sort, kind, or quality, species. See Spice, noun, and compare to Specie, Special.]. (references) |
| Domain | Definition |
Agriculture | Species represent the lowest and most important of the primary groupings used in classifying plants, animals, and microorganisms. While no single definition applies to all organisms, biologists rely principally on (1) morphological and genetic similarities and (2), for sexually reproducing organisms, the capability of interbreeding with one another but not other groups. If different species do interbreed, the offspring, if any, are often sterile. Biologists give species unique, binomial names: a generic name that includes closely related species, and a species-specific name. The horse, for example, is Equus caballus; the donkey or ass is Equus asinus. (Their offspring, the mule, is sterile.) As populations of organisms vary geographically and change over time (becoming extinct, or splitting or evolving into new species), species classifications are neither absolute nor immutable; where some biologists see variations within a species (and may designate subspecies), others may see separate species. About 1.5 to 2 million species have been named, but scientists estimate the total number of species could be 5 to 100 million, many of them probably undiscovered microorganisms. The Endangered Species Act (ESA) protects species designated as endangered or threatened with extinction; these protections prohibit taking endangered species and can include restrictions on habitat alterations, such as logging or water pollution. Because of the way "species" is defined in the ESA, policy debates have arisen over whether certain groups of organisms qualify for listing (e.g., northern goshawks and the Alexander Archipelago wolf). (references) |
Avian | A group of actually or potentially interbreeding populations that are reproductively isolated from all other kinds of organisms (Ricklefs 1979:880). (references) |
Biology & Biotechnology | The main category of taxonomic classification into which genera are subdivided, comprising a group of similar interbreeding individuals sharing a common morphology, physiology, and reproductive process. Source: European Union. (references) |
| An organism which is, and remains, distinct because it does not normally interbreed with other organisms. Source: European Union. (references) | |
Environment | 1. A reproductively isolated aggregate of interbreeding organisms having common attributes and usually designated by a common name.2. An organism belonging to belonging to such a category. (references) |
Health | A taxonomic category subordinate to a genus (or subgenus) and superior to a subspecies or variety, composed of individuals possessing common characters distinguishing them from other categories of individuals of the same taxonomic level. In taxonomic nomenclature, species are designated by the genus name followed by a Latin or Latinized adjective or noun. (references) |
Information | A concept or a class is species of another concept or class if the latter is a genus of the first. Source: European Union. (references) |
Medicine | A popular name applied to certain herb preparations. Source: European Union. (references) |
Mining | A mineral distinguished from others by its unique chemical and physicalproperties; it may have varieties. (references) |
Source: compiled by the editor from various references; see credits. | |
(From Wikipedia, the free Encyclopedia)
Particle physics is a branch of physics that studies the elementary constituents of matter and radiations, and the interactions between them. It is also called high energy physics, because many elementary particles do not occur independently in Nature, and can only be detected during energetic collisions of larger particles, as is done in particle accelerators.
Modern particle physics research is focused on subatomic particles, which are smaller than atoms. These include atomic constituents such as electrons, protons, and neutrons (protons and neutrons are actually composite particles, made up of quarks), as well as particles produced by radiative and scattering processes, such as photons, neutrinos, and muons.
Strictly speaking, the term particle is something of a misnomer. The objects studied by particle physics obey the principles of quantum mechanics. As such, they exhibit wave-particle duality, displaying particle-like behavior under certain experimental conditions and wave-like behavior in others. Theoretically, they are described neither as waves nor as particles, but as state vectors in an abstract Hilbert space. For a more detailed explanation, see quantum field theory. Following the convention of particle physicists, we will use "elementary particles" to refer to objects such as electrons and photons, with the understanding that these "particles" display wave-like properties as well.
All the particles observed to date have been catalogued in a quantum field theory called the Standard Model, which is often regarded as particle physics' best achievement to date. The model contains 47 species of elementary particles, some of which can combine to form composite particles, accounting for the hundreds of other species of particles discovered since the 1960s. The Standard Model has been found to agree with almost all the experimental tests conducted to date. However, most particle physicists believe that it is an incomplete description of Nature, and that a more fundamental theory awaits discovery. In recent years, measurements of neutrino mass have provided the first experimental deviations from the Standard Model.
Particle physics has had a large impact on philosophy of science. The reductionist ideas that motivates much of the work in this field has been criticized by various philosophers and scientists. Part of the debate is described below.
History of particle physics
The idea that matter is composed on elementary particles dates to at least the 6th century BC. The philosophical doctrine of "atomism" was studied by ancient Greek philosophers such as Leucippus, Democritus, and Epicurus. Although Isaac Newton in the 17th century thought that matter was made up of particles, it was John Dalton who formally stated in 1802 that everything is made from tiny atoms.
Dmitri Mendeleev's first periodic table in 1869 helped cement the view, prevalent throughout the 19th century, that matter was made of atoms. Work by J.J. Thomson established that atoms are composed of light electrons and massive protons. Ernest Rutherford established that the protons are concentrated in a compact nucleus. The nucleus was initially thought to be composed of protons and confined electrons (in order to explain the difference between nuclear charge and mass number), but was later found to be composed of protons and neutrons.
The 20th century explorations of nuclear physics and quantum physics, culminating with proofs of nuclear fission and nuclear fusion, gave rise to an active industry of generating one atom from another, even rendering possible (although not feasible economically) the transmutation of lead into gold. These theories successfully predicted nuclear weapons.
Throughout the 1950s and 1960s, a bewildering variety of particles was found in scattering experiments. This was referred to as the "particle zoo". This term was deprecated after the formulation of the Standard Model during the 1970s in which the large number of particles was explained as combinations of a (relatively) small number of fundamental particles.
