The species problem is the set of questions that arises when biologists attempt to define what a species is. Such a definition is called a species concept; there are at least 26 recognized species concepts. A species concept that works well for sexually reproducing organisms such as birds is useless for species that reproduce asexually, such as bacteria. The scientific study of the species problem has been called microtaxonomy.
One common, but sometimes difficult, question is how best to decide which species an organism belongs to, because reproductively isolated groups may not be readily recognizable, and cryptic species may be present. There is a continuum from reproductive isolation with no interbreeding, to panmixis, unlimited interbreeding. Populations can move forward or backwards along this continuum, at any point meeting the criteria for one or another species concept, and failing others.
The current meaning of the phrase "species problem" is quite different from what Charles Darwin and others meant by it during the 19th and early 20th centuries. For Darwin, the species problem was the question of how new species arose. Darwin was however one of the first people to question how well-defined species are, given that they constantly change.
The idea that an organism reproduces by giving birth to a similar organism, or producing seeds that grow to a similar organism, goes back to the earliest days of farming. While people tended to think of this as a relatively stable process, many thought that change was possible. The term species was just used as a term for a sort or kind of organism, until in 1686 John Ray introduced the biological concept that species were distinguished by always producing the same species, and this was fixed and permanent, though considerable variation was possible within a species. Carolus Linnaeus (1707–1778) formalized the taxonomic rank of species, and devised the two part naming system of binomial nomenclature that we use today. However, this did not prevent disagreements on the best way to identify species.
"The traditional view, which was developed by Cain, Mayr and Hull in the mid-twentieth century, claims that until the ‘Origin of species’ by Charles Darwin both philosophy and biology considered species as invariable natural kinds with essential features. This ‘essentialism story’ was adopted by many authors, but questioned from the beginning by a minority … when Aristotle and the early naturalists wrote about the essences of species, they meant essential ‘functions’, not essential ‘properties’. Richards pointed out [Richard A. Richards, The Species Problem: A Philosophical Analysis, Cambridge University Press, 2010] that Linnaeus saw species as eternally fixed in his very first publication from 1735, but only a few years later he discovered hybridization as a modus for speciation.
Charles Darwin's famous book On the Origin of Species (1859) offered an explanation as to how species evolve, given enough time. Although Darwin did not provide details on how species can split into two, he viewed speciation as a gradual process. If Darwin was correct, then, when new incipient species are forming, there must be a period of time when they are not yet distinct enough to be recognized as species. Darwin's theory suggested that there was often not going to be an objective fact of the matter, on whether there were one or two species.
Darwin's book triggered a crisis of uncertainty for some biologists over the objectivity of species, and some came to wonder whether individual species could be objectively real — i.e. have an existence that is independent of the human observer.
In the 1920s and 1930s, Mendel's theory of inheritance and Darwin's theory of evolution by natural selection were joined in what was called the modern synthesis. This conjunction of theories also had a large impact on how biologists think about species. Edward Poulton anticipated many ideas on species that today are well accepted, and that were later more fully developed by Theodosius Dobzhansky and Ernst Mayr, two of the architects of the modern synthesis. Dobzhansky's 1937 book articulated the genetic processes that occur when incipient species are beginning to diverge. In particular, Dobzhansky described the critical role, for the formation of new species, of the evolution of reproductive isolation.
Ernst Mayr's 1942 book was a turning point for the species problem. In it, he wrote about how different investigators approach species identification, and he characterized their approaches as species concepts. He argued for what came to be called the Biological Species Concept (BSC), that a species consists of populations of organisms that can reproduce with one another and that are reproductively isolated from other populations, though he was not the first to define "species" on the basis of reproductive compatibility. For example, Mayr discusses how Buffon proposed this kind of definition of "species" in 1753. Theodosius Dobzhansky was a contemporary of Mayr and the author of a classic book about the evolutionary origins of reproductive barriers between species, published a few years before Mayr's. Many biologists credit Dobzhansky and Mayr jointly for emphasizing reproductive isolation.
