The species , also species or species (often abbreviated to spec. , From Latin species 'type'), is the basic unit of biological systematics in biology (including virology ) . Every biological species ( species ) is a result of speciation . So far there has been no general definition of the “species” that equally meets the theoretical and practical requirements of all biological sub-disciplines. Rather, there are different species concepts in biology that lead to different classifications. Historically as well as currently, two approaches to species concepts play an important role:
- based on an assumed reproductive community (biological species definition)
- on the basis of the assumption of a group of individuals with characteristic common species characteristics, with the help of which the membership of a species should be clearly delimited, and which are determined on the basis of external ( morphological species concept) "or" hereditary characteristics.
With the emergence of cladistics , the chronologically defined phylogenetic species concept based on the biological concept of species has been added since the 1950s, according to which a species begins with species splitting , i.e. the formation of two species from one original species, and with their renewed species splitting or their extinction ends.
The problem of species definition consists of two sub-problems:
- Group formation: which individuals belong together?
- Ranking: Which of the numerous nested groups of graded similarities and relationships do we want to call "kind"?
Species as a taxon
A species as a taxon is a form of living being formally described and named according to the rules of taxonomy and biological nomenclature . A taxonomic species represents a scientific hypothesis and can be independent of a species concept, provided that one at least accepts that species are real and individual phenomena of nature. The species is a rank of the classic taxonomy that goes back to Carl von Linné . Some systematists who work purely on the basis of characteristics are of the opinion that species are more or less arbitrarily composed, artificial groups, only the individuals are ultimately real: Some go so far that, in their opinion, the concept of species, like all other ranks, should better be abolished. Most biologists are of the opinion that species are natural entities with real existence; there would then be species criteria by which real species could be identified. This notion is ultimately based on a distinction between units characterized by gene flow or horizontal gene transfer below the species level and the species for which this does not apply (lineages). For many biologists, including supporters of a phylogenetic species concept (see below), they are even the only natural taxonomic units in this sense.
According to the binary nomenclature introduced by Carl von Linné in 1753, the scientific name of a species (often of Latin or Greek origin) consists of two parts, both of which are written in italics. The first part of this name is the capitalized generic name . The second part is always written in lower case and in botany and prokaryotes referred to as an epithet ("specific epithet"), in zoology as a species name or species addition ("specific name"). In order to avoid confusion between the additional species and the entire species name, i.e. the binomial of the generic name and the additional species, the unambiguous English terms are either used or added in zoology, or terms such as "epithetum specificum" or "epitheton specificum" are used occasionally and informally .
- In the common beech ( Fagus sylvatica ) the part of the name Fagus denotes the genus, sylvatica is the specific epithet.
- With the lion ( Panthera leo ) the name part Panthera describes the genus, leo is the species name ("specific name").
Both in botany ( Code Article 46) and in zoology ( Code Article 51) it is recommended to add the names of the authors who have described the species to the scientific species name , at least when it comes to taxonomic or nomenclature questions. This is important, for example, to recognize homonyms , which are cases in which two authors have accidentally named two different species with the same name. Within the scope of the International Code of Nomenclature for Algae, Mushrooms and Plants , it is recommended to abbreviate the author's names, usually using the Brummit and Powell list of names as a basis (see article author abbreviations for botanists and mycologists ), for example "L." for Linnaeus.
- Example: Shiitake Lentinula edodes (Berk.) Pegler - Explanation: Miles Josef Berkeley first described the species, David Norman Pegler assigned it to today's system.
According to the International Rules for Zoological Nomenclature , the author (s) and the year of publication should be added to the species name at least once in every scientific text (Code Recommendation 51a). If two authors with the same surname were active in the relevant subject area, the abbreviated first name should be added to ensure clarity. If the species is now placed in a genus other than the one in which it was originally described, the author (s) and year must be put in brackets (Code Article 51.3). A comma is usually placed between the author and the year.
- Example: Lion Panthera leo (Linnaeus, 1758) - Explanation: Carl Nilsson Linnæus first described the big cat as Felis leo . Who first put it in the genus Panthera Oken, which is mostly used for lions today , is not relevant in zoology. Instead of Linnæus, Linnaeus is written because the author should be given in Latin letters (Code Recommendation 51 b).