The Standard Model of particle physics
The current state of the classification of elementary particles is called the "Standard Model". It describes the strong, weak, and electromagnetic fundamental forces, using mediating bosons known as "gauge bosons". The species of gauge bosons are the photon, W- and W+ and Z bosons, and the gluons. The model also contains 24 fundamental particles, which are the constituents of matter. Finally, it predicts the existence of a type of boson known as the Higgs boson, which has yet to be discovered.
Experimental particle physics
In Particle Physics, the major international collaborations are:
Many other particle accelerators exist.
- CERN, located on the French-Swiss border near Geneva. Its main facilities are LEP, the Large Electron Positron collider (now dismantled) and the LHC, or Large Hadron Collider (under construction).
- DESY, located in Hamburg, Germany. Its main facility is HERA, which collides electrons or positrons and protons.
- SLAC, located near Palo Alto, USA. Its main facility is PEP-II, which collides electrons and positrons.
- Fermilab, located near Chicago, USA. Its main facility is the Tevatron, which collides protons and antiprotons.
- Brookhaven National Laboratory, located on Long Island, USA. Its main facility is the Relativistic Heavy Ion Collider, which collides heavy ions such as gold ions (it is the first heavy ion collider) and protons.
Objections against particle physics as reductionism
Within physics itself, there are some objections to the extreme reductionist approach of attempting to explain everything in terms of elementary particles and their interaction. These objections are usually raised by solid state physicists. While the Standard Model itself is not challenged, it is held that testing and perfecting the model is not nearly as important as studying the emerging properties of atoms and molecules, and especially large statistical ensembles of those. These critics claim that even a complete knowledge of the underlying elementary particles will not give complete knowledge of atoms and molecules, knowledge that arguably is more important to us.
Reductionists typically claim that all progress in the sciences has involved reductionism to some extent.
Public policy and particle physics
Experimental results in particle physics are investigated using enormous particle accelerators which typically cost several billion dollars and require large amounts of government funding. Because of this, particle physics research involves issues of public policy.
Many have argued that the potential advances do not justify the money spent, and that in fact particle physics takes money away from more important research and education efforts. In 1993, the US Congress stopped the Superconducting Super Collider because of similar concerns, after $2 billion had already been spent on its construction. Many scientists, both supporters and opponents of the SSC, believe that the decision to stop construction of the SSC was due in part to the end of the Cold War which removed scientific competition with the Soviet Union as a rationale to spend large amounts of money on the SSC.
Some within the scientific community believe that particle physics has also been adversely affected by the aging population. The belief is that the aging population is much more concerned with immediate issues of their health and their parent's health and that this has driven scientific funding away from physics toward the biological and health sciences. In addition, many opponents question the ability of any single country to support the expense of particle physics results and fault the SSC for not seeking greater international funding.
Proponents of particle accelerators hold that the investigation of the most basic theories deserves adequate funding, and that this funding benefits other fields of science in various ways. They point out that all accelerators today are international projects and question the claim that money not spent on accelerators would then necessarily be used for other scientific or educational purposes.
See also
- Subatomic particle
- Fundamental particle
- List of particles
External Links
- A site with more detail, and news from particle physics, and an Excellent (and comprehensive) graphical walkthrough
- GISAI glossary, Yudkowsky
- "Philosophy Redivivus? Science, Ethics, and Faith"
- History of particle physics
- Introduction to Particle Physics by Matthew Nobes (published on Kuro5hin): Part 1, Part 2, Part 3a, Part 3b
Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Particle physics."
(From Wikipedia, the free Encyclopedia)
Scientific classification refers to how biologists group and categorize extinct and living species of organisms. Modern classification has its roots in the system of Carl Linnaeus, who grouped species according to shared physical characteristics. These groupings have been revised since Linnaeus to improve consistency with the Darwinian principle of common descent. Genomic DNA analysis has driven many recent revisions and is likely to continue to do so. Scientific classification belongs to the science of taxonomy or biological systematics.
Early Systems
The earliest known system of classifying forms of life comes from the Greek philosopher Aristotle.
The next major advance in developing scientific classification was by the Swiss professor, Conrad Gessner (1516 - 1565). Gessner's work was a critical compilation of life known at the time.
The exploration of parts of the New World next brought to hand descriptions and specimens of many novel forms of animal life. In the latter part of the 16th century and the beginning of the 17th careful study of animals commenced, which, directed first to familiar kinds, was gradually extended until it formed a sufficient body of knowledge to serve as an anatomical basis for classification. Advances in using this knowledge to classify living beings bears a debt to the research of medical anatomists, such as Fabricius (1537 - 1619), Severinus (1580 - 1656), William Harvey (1578 - 1657), and Tyson (1649 - 1708). Advances in classification due to the work of entomologists and the first microscopists is due to the research of people like Marcello Malpighi (1628 - 1694), Jan Swammerdam (1637 - 1680), and Robert Hooke (1635 - 1702).
John Ray (1627 - 1705) was an English naturalist who published important works on plants, animals, and natural theology. His classification of plants in his Historia Plantarum was an important step towards modern taxonomy. Ray rejected the system of dichotomous division by which species were classified according to a pre-conceived, either/or type system, and instead classified plants according to similarities and differences that emerged from observation.
Linnaean taxonomy
Two years after John Ray's death Carolus Linnaeus (1707 - 1778) was born. His great work, the Systema Naturae, ran through twelve editions during his lifetime (1st ed. 1735). He is best known for his introduction of a method of modern classification; he created systematic zoology and botany in their present form. Linnaeus adopted Ray's conception of species, but he made the concept a practical reality by insisting that every species must have a unique Latin binomen, that is, a double name - the first half to be the name of the genus common to several species, and the second half to be a single word, which is called the specific epithet. This convention is now referred to as binomial nomenclature, and the name formed from the two parts is known as the scientific name of a species.