After Mayr's book, some two dozen species concepts were introduced. Some, such as the Phylogenetic Species Concept (PSC), were designed to be more useful than the BSC for describing species. Many authors have professed to "solve" or "dissolve" the species problem. Some have argued that the species problem is too multidimensional to be "solved" by any one concept. Since the 1990s, others have argued that concepts intended to help describe species have not helped to resolve the species problem. Although Mayr promoted the BSC for use in systematics, some systematists have criticized it as not operational. For others, the BSC is the preferred definition of species. Many geneticists who work on speciation prefer the BSC because it emphasizes the role of reproductive isolation. It has been argued that the BSC is a natural consequence of the effect of sexual reproduction on the dynamics of natural selection.
Realism, in the context of the species problem, is the philosophical position that species are real mind-independent entities, natural kinds. Mayr, a proponent of realism, attempted to demonstrate species exist as natural, extra-mental categories. He showed for example that the New Guinean tribesman classify 136 species of birds, which Western ornithologists came to independently recognize:
"I have always thought that there is no more devastating refutation of the nominalistic claims than the above mentioned fact that primitive natives in New Guinea, with a Stone Age culture, recognize as species exactly the same entities of nature as western taxonomists. If species were something purely arbitrary, it would be totally improbable for representatives of two drastically different cultures to arrive at the identical species delimitations."
Mayr's argument however has been criticized:
"The fact that independently observing humans see much the same species in nature does not show that species are real rather than nominal categories. The most it shows is that all human brains are wired up with a similar perceptual cluster statistic (Ridley, 1993). On this view we [humans] might have been ‘wired’ differently and different species might now be wired differently from us, so that no one wiring can be said to be ‘true’ or veridical."
Another position of realism is that natural kinds are demarcated by the world itself by having a unique property that is shared by all the members of a species, and none outside the group. In other words, a natural kind possesses an essential or intrinsic feature (“essence”) that is self-individuating and non-arbitrary. This notion has been heavily criticized as essentialist, but modern realists have argued that while biological natural kinds have essences, these need not be fixed and are prone to change through speciation. According to Mayr (1957) reproductive isolation or interbreeding "supplies an objective yardstick, a completely non-arbitrary criterion” and "describing a presence or absence relationship makes this species concept non-arbitrary". The BSC defines species as "groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups". From this perspective, each species is based on a property (reproductive isolation) that is shared by all the organisms in the species that objectively distinguishes them.
Some philosophical variants of nominalism propose that species are just names that people have assigned to groups of creatures but where the lines between species get drawn does not reflect any fundamental underlying biological cut-off point. In this view, the kinds of things that people have given names to, do not reflect any underlying reality. It then follows that species do not exist outside the mind, because species are just named abstractions. If species are not real, then it would not be sensible to talk about "the origin of a species" or the "evolution of a species". As recently at least as the 1950s, some authors adopted this view and wrote of species as not being real.
A counterpoint to the nominalist views in regard to species, was raised by Michael Ghiselin who argued that an individual species is not a type, but rather an actual individual, an actual entity. This idea comes from thinking of a species as an evolving dynamic population. If viewed as an entity, a species would exist regardless of whether or not people have observed it and whether or not it has been given a name.
A popular alternative view, pragmatism, espoused by philosophers such as Philip Kitcher and John Dupre states while species do not exist in the sense of natural kinds, they are conceptually real and exist for convenience and for practical applications. For example, regardless of which definition of species one uses, one can still quantitatively compare species diversity across regions or decades, as long as the definition is held constant within a study. This has practical importance in advancing biodiversity science and environmental science.
The nominalist critique of the view that kinds of things exist, raises for consideration the role that humans play in the species problem. For example, Haldane suggested that species are just mental abstractions.
Several authors have noted the similarity between "species", as a word of ambiguous meaning, and points made by Wittgenstein on family resemblance concepts and the indeterminacy of language.