The philosophers of antiquity did not yet know any systematic concepts and thus no concept of species in the modern sense. From Aristotle writings as the first philosopher known in which separate two - generally philosophically to understand - terms είδος ( eidos , the German translated "Art") and γένος ( genos , German "genus") are defining one another. In his categories he uses an example from the world of living beings to characterize them as second beings (δεύτεραι ουσίαι ) that are present in the individual. So there is a single human being in the human species and a single horse in the horse species, but both belong to the species of the living (ζῷον zoon ).
In his Historia animalium (Περί τα ζώα ιστοριών) Aristotle applies the terms είδος and γένος to the animal kingdom, but without establishing a taxonomic order. Rather, he speaks of the overlap of characteristics of the animal species (ἐπάλλαξις epállaxis ) and the need to define a single species on the basis of several secondary characteristics. Nevertheless, when describing the species, he deals with individual characteristic features. The term είδος is not consistently used in the sense of a modern species term as the lowest category between the individual living being and γένος, rather the meaning can usually best be given as “form”, “shape” or “ essence ”, while animal species are usually be referred to as γένος.
According to biblical Creation story in Genesis 1 created God between the 3rd and 6th day of creation, the plants and animals, "one any (each) according to their kinds" (ten times quote "after their kind" Genesis 1.11 to 27 LUT , to be understood as “ essence ”, Hebrew min מין or למינה, Genesis 1,11-27 OT ). In the Septuagint מין is translated with γένος (κατὰ γένος “according to / according to the type”, Genesis 1,11-27 LXX ), in the Vulgate, however, inconsistently, sometimes with genus and sometimes with species , whereby the prepositions also change ( secundum speciem suam, secundum suas species, species in suas, juxta genus suum, secundum genus suum, in genere suo , Genesis 1.11 to 27 VUL ). A statement is also made here about the reproduction of plants and animals "according to their kind", as God speaks in Genesis 1,11 LUT : "Let the earth grow up, grass and herbs that bring seeds, and fruitful trees on earth that each bear fruit according to his kind, in which their seed is ", as well as in Genesis 1,22 LUT on the animals of water and air:" Be fruitful and multiply. "
These biblical statements as well as Aristotle were formative for the ideas of the scholars of the West up to the modern age. In 1916, Pierre Duhem introduced the concept of essentialism for the philosophical conception of the essence or “essence” of an individual . According to Ernst Mayr , the belief in creation and the conception of an “unchangeable essence” ( είδος as being ), which ultimately went back to Plato , went well together and formed the basis for an “essentialist concept of species” as it dominated from the Middle Ages to the 19th century . According to this, all objects which have the same essence in common belong to the same kind. According to Mayr, "[d] er essentialism with its emphasis on discontinuity, constancy and typical values (typology)" was the background for typological species concepts, according to which an individual is always clearly of a certain one based on his - usually morphological - characteristics (type) Kind of heard.
This can also be seen in John Ray , who in 1686 in his Historia plantarum generalis defined the species of plants as reproductive communities with permanent species characteristics , after he had “long” searched for signs of their differentiation: “But none [no sign] seemed more reliable to us as separate propagation from the seed. Whatever differences arise in the individual or in the plant species from the seed of the same, they are accidental and not characteristic of the species. [...] Because those who differ in their species keep their species constantly, and none of them arise from the seeds of the other or vice versa. "
Systematisation by Carl von Linné
With Species Plantarum (1753) and Systema Naturae (1758), Carl von Linné was the first to set up an encaptic system of nature based on hierarchical categories ( class , order , genus , species and variety , but not yet family ) the species introduced the binary nomenclature from generic names and species epithet . Hierarchical means that the units are combined into groups at different levels, with the higher groups in the hierarchy being combined by general characteristics, the lower groups by increasingly specific characteristics (a certain individual belongs to a species, a genus, according to its combination of characteristics, a family, etc.). Encaptic means that the groups that are lower in the hierarchy are nested in exactly one group of the higher hierarchy level, for example each species in one and exactly one genus. In his Philosophia botanica he formulates: “There are so many ways in which the infinite being created in the beginning, so many different forms ; these forms, according to the introduced laws of reproduction, produced many [further forms], but always similar. ”In addition, he describes the species and the genus as the work of nature, the variety as the work of man, and order and class as dated Man-made unity. " The species are immutable , for their reproduction is true persistence."