Before Linnaeus, long many-worded names had been used, sometimes with one additional adjective, sometimes with another, so that no true names were fixed and accepted. Linnaeus' system made it easy to identify unambiguously any given species of plant or animal. He proceeded further to introduce into his system a series of groups: genus, order, class.
The Linnaeus System works by placing each organism into a layered hierarchy of groups. Each group at a given layer is composed of a set of groups from the layer directly below. Simply knowing the two-part scientific name makes it possible to determine the other six layers.
The groupings (taxa) of taxonomy from most general to most specific are:
Several acronym mnemonics have been made for these, for instance King Phillip called out for good soup, or Kings Play Chess On Funny Green Squares.
- Kingdom
- Phylum (animals) or Division (plants)
- Class
- Order
- Family
- Genus
- Species
Intermediate ranks may be created by adding prefixes, for instance:
In addition, species are often subdivided into subspecies and other infraspecific categories (see subspecies). The term varieties is sometimes used in place of subspecies. In horticulture, for example, it refers to populations modified by selective breeding, for instance the Peace Rose, a hybrid Tea Rose.
- Superorder
- Order
- Suborder
- Infraorder
In husbandry, horticulture and other activities outside scientific biology, people still assume the truth of the traditional Linnaean system.
Modern developments
The approach Linnaeus took to classifying species and the majority of his taxonomic groupings remained the standard in biology for at least two centuries. Since the 1960s, however, a trend called cladism or cladistic taxonomy, has emerged and is expected to supplant Linnaean classification. In classifying species, cladists place a priority in achieving coherence with the Darwinian principle of common descent.
Meanwhile, at the top of the hierarchy of classification, there has movement towards a three domain system. The domains originally were replacements for the different kingdoms, but many scientists regard them as a groupings above the formerly paramount kingdom level.
Cladistics
In grouping species, cladists look for "derived similarities," meaning those aspects that species can be expected to share by virtue of a common evolutionary ancestry. This approach differs from that of phenetics, which does not address ancestry and associates species based on overall similarity, and it differs also from classification based on ad hoc "key characters." Cladists avail themselves of all types of information available, including DNA sequences and hybridization studies, biochemistry, and traditional morphology. They often make use of computers to identify the most likely phylogeny or "family tree" that relates the species they are considering.
Cladistics requires taxa (groups of species) to be clades. A formal code of phylogenetic nomenclature, the Phylocode[1], is currently under development for a cladistic taxonomy that abandons the Linnaean structure.
More at: cladistics.
Could add a description of the difficulty in classifying microbes: their features are derived from direct visual observation, but include such procedural characteristics as Gram stain type, motility, ability to form spores, etc. However, given an unknown bacterium with a given set of characteristics, it is in general not possible to predict its phylogeny, toxicity, etc. Other methods, using genes, their DNA, and several types of RNA, are under development.
Kingdom Animalia Phylum Arthropoda Class Insecta Order Diptera Family Drosophilidae Genus Drosophila Species melanogaster
Kingdom Animalia Phylum Chordata Subphylum Vertebrata Class Mammalia Subclass Eutheria Order Primates Suborder Catarrhini Family Hominidae Genus Homo Species sapiens
Cucumbertree (Magnolia acuminata)
Kingdom Plantae Division Magnoliophyta Class Magnoliopsida Order Magnoliales Family Magnoliaceae Genus Magnolia Species acuminata Note in this last example, that most of the taxa are named after the type genus, Magnolia.
Taxon Plants Algae Fungi Animals Division/Phylum -phyta -phyta -mycota Subdivision/Subphylum -phytina -phytina -mycotina Class -opsida -phyceae -mycetes Subclass -idae -phycidae -mycetidae Order -ales -ales -ales Suborder -ineae -ineae -ineae Superfamily -acea -acea -acea -oidea Family -aceae -aceae -aceae -idae Subfamily -oideae -oideae -oideae -inae Tribe -eae -eae -eae -ini Subtribe -inae -inae -inae -ina
See also:
- Binomial nomenclature
- Taxonomy
- List of biological orders
- List of Latin and Greek words commonly used in systematic names
- Phylogenetic tree
External Links:
- Classification of Animals
- Phylocode - replacing older system with Cladistic system
Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Scientific classification."
(From Wikipedia, the free Encyclopedia)
This article deals with the biological usage of the term. See combinatorial species for a mathematical usage.Species is a taxonomic concept used in biology to refer to a population of organisms that are in some important ways similar. The idea of species has a long history. After thousands of years of use, the concept remains central to biology and a host of related fields, and yet also remains at times ill-defined and controversial. There are several main lines of thought in the definition of species:
In practice, these definitions often coincide, and the differences between them are more a matter of emphasis than of outright contradiction. Nevertheless, no species concept yet proposed is entirely objective, or can be applied in all cases without resorting to judgement.
- A morphological species is a group of organisms that have a distinctive form: for example, we can distinguish between a chicken and a duck because they have different shaped bills and the duck has webbed feet. Species have been defined in this way since well before the beginning of recorded history. Although much criticised, the concept of morphological species remains the single most widely used species concept in everyday life, and still retains an important place within the biological sciences, particularly in the case of plants.
- The biological species or isolation species concept identifies a species as a set of actually or potentially interbreeding organisms. This is generally the most useful formulation for scientists working with living examples of the higher taxa like mammals, fish, and birds, but meaningless for organisms that do not reproduce sexually. It distinguishes between the theoretical possibility of interbreeding and the actual likelihood of gene flow between populations. For example, it is possible to cross a horse with a donkey and produce offspring, however they remain separate species—in this case for two different reasons: first because horses and donkeys do not normally interbreed in the wild, and second because the fruit of the union is rarely fertile. The key to defining a biological species is that there is no significant cross-flow of genetic material between the two populations.