Under the first view, species appear to us as typical natural kinds, but when biologists turn to understand species evolutionarily they are revealed as changeable and without sharp boundaries. Hey argued that it is unrealistic to expect that one definition of "species" is going to serve the need for categorization and still reflect the changeable realities of evolving species.
Many approaches to the species problem have attempted to develop one single common conception of what species are and of how they should be identified. It is thought that, if such a monistic description of species could be developed and agreed upon, then the species problem would be solved. In contrast, some authors have argued for pluralism, claiming that biologists cannot have just one shared concept of species, and that they should accept multiple, seemingly incompatible ideas about species. David Hull however argued that pluralist proposals were unlikely to actually solve the species problem.
"No term is more difficult to define than "species," and on no point are zoologists more divided than as to what should be understood by this word." Nicholson (1872).
"Of late, the futility of attempts to find a universally valid criterion for distinguishing species has come to be fairly generally, if reluctantly, recognized" Dobzhansky (1937).
"The concept of a species is a concession to our linguistic habits and neurological mechanisms" Haldane (1956).
"An important aspect of any species definition whether in neontology or palaeontology is that any statement that particular individuals (or fragmentary specimens) belong to a certain species is an hypothesis (not a fact)" Bonde (1977).
"The species problem is the long-standing failure of biologists to agree on how we should identify species and how we should define the word 'species'." Hey (2001).
"First, the species problem is not primarily an empirical one, but it is rather fraught with philosophical questions that require — but cannot be settled by — empirical evidence." Pigliucci (2003).
"We show that although discrete phenotypic clusters exist in most [plant] genera (> 80%), the correspondence of taxonomic species to these clusters is poor (< 60%) and no different between plants and animals. ... Contrary to conventional wisdom, plant species are more likely than animal species to represent reproductively independent lineages." Rieseberg et al. (2006).
In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to the focal taxon (which may be a species, family or in general any clade). It can therefore be considered an apomorphy in relation to a single taxon. The word autapomorphy, first introduced in 1950 by German entomologist Willi Hennig, is derived from the Greek words αὐτός, aut- = "self"; ἀπό, apo = "away from"; and μορφή, morphḗ = "shape".Bacterial taxonomy
Bacterial taxonomy is the taxonomy, i.e. the rank-based classification, of bacteria.
In the scientific classification established by Carl Linnaeus, each species has to be assigned to a genus (binary nomenclature), which in turn is a lower level of a hierarchy of ranks (family, suborder, order, subclass, class, division/phyla, kingdom and domain).
In the currently accepted classification of life, there are three domains (Eukaryotes, Bacteria and Archaea), which, in terms of taxonomy, despite following the same principles have several different conventions between them and between their subdivisions as are studied by different disciplines (botany, zoology, mycology and microbiology), for example in zoology there are type specimens, whereas in microbiology there are type strains.Clark's grebe
Clark's grebe (Aechmophorus clarkii) is a North American waterbird species in the grebe family. Until the 1980s, it was thought to be a pale morph of the western grebe, which it resembles in size, range, and behavior. Intermediates between the two species are known.
This species nests on large inland lakes in western North America and migrates to the Pacific coast over the winter. It maintains local populations year-round in California, Nevada, and Arizona (the Lower Colorado River Valley), as well as in central Mexico.
It feeds by diving for insects, polychaete worms, crustaceans, and salamanders.It performs the same elaborate courtship display as the western grebe.Edward Bagnall Poulton
Sir Edward Bagnall Poulton, FRS HFRSE FLS (27 January 1856 – 20 November 1943) was a British evolutionary biologist who was a lifelong advocate of natural selection through a period in which many scientists such as Reginald Punnett doubted its importance. He invented the term sympatric for evolution of species in the same place, and in his book The Colours of Animals (1890) was the first to recognise frequency-dependent selection.
Poulton is also remembered for his pioneering work on animal coloration. He is credited with inventing the term aposematism for warning coloration, as well as for his experiments on 'protective coloration' (camouflage).