While Georges-Louis Leclerc de Buffon still denied in 1749 that there were any categories in nature, he later revised this view for the species and formulated a typological concept of species with a constancy of species : “The imprint of each species is a type, its essential Characteristics are imprinted in unchangeable and constant traits, but all secondary characteristics vary: no individual is completely alike. "
Jean-Baptiste de Lamarck , on the other hand , who already assumes a transformation of species , regards species and all other categories as artificial. In 1809 he expressed himself in his Philosophy zoologique : "Nature did not really develop classes, orders, families, genera, permanent species, but only individuals." However, this does not prevent him from being very productive in the field of taxonomy Categories he knows how to use in practice.
Charles Darwin , who even on the nature of the title of his fundamental work On the Origin of Species ( On the Origin of Species speaks) of 1859, is afraid of a formulation of a Artbegriffs. According to Ernst Mayr , one can conclude from his notebooks from the 1830s that he had the idea of a species as a reproductive community at the time. In his Origin of Species , however, he unmistakably describes the terms species and variety as artificial: “These remarks show that I consider the term“ species ”to be arbitrary and, for the sake of convenience, applied to a number of very similar individuals and that it is not essentially different from the art expression “variety”, which is applied to less divergent and even more fluctuating forms. Likewise, the term "variety" is used only arbitrarily and for convenience in comparison to mere individual differences. "
Alfred Russel Wallace made a similar statement in 1856 in his basic work on the knightly butterflies (Papilionidae) in the Malay Archipelago , in which he explained various courses of evolution through natural selection . He describes species as "only strongly characterized races or local forms" and also goes into the fact that individuals of different species are generally regarded as incapable of producing fertile common offspring, but it is not even possible in one out of a thousand cases to have one Check mixing.
Since Darwin, the level of the species is no longer particularly distinguished compared to distinguishable subordinate (local populations) or superordinate (species groups or higher taxa). Within the taxonomy, species delimitation was subject to fashions and personal preferences, there are taxonomists who want to classify any distinguishable form as possible (“ splitter ”), and others who prefer broad species with numerous local races and populations (“ lumper ”).
At the end of the 19th century, biological species concepts of a reproductive community were discussed. In this sense, Erwin Stresemann expressed clear ideas about speciation and genetic isolation as early as 1919 in an article about European tree creepers : “The name only wants to express the fact that the [in the course of geographical separation] rose to the rank of species Have forms so far apart from one another physiologically that, as nature proves, they can come together again without intermingling. "
The biological species concepts of the reproductive community with Theodosius Dobzhansky and Ernst Mayr have dominated the scientific discourse since the second half of the 20th century. Dobzhansky links the concept of species - similarly to Stresemann - with speciation and in 1939 defines species as the "stage of the evolutionary process [...] in which groups of forms that have previously been able to reproduce with one another or at least were able to do so are divided into two or more separate groups, which cannot reproduce with one another for physiological reasons ”, while Mayr formulated in 1942:“ Species are groups of natural populations that actually or potentially multiply among one another and are reproducibly separated from other such groups. ”In an expanded biological species term, Mayr 2002 refers to the ecological niche in the definition of the term: "A species is a reproductive community of (reproductive-wise isolated from other) populations that occupies a specific niche in nature." Mayr defines the meaning of the species in biology as a natural "unit of evolution, the Systematics, ecology and nd of ethology ”and here sets it apart from all other systematic categories.
For practical reasons, typological species concepts also survive to this day. As before, the person referred to as the authority who is the first to publish the species description of a new species (species nova) names it on the basis of the characteristics of the type specimen with a self-selected species name from the genus name and the species epithet.
Debate about essentialism in the history of biology
According to Ernst Mayr, the history of the concept of species in biology begins with Carl von Linné . In his work on the history of science, he emphasizes that essentialism has dominated Western thinking to an extent that has not yet been fully appreciated, and equates typological with essentialist species concepts. In contrast, Mary Winsor emphasizes