- A mate-recognition species is defined as a group of organisms that are known to recognise one another as potential mates. Like the isolation species concept above, it is not applicable to organisms that do not reproduce sexually.
- A phylogenetic or evolutionary or Darwinian species is a group of organisms that shares a common ancestor; a lineage that maintains its integrity with respect to other lineages through both time and space. At some point in the progress of such a group, members may diverge from one another: when such a divergence becomes sufficiently clear, the two populations are regarded as separate species.
The naming of a particular species should be regarded as a hypothesis about the evolutionary relationships and distinguishability of that group of organisms. As further information comes to hand, the hypothesis may be confirmed or refuted. As a result of the revolutionary (and still ongoing) advance in microbiological research techniques in the later years of the 20th century, a great deal of extra knowledge about the differences and similarities between species has become available. Many populations which were formerly regarded as separate species are now considered to be a single biological unit, and many formerly grouped populations have been split. At higher taxonomic levels, these changes have been still more profound.
The isolation species concept in more detail
In general, for large, complex, organisms that reproduce sexually (such as mammals and birds) one of several variations on the isolation or biological species concept is employed. Often, the distinction between different species, even quite closely related ones, is simple. Horses (Equus caballus) and donkeys (Equus asinus) are easily told apart even without study or training, and yet are so closely related that they can interbreed after a fashion. Because the result, a mule or hinny, is not usually fertile, they are clearly separate species.
But many cases are more difficult to decide. This is where the isolation species concept diverges from the evolutionary species concept. Both agree that a species is a lineage that maintains its integrity over time, that is diagnosably different to other lineages (else we could not recognise it), is reproductively isolated (else the lineage would merge into others, given the chance to do so), and has a working intra-species recognition system (without which it could not continue). In practice, both also agree that a species must have its own independent evolutionary history—otherwise the characteristics just mentioned would not apply. The species concepts differ in that the evolutionary species concept does not make predictions about the future of the population: it simply records that which is already known. In contrast, the isolation species concept refuses to assign the rank of species to populations that, in the best judgement of the researcher, would recombine with other populations if given the chance to do so.
The isolation question
There are, essentially, two questions to resolve. First, is the proposed species consistently and reliably distinguishable from other species? Secondly, is it likely to remain so in the future? To take the second question first, there are several broad geographic possibilities.
- The proposed species are sympatric—they occupy the same habitat. Observation of many species over the years has failed to establish even a single instance of two diagnostically different populations that exist in sympatry and have then merged to form one united population. Without reproductive isolation, population differences cannot develop, and given reproductive isolation, gene flow between the populations cannot merge the differences. This is not to say that cross breeding does not take place at all, simply that it has become negligible. Generally, the hybrid individuals are less capable of successful breeding than pure-bred individuals of either species.
- The proposed species are allopatric—they occupy different geographical areas. Obviously, it is not possible to observe reproductive isolation in allopatric groups directly. Often it is not possible to achieve certainty by experimental means either: even if the two proposed species interbreed in captivity, this does not demonstrate that they would freely interbreed in the wild, nor does it always provide much information about the evolutionary fitness of hybrid individuals. A certain amount can be inferred from other experimental methods: for example, do the members of population A respond appropriately to playback of the recorded mating calls of population B? Sometimes, experiments can provide firm answers. For example, there are seven pairs of apparently almost identical marine snapping shrimp (Altheus) populations on either side of the Isthmus of Panama (which did not exist until about 3 million years ago). Until then, it is assumed, they were members of the same 7 species. But when males and females from opposite sides of the isthmus are placed together, they fight instead of mating. Even if the isthmus were to sink under the waves again, the populations would remain genetically isolated: therefore they are now different species. In many cases, however, neither observation nor experiment can produce certain answers, and the determination of species rank must be made on a 'best guess' basis from a general knowledge of other related organisms.
- The proposed species are parapatric—they have breeding ranges that abut but do not overlap. This is fairly rare, particularly in temperate regions. The dividing line is often a sudden change in habitat (an ecotone) like the edge of a forest or the snow line on a mountain, but can sometimes be remarkably trivial. The parapatry itself indicates that the two populations occupy such similar ecological roles that they cannot coexist in the same area. Because they do not crossbreed, it is safe to assume that there is a mechanism, often behavioral, that is preventing gene flow between the populations, and therefore that they should be classified as separate species.
- There is a hybrid zone where the two populations mix. Typically, the hybrid zone will include representatives of one or both of the 'pure' populations, plus first-generation and back-crossing hybrids. The strength of the barrier to genetic transmission between the two pure groups can be assessed by the width of the hybrid zone relative to the typical dispersal distance of the organisms in question. (The dispersal distance of oaks, for example, is the distance that a bird or squirrel can be expected to carry an acorn; the dispersal distance of Numbats is about 15 kilometres, as this is as far as young Numbats will normally travel in search of vacant territory to occupy after leaving the nest.) The narrower the hybrid zone relative to the dispersal distance, the less gene flow there is between the population groups, and the more likely it is that they will continue on separate evolutionary paths. Nevertheless, it can be very difficult to predict the future course of a hybrid zone; the decision to define the two hybridizing populations as either the same species or as separate species is difficult and potentially controversial.