Poulton became Hope Professor of Zoology at the University of Oxford in 1893.Ernst Mayr
Not to be confused with Ernst Mayr (computer scientist), Ernst Mayer, Ernst Meyer, Ernest Mayer or Ernest May.Ernst Walter Mayr (; 5 July 1904 – 3 February 2005) was one of the 20th century's leading evolutionary biologists. He was also a renowned taxonomist, tropical explorer, ornithologist, philosopher of biology, and historian of science. His work contributed to the conceptual revolution that led to the modern evolutionary synthesis of Mendelian genetics, systematics, and Darwinian evolution, and to the development of the biological species concept.
Although Charles Darwin and others posited that multiple species could evolve from a single common ancestor, the mechanism by which this occurred was not understood, creating the species problem. Ernst Mayr approached the problem with a new definition for species. In his book Systematics and the Origin of Species (1942) he wrote that a species is not just a group of morphologically similar individuals, but a group that can breed only among themselves, excluding all others. When populations within a species become isolated by geography, feeding strategy, mate choice, or other means, they may start to differ from other populations through genetic drift and natural selection, and over time may evolve into new species. The most significant and rapid genetic reorganization occurs in extremely small populations that have been isolated (as on islands).
His theory of peripatric speciation (a more precise form of allopatric speciation which he advanced), based on his work on birds, is still considered a leading mode of speciation, and was the theoretical underpinning for the theory of punctuated equilibrium, proposed by Niles Eldredge and Stephen Jay Gould. Mayr is sometimes credited with inventing modern philosophy of biology, particularly the part related to evolutionary biology, which he distinguished from physics due to its introduction of (natural) history into science.Glossary of speciation
This is a glossary of terms used in speciation research and related evolutionary disciplines. It is intended as introductory material and a structured organization of the often complex language used in the literature. Related glossaries in biology are: the glossary of biology, glossary of genetics, glossary of ecology, and the glossary of botany.James Mallet
James Mallet (born 15 March 1955 in London) is an evolutionary zoologist specialising in entomology.
He was educated at Winchester College.
He became professor of biological diversity at the Department of Biology, University College London. He was co-director of the Centre for Ecology and Evolution, a centre of excellence in research and teaching formed by University College London, the Institute of Zoology (Zoological Society of London), Natural History Museum, Imperial College, Queen Mary, Royal Holloway and Kew Gardens. In 2013 he was distinguished lecturer on Organismic and Evolutionary Biology at Harvard University. His research has included work on the species concept central to evolutionary biology, along with hybridization and the process of speciation.He was awarded the Darwin-Wallace Medal by the Linnean Society of London in 2008.Kevin de Queiroz
Kevin de Queiroz is a vertebrate, evolutionary, and systematic biologist. He has worked in the phylogenetics and evolutionary biology of squamate reptiles, the development of a unified species concept and of a phylogenetic approach to biological nomenclature, and the philosophy of systematic biology.Keystone species
A keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance. Such species are described as playing a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and numbers of various other species in the community. A keystone species is a plant or animal that plays a unique and crucial role in the way an ecosystem functions. Without keystone species, the ecosystem would be dramatically different or cease to exist altogether. Some keystone species, such as the wolf, are also apex predators.
The role that a keystone species plays in its ecosystem is analogous to the role of a keystone in an arch. While the keystone is under the least pressure of any of the stones in an arch, the arch still collapses without it. Similarly, an ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of biomass or productivity.
It became a popular concept in conservation biology, alongside flagship and umbrella species. Although the concept is valued as a descriptor for particularly strong inter-species interactions, and it has allowed easier communication between ecologists and conservation policy-makers, it has been criticized for oversimplifying complex ecological systems.Leigh Van Valen
Leigh Van Valen (August 12, 1935 – October 16, 2010) was a U.S. evolutionary biologist. At the time of his death, he was professor emeritus in the Department of Ecology and Evolution at the University of Chicago.