- The variation in the population is clinal—at either extreme of the population's geographic distribution, typical individuals are clearly different, but the transition between them is seamless and gradual. For example, the Koalas of northern Australia are clearly smaller and lighter in colour than those of the south, but there is no particular dividing line: the further south an individual Koala is found, the larger and darker it is likely to be; Koalas in intermediate regions are intermediate in weight and colour. In contrast, over the same geographic range, black-backed (northern) and white-backed (southern) Australian Magpies do not blend from one type to another: northern populations have black backs, southern populations white backs, and there is an extensive hybrid zone where both 'pure' types are common, as are crossbreeds. The variation in Koalas is clinal (a smooth transition from north to south, with populations in any given small area having a uniform appearance), but the variation in magpies is not clinal. In both cases, there is some uncertainty regarding correct classification, but the consensus view is that species rank is not justified in either. The gene flow between northern and southern magpie populations is judged to be sufficiently restricted to justify terming them subspecies (not full species); but the seamless way that local Koala populations blend one into another shows that there is substantial gene flow between north and south. As a result, experts tend to reject even subspecies rank in this case.
The difference question
Obviously, when defining a species, the geographic circumstances become meaningful only if the populations groups in question are clearly different: if they are not consistently and reliably distinguishable from one another, then we have no grounds for believing that they might be different species. The key question in this context, is "how different is different?" and the answer is usually "it all depends".
In theory, it would be possible to recognise even the tiniest of differences as sufficient to delineate a separate species, provided only that the difference is clear and consistent (and that other criteria are met). There is no universal rule to state the smallest allowable difference between two species, but in general, very trivial differences are ignored on the twin grounds of simple practicality, and genetic similarity: if two population groups are so close that the distinction between them rests on an obscure and microscopic difference in morphology, or a single base substitution in a DNA sequence, then a demonstration of restricted gene flow between the populations will probably be difficult in any case.
More typically, one or other of the following requirements must be met:
Sometimes it is not possible to isolate a single difference between species, and several factors must be taken in combination. This is often the case with plants in particular. In eucalypts, for example, Corymbia ficifolia cannot be reliably distinguished from its close relative Corymbia calophylla by any single measure (and sometimes individual trees cannot be definitely assigned to either species), but populations of Corymbia can be clearly told apart by comparing the colour of flowers, bark, and buds, number of flowers for a given size of tree, and the shape of the leaves and fruit.
- It is possible to reliably measure a quantitative difference between the two groups that does not overlap. A population has, for example, thicker fur, rougher bark, longer ears, or larger seeds than another population, and although this characteristic may vary within each population, the two do not grade into one another, and given a reasonably large sample size, there is a definite discontinuity between them. Note that this applies to populations, not individual organisms, and that a small number of exceptional individuals within a population may 'break the rule' without invalidating it. The less a quantitative difference varies within a population and the more it varies between populations, the better the case for making a distinction. Nevertheless, borderline situations can only be resolved by making a 'best-guess' judgement.
- It is possible to distinguish a qualitative difference between the populations; a feature that does not vary continuously but is either entirely present or entirely absent. This might be a distinctively shaped seed pod, an extra primary feather, a particular courting behaviour, or a clearly different DNA sequence.
When using a combination of characteristics to distinguish between populations, it is necessary to use a reasonably small number of factors (if more than a handful are needed, the genetic difference between the populations is likely to be insignificant and is unlikely to endure into the future), and to choose factors that are functionally independent (height and weight, for example, should usually be considered as one factor, not two).
Historical development of the species concept
In the earliest works of science, a species was simply an individual organism that represented a group of similar or nearly identical organisms. No other relationships beyond that group were implied. When early observers began to develop systems of organization for living things, they began to place formerly isolated species into a context. To the modern mind, many of the schemes delineated are whimsical at best, such as those that determined consanguinity based on color (all plants with yellow flowers) or behavior (snakes, scorpions and certain biting ants).
In the 18th century Carolus Linnaeus classified organisms according to differences in the form of reproductive apparatus. Although his system of classification sorts organisms according to degrees of similarity, it made no claims about the relationship between similar species. At the time, it was common to believe that there is no organic connection between species, no matter how similar they appear; every species was individually created by God, a view today called creationism. This approach also suggested a type of idealism: the notion that each species exists as an "ideal form". Although there are always differences (although sometimes minute) between individual organisms, Linnaeus considered such variation problematic. He strove to identify individual organisms that were exemplary of the species, and considered other non-exemplary organisms to be deviant and imperfect.
By the 19th century most naturalists understood that species could change form over time, and that the history of the planet provided enough time for major changes. As such, the new emphasis was on determining how a species could change over time. Lamarck suggested that an organism could pass on an acquired trait to its offspring. As an example, imagine an animal that repeatedly stretches its neck in order to reach the treetops: the longer neck that it has acquired would then, according to this theory, be passed on to its offspring. This well-known and simplistic example, however, does not do justice to the breadth and subtly of Lamarck's ideas.
Lamarck's most important insight may have been that species can be extraordinarily fluid; his 1809 Zoological Philosophy contained one of the first logical refutations of creationism. With the advent of Darwin, Lamarck's reputation suffered gravely. It was not until the late 20th century that his work began to be reexamined, and took its place as a fundamental stepping stone to the modern theory of adaptive mutation. Lamarck's long-discarded ideas of the goal-oriented evolution of species, also known the teleological process, have also received renewed attention, particularly by proponents of artificial selection.
Charles Darwin and Alfred Wallace provided what scientists now consider the most powerful and compelling theory of evolution. Basically, Darwin argued that it is populations that evolve, not individuals. His argument relies on a radical shift in perspective from Linnaeus: rather than defining species in ideal terms (and searching for an ideal representative and rejecting deviations), Darwin considered variation among individuals to be natural. He further argued that such variation, far from being problematic, is actually a good thing.
Following Thomas Malthus, he suggested that population would often exceed the amount of food available, and that some organisms would die. Darwin suggested that those organisms that would die would be those less adapted to their environment, and that those that survived -- and reproduced -- would be those best adapted to their environment. Variation among members of a species is important because different and changing environments favor different traits (i.e. there is no ideal trait; whether a trait is beneficial or not depends on the environment).
These survivors would not pass acquired traits on to their offspring; they would pass their inherited traits on to their offspring. But since the environment effectively selected which organisms would live to reproduce, the environment would select which traits would be passed on. This is the theory of evolution by "natural selection." For example, among a group of animals some have longer necks, others have shorter necks. If all the leaves are high up, those with shorter necks will die; those with longer necks will thrive. This process is evident today as resistant strains of bacteria evolve.
The development of the field of genetics (many years after Darwin) has revealed the mechanisms that generate variation as well as those through which traits are passed on from generation to generation.
The theory of the evolution of species through natural selection has two important implications for discussions of species -- consequences that fundamentally challenge the assumptions behind Linnaeus' taxonomy. First, it suggests that species are not just similar, they may actually be related. Some students of Darwin argue that all species are descended from a common ancestor. Second, it supposes that "species" are not homogeneous, fixed, permanent things; members of a species are all different, and over time species change. This suggests that species do not have any clear boundaries but are rather momentary statistical effects of constantly changing gene-frequencies. One may still use Linnaeus' taxonomy to identify individual plants and animals, but one can no longer think of species as independent and immutable.
The rise of a new species from a parental line is called speciation. There is no clear line demarcating the ancestral species from the descendant species.
Although the current scientific understanding of species suggests there is no principled, black and white way to distinguish between different species in all cases, biologists continue to seek concrete ways to operationalize the idea. One of the most popular biological definitions of species is in terms of reproductive isolation; if two creatures cannot reproduce to produce fertile offspring, then they are in different species. This definition captures a number of intuitive species boundaries, but nonetheless has some problems, however. It has nothing to say about species that reproduce asexually, for example, and is it very difficult to apply to extinct species. Moreover, boundaries between species are often fuzzy: there are examples where members of one population can produce fertile offspring with a second population, and members of the second population can produce fertile offspring with members of a third population, but members of the first and third population cannot produces fertile offspring. Consequently, some people reject this notion of species.
Richard Dawkins defines two organisms as conspecific if and only if they have the same number of chromosomes and, for each chromosome, both organisms have the same number of nucleotides. (The Blind Watchmaker, p. 118)
The classification of species has been profoundly affected by technological advances that have allowed researchers to determine relatedness based on genetic markers. The results have been nothing short of revolutionary, resulting in the reordering of vast expanses of the phylogenetic tree (see also molecular phylogeny).
A species name can be:
There are several common species names. Most of these are adjectives.
- A noun in apposition with the genus: Panthera leo. The words agree in case but not necessarily in gender.
- An adjective, agreeing in case and gender with the genus: Allium sativum.
- A noun or adjective in the genitive. This is common in parasites: Xenos vesparum, Anaticola phoenicopteri. Also, names of people and places are used in the genitive: Latimeria chalumnae.
Linnaean taxonomy discusses how the category "species" meshes with other classification categories, such as "kingdom" and "genus".
Compare with race.
In chemistry, a species indicates that two particles are the same atomic nucleus, atom, molecule, or ion.
Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Species."
| The following table is compiled from various sources, across various languages. When English abbreviations or acronyms come from a non-English source, this is noted. | |||
| Entry | Source | Expression | Field |
| sp | English | Species | Biology & Biotechnology, Medicine |
Source: compiled by the editor, based on several corpora (additional references). | |||
Synonym: SpeciesSynonym: variety (n). (additional references) |
| Context | Synonyms within Context (source: adapted from Roget's Thesaurus). |
Class | Kind, sort, genus, species, variety, family, order, kingdom, race, tribe, caste, sept, clan, breed, type, subtype, kit, sect, set, subset; assortment; feather, kidney; suit; range; gender, sex, kin. |
Mankind | Noun: man, mankind; human race, human species, human kind, human nature; humanity, mortality, flesh, generation. |
| Source: adapted from Roget's Thesaurus. | |
| Domain | Usage | |
Screenplays | It came to me when I tried to classify your species. I realized that you're not actually mammals (The Matrix; writing credit: Andy Wachowski and Larry Wachowski.) You're an interesting species, an interesting mix. You're capable of such beautiful dreams and such horrible nightmares (Contact; writing credit: Carl Sagan;) Ellen Ripley died trying to wipe this species out. For all intents and purposes, she succeeded (Alien: Resurrection; writing credit: Dan O'Bannon; Ronald Shusett) Mankind, probably the most mysterious species on our planet (Lola rennt; writing credit: Tom Tykwer) Try a couple of species removed (Dinosaur; writing credit: Walon Green; Thom Enriquez) | |
Movie/TV Titles | Male of the Species (1969) Clay or the Origin of Species (1965) The Female of the Species (1916) A Species of Mexican Man (1915) The Female of the Species (1914) | |
Source: compiled by the editor from various references; see credits. | ||
| Domain | Title | ||
Books |
| ||
Periodicals |
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Theater & Movies | |||
Music |
| ||
Source: compiled by the editor from various references; see credits. | |||
| Thumbnail | Description & Credit | Thumbnail | Description & Credit |
 | Shows photo of Sarah Stewart. Ms. Stewart was the first to demonstrate virus causing cancer in many species. Credit: Unknown photographer/artist. |  | Shown are electron micrographs of the family of retroviruses that reproduce in t-lymphocytes. Retroviruses, which cause a variety of naturally occurring cancers in many animal species, also cause cancers in human beings. The first two human retroviruses to be discovered and characterized, human t-cell leukemia virus type I (HTLV-I) and type II (HTLV-II), have been associated with the human cancers known, respectively, as adult t-cell leukemia and hairy cell leukemia. HTLV-III is the AIDS virus, now called HIV-I. Epidemiologic studies have shown that HTLV-I infection and t-cell malignancy both cluster in certain geographic areas and in certain populations, and suggest that transmission occurs in the household, through sexual contacts, and perhaps at birth. See artwork: GR-30. Credit: Unknown photographer/artist. |
 | Streptococci are subdivided into groups based on what antibodies recognize their surface antigens. Group D contains five species, S. faecalis, S. faecium, S. durans, S. avium, and S. bovis. Credit: CDC. |  | Trichinosis, or trichinellosis, is caused by eating raw or undercooked pork infected with the larvae of a species of worm called Trichinella. Initial symptoms include nausea, diarrhea, vomiting, fatigue, fever, and abdominal discomfort. Credit: CDC. |