Amongst other work, Van Valen's proposed "Law of Extinction", known as Van Valen's law, drew upon the apparent constant probability (as opposed to rate) of extinction in families of related organisms, based on data compiled from existing literature on the duration of tens of thousands of genera throughout the fossil record. Van Valen proposed the Red Queen Hypothesis (1973), as an explanatory tangent to the Law of Extinction. The Red Queen Hypothesis captures the idea that there is a constant 'arms race' between co-evolving species. Its name is a reference to the Red Queen's race in Lewis Carroll's Through the Looking-Glass, in which the chess board moves such that Alice must continue running just to stay in the same place.Van Valen also defined the Ecological Species Concept in 1976, in contrast to Ernst Mayr's Biological Species Concept. In 1991, he proposed that HeLa cells be defined as a new species, which was named Helacyton gartleri.Van Valen originated the concept of fuzzy sets, prior to the formalization of this concept by L.A. Zadeh. He was the editor of the journal Evolutionary Theory, which he printed on simple paper stock under the motto, "Substance over form."
He had a deep understanding of many fields outside of biology, including measure theory, probability theory, logic, thermodynamics, epistemology and the philosophy of science. As a biologist, Van Valen considered the role of zoological and botanical gardens, in a world with a degrading natural environment, to be essential for the safeguard of endangered flora and fauna.Palawan bearded pig
The Palawan bearded pig (Sus ahoenobarbus) is a species of in the pig genus (Sus) endemic to the Philippines, where it can only be found on the archipelago of islands formed by Balabac, Palawan, and the Calamian Islands. They are 1 to 1.6 metres (3.3 to 5.2 ft) in length, about 1 metre (3.3 ft) tall and weigh up to 150 kilograms (330 lb).
Until recently, it was considered a subspecies of the Bornean bearded pig (Sus barbatus), but at least under the phylogenetic species concept, it must be classified as a separate species. For its treatment under other (and more widely used) species concepts, more study is required, but the presently available information seems to argue for full species status in any case.Paramo tapaculo
The Paramo tapaculo (Scytalopus opacus) is a species of bird in the Rhinocryptidae family. It is found at altitudes of 2,600 to 4,000 metres (8,500 to 13,100 ft) in the Andes of northern Peru, Ecuador and southern Colombia (Cordillera Central). It has traditionally been treated as a subspecies of S. canus, but the two have different voices, leading to them being split into separate species in 2010.
The Paramo tapaculo resembles other Scytalopus tapaculos, being overall dark grey with brown to the lower flanks. Females are dull brown above. The subspecies androstictus was described in 2010 from south-eastern Ecuador and northern Peru. Unlike the nominate subspecies, most male androstictus have white to the primary coverts. If following the phylogenetic species concept, androstictus would be a separate species, but under the biological species concept it "only" qualifies as a subspecies.
As the Paramo tapaculo generally is common to fairly common and occurs in several protected areas, it is unlikely to be threatened.Pseudoextinction
Pseudoextinction (or phyletic extinction) of a species occurs when all members of the species are extinct, but members of a daughter species remain alive. The term pseudoextinction refers to the evolution of a species into a new form, with the resultant disappearance of the ancestral form. Pseudoextinction results in the relationship between ancestor and descendant still existing even though the ancestor species no longer exists.The classic example is that of the non-avian dinosaurs. While the non-avian dinosaurs of the Mesozoic died out, their descendants, birds, live on today. As of now it is accepted that modern birds evolved from Archaeopteryx, a small dinosaur with flight feathers from the Mesozoic period. Many other families of bird-like dinosaurs also died out as the heirs of the dinosaurs continued to evolve, but because their birds continue to thrive in the world today their ancestors are only pseudoextinct.Robert Paine
Robert Paine may refer to:
Robert Treat Paine (1731–1814), signer of the United States Declaration of Independence
Robert Treat Paine, Jr. (1773–1811), poet and son of the signer
Robert Treat Paine (North Carolina) (1812–1872), U.S. Congressman from North Carolina
Robert Treat Paine (philanthropist) (1835–1910), Boston lawyer and philanthropist, great-grandson of the signer
Robert Paine (anthropologist) (1926-2010), English-born Canadian known for his studies of the Sami people
Robert T. Paine (zoologist) (1933–2016), American ecologist, who introduced the keystone species concept
Robert Paine (sculptor) (1870–1946), American artistRobert T. Paine (zoologist)
Robert Treat "Bob" Paine III (April 13, 1933 – June 13, 2016) was an American ecologist, who spent most of his career at the University of Washington. Paine coined the keystone species concept to explain the relationship between Pisaster ochraceus, a species of starfish, and Mytilus californianus, a species of mussel.Species
In biology, a species ( (listen)) is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined.