 | The Lena River, some 2,800 miles(4,500km) long, is one of the largest rivers in the world. The Lena Delta Reserve is the most extensive protected wilderness area in Russia. It is an important refuge and breeding grounds for many species of Siberian wildlife. Credit: NASA. |  | Hawaiian monk seal - Monachus schauinslandi. Tagging operations conducted under the auspices of the Bureau of Commercial Fisheries. Techniques were being developed at this time as this was only the second time that any Hawaiian Monk seals were tagged. Other than for needs of scientific studies, human interaction with protected species should be minimized. Credit: NOAA's Ark (Animals). |
 | Camp on eastern Lisianski Island Island was station for World Longitude Campaign Nesting place for albatross and other marine bird species Astro party of E. J. Brown. Credit: Coast & Geodetic Survey Historical Image Collection. |  | Mute swans in flight. Mute swans are an agressive invasive species. There are now over 3,000 mute swans in the Maryland portion of the Chesapeake Bay. They are easily distinguished from the tundra swan by their orange beaks. Credit: America's Coastlines. |
 | View from delta splay along Southwest Pass towards islands composed of Phragmites, an exotic species commonly called roseau cane. Credit: America's Coastlines. |  | Fisheries biologists sorting, counting, and measuring various species. Credit: Paths Less Taken - NOAA at the Ends of the Earth. |
Source: pictures compiled by the editor from various references; see picture credits. | |||
 |  |
| "VHS 1" by A. Carlos Herrera Commentary: "VHS Format, an endangered species." | "Honeysuckle" by Bobbie Osborne Commentary: "Honeysuckle (Lonicera) The honeysuckle family includes 180 species of shrubs and climbing vines that grow in varied habitats ranging from woodlands to rocky places. . All are known for their attractive, often fragrant, 1/2- to 1-inch pink, white or red" |
Source: photographs selected by the editor, with permission from the photographers. | |
| Author | Quotation |
Charles | At last gleams of light have come, and I am almost convinced that species are not (it is like confessing a murder) immutable. |
Charles Caleb Colton | To despise our own species is the price we must often pay for knowledge of it. |
Christian Nevell Bovee | Bad taste is a species of bad morals. |
Friedrich Nietzsche | Let us beware of saying that death is the opposite of life. The living being is only a species of the dead, and a very rare species. |
Georg C. Lichtenberg | A schoolteacher or professor cannot educate individuals, he educates only species. |
Samuel Taylor Coleridge | All truth is a species of revelation. |
| My case is a species of madness, only that it is a derangement of the Volition, and not of the intellectual faculties. | |
Seneca | However degraded or wretched a fellow mortal may be, he is still a member of our common species. |
William Godwin | The most desirable condition of the human species, is a state of society. |
Source: compiled by the editor from various references. | |
| Author | Date | Quotation |
John Locke | 1690 | Which being a trespass against the whole species, and the peace and safety of it, provided for by the law of nature, every man upon this score, by the right he hath to preserve mankind in general, may restrain, or where it is necessary, destroy things noxious to them, and so may bring such evil on any one, who hath transgressed that law, as may make him repent the doing of it, and thereby deter him, and by his example others, from doing the like mischief. (Second Treatise of Government) |
Source: compiled by the editor from various references. | ||
| Title | Author | Quote |
Last Chance To See | Douglas Adams | The great thing about being the only species that makes a distinction between right and wrong is that we can make up the rules for ourselves as we go along |
Les Miserables | Hugo, Victor | He saw, with disquietude, shaken within him that species of frightful calm which the injustice of his fate had given him. |
Gulliver's Travels | Swift, Jonathan | The assembly did therefore exhort him, either to employ me like the rest of my species, or command me to swim back to the place from where I came |
Walden | Thoreau, Henry David | It is now filled with the smooth sumach (Rhus glabra), and one of the earliest species of goldenrod (Solidago stricta) grows there luxuriantly |
Source: compiled by the editor from various references. | ||
| Subject | Topic | Quote |
Health | Rarely, other Candida species. (references) | |
Four species of Plasmodium infect humans. (references) | ||
The type species is chlamydia trachomatis. (references) | ||
Business | It is based on high market value species such as tuna, lobster, shrimp, sardine, and other fish species. (references) | |
Its fishing industry is based on high market value species such as tuna, lobster, shrimp, sardine, and other fish species. (references) | ||
Before any new seed species is allowed to be planted for commercial purposes in Germany, it needs to fulfill the standards of the Saatgutverkehrsgesetz. (references) | ||
Economic History | Spain | Demand is concentrated in one species, southern yellow pine. (references) |
Kazakhstan | Kazakhstan is a signatory to the Convention on International Trade in Endangered Species. (references) | |
Namibia | The main species found in abundance off Namibia are pilchards (sardines), anchovy, hake, and horse mackerel. (references) | |
Political Economy | MEXICO | Mexico passed a law in 1996 providing protection to plant species, and in 1998 provided protection for integrated circuits. (references) |
Trade | Argentina | Certain products of in danger species are prohibited from exporting. (references) |
Luxembourg | Among these limited items are endangered species, including those listed in the CITES convention. (references) | |
Lexicography | Devil's Dictionary | ADDER, n. A species of snake. So called from its habit of adding funeral outlays to the other expenses of living. |
Source: compiled by the editor from ICON Group International, Inc.; see credits. | ||
| Speaker | Term | Phrase(s) |
James Madison | 1809-1817 | To superadd a fresh motive to emigration by revoking the liberty which they now enjoy, would be the same species of folly which has dishonored and depopulated flourishing kingdoms. |
James Monroe | 1817-1825 | This country had, in fact, become the theater of every species of lawless adventure. |
Andrew Jackson | 1829-1837 | What ever other species of domestic industry, having the importance to which I have referred, may be expected, after temporary protection, to compete with foreign labor on equal terms merit the same attention in a subordinate degree. |
Calvin Coolidge | 1923-1929 | The collection of any taxes which are not absolutely required, which do not beyond reasonable doubt contribute to the public welfare, is only a species of legalized larceny. |
Source: compiled by the editor from various references. | ||
| "Species" is generally used as a noun (common) -- approximately 99.56% of the time. "Species" is used about 9,587 times out of a sample of 100 million words spoken or written in English. Its rank is based on over 700,000 words used in the English language. Some parts-of-speech are not covered due to the samples used by the British National Corpus. (note: percents less than one-hundredth of one percent have been omitted) |
| Parts of Speech | Percent | Usage per 100 Million Words | Rank in English |
| Noun (common) | 99.56% | 9,545 | 997 |
| Noun (plural) | 0.44% | 42 | 52,864 |
| Total | 100.00% | 9,587 | N/A |
Source: compiled by the editor from several corpora; see credits.
Expressions using "species": bacteria species ♦ bird species ♦ coniferous species ♦ definition by genus and species ♦ domesticated or cultivated species ♦ endangered species ♦ fluorinated species ♦ foreign to the species ♦ Incipient species ♦ infima species ♦ intercropped species ♦ light demanding species ♦ migratory species ♦ our species ♦ Reactive Oxygen Species ♦ reservoir species ♦ rich in species ♦ species of insect ♦ Species Specificity ♦ the species ♦ type species. Additional references. | |
| Hyphenated Usage | |
Beginning with "species": species-area, species-characteristic, species-diagnostic, species-identity, species-inherited, species-isolating, species-ist, species-lines, species-need, species-poor, species-rich, species-richness, species-specific, species-specificity, species--typical, species-wide. | |
Ending with "species": cross-species, multi-species, sub-species. | |
| Source: compiled by the editor from various references; see credits. | |
| The following statistics estimate the number of searches per day across the major English-language search engines as identified by various trade publications. Hyperlinks lead to commercial use of the expression at Amazon.com. |
| Expression | Frequency per Day | Expression | Frequency per Day |
endangered species | 1,993 | wood species | 42 |
fish species | 263 | cat species | 37 |
species | 222 | bee species | 37 |
endangered species list | 166 | elephant species two | 34 |
species spider | 122 | endangered species animal | 33 |
species tree | 117 | orchid species | 33 |
endangered species act | 113 | parrot species | 32 |
bird species | 103 | fish species tropical | 29 |
species turtle | 90 | monkey species | 29 |
origin of the species | 81 | endangered species store | 29 |
species movie | 70 | bee rare species | 28 |
snake species | 68 | endanger species | 26 |
invasive species | 59 | frog species | 26 |
endangered species picture | 58 | plant species | 25 |
dog species | 57 | butterfly species | 25 |
endangered species north america | 51 | new species | 24 |
ant species | 50 | endangered species of the rain forest | 24 |
extinct species | 49 | duck species | 24 |
species 2 | 47 | asia endangered species | 24 |
species of shark | 43 | animal species | 23 |
insect species | 23 | ||
| Source: compiled by the editor from various references; see credits. | |||
| Language | Translations for "species"; alternative meanings/domain in parentheses. | |
Albanian | spec (pepper), soj (family, kin, kind, persuasion, relative, shape, sort, stock, type), lloj (assortment, brand, brood, cast, class, description, form, genre, kidney, kind, nature, persuasion, race, rate, shape, sort, stamp, stock, style, type, variety), farë (egg, embryo, germ, pip, seed, semen, sort, spawn, sperm). (various references) | |
Arabic | نوع (brood, change, class, description, form, gender, genus, grain, kidney, kind, manner, order, quality, ripeness, run, sex, sort, stripe, style, type, variegate, variety, vary), صنف (article, assort, brand, categorize, category, class, classification, classify, compile, designate, digest, distinguish, distribute, grade, group, kind, label, pigeonhole, place, rank, rate, sort, stow, systematize, table, tabulate, type), صورة ذهنية (vista), خبز القربان المقدس (host). (various references) | |
Bulgarian | сорт (breed, class, degree, description, genus, grade, kind, nature, order, persuasion, rate, sort, strain, style, tap, variety), род (breed, clan, family, gender, genus, house, kin, kind, kindred, line, manner, name, order, origin, parentage, race, rod, sort, stamp, stock, strain, tribe), разновидност (diversity, kind, multiformity, multiplicity, variation, variety), вид (air, appearance, aspect, blush, breed, cast, clan, class, complexion, demeanor, demeanour, description, form, genre, genus, grade, guise, kidney, kind, likeness, look, manner, mien, mode, nature, order, persuasion, presence, race, shape, show, similitude, sort, strain, stripe, style, taxon, type, variety, view), порода (breed, kind, race, stock). (various references) | |
Chinese | 种类 (Varietal), 種類 (class, kind, sort). (various references) | |
Czech | rod (ancestry, clan, gender, generation, genus, kin, parentage, stock, tribe), odrùda (breed, variety), druh (companion, Comrade, description, fellow, genus, kind, mate, nature, peer, race, strain, style, type, variety, yokefellow, yokemate). ( |