All species (except viruses) are given a two-part name, a "binomial". The first part of a binomial is the genus to which the species belongs. The second part is called the specific name or the specific epithet (in botanical nomenclature, also sometimes in zoological nomenclature). For example, Boa constrictor is one of four species of the genus Boa.
While the definitions given above may seem adequate, when looked at more closely they represent problematic species concepts. For example, the boundaries between closely related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, and in a ring species. Also, among organisms that reproduce only asexually, the concept of a reproductive species breaks down, and each clone is potentially a microspecies. Though none of these are entirely satisfactory definitions, scientists and conservationists need a species definition which allows them to work, regardless of the theoretical difficulties. If species were fixed and clearly distinct from one another, there would be no problem, but evolutionary processes cause species to change continually, and to grade into one another.
Species were seen from the time of Aristotle until the 18th century as fixed categories that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped that species could evolve given sufficient time. Charles Darwin's 1859 book The Origin of Species explained how species could arise by natural selection. That understanding was greatly extended in the 20th century through genetics and population ecology. Genetic variability arises from mutations and recombination, while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures. Genes can sometimes be exchanged between species by horizontal gene transfer; new species can arise rapidly through hybridisation and polyploidy; and species may become extinct for a variety of reasons. Viruses are a special case, driven by a balance of mutation and selection, and can be treated as quasispecies.Systematics and the Origin of Species
Systematics and the Origin of Species from the Viewpoint of a Zoologist is a book written by zoologist and evolutionary biologist Ernst Mayr, first published in 1942 by Columbia University Press. The book became one of the canonical publications on the modern synthesis.
Based on Mayr's Jesup Lectures delivered at Columbia University in 1941, the book combines concepts of zoology and genetics, and features Mayr's biological species concept. The biological species concept defines a species in terms of biological factors such as reproduction, taking into account ecology, geography, and life history; it remains an important and useful idea in biology, particularly for animal speciation.
In December 2004 the National Academy of Sciences held a colloquium in honour of Mayr's 100th birthday. Systematics and the Origin of Species: On Ernst Mayr's 100th Anniversary was also published in commemoration.Wheat leaf rust
Wheat leaf rust is a fungal disease that affects wheat, barley and rye stems, leaves and grains. In temperate zones it is destructive on winter wheat because the pathogen overwinters. Infections can lead up to 20% yield loss, which is exacerbated by dying leaves, which fertilize the fungus. The pathogen is Puccinia rust fungus. Puccinia triticina causes "black rust", P. recondita causes "brown rust", and P. striiformis causes "yellow rust". It is the most prevalent of all the wheat rust diseases, occurring in most wheat growing regions. It causes serious epidemics in North America, Mexico and South America and is a devastating seasonal disease in India. All three types of Puccinia are heteroecious requiring two distinct and distantly related hosts (alternate hosts). Rust and the similar smut are members of the class Pucciniomycetes but rust is not normally a black powdery mass.Yellow-striped chevrotain
The yellow-striped chevrotain (Moschiola kathygre) is a species of chevrotain described in 2005. It is found in the wet zones of Sri Lanka. It was recognized as a species distinct from Moschiola meminna based on the phylogenetic species concept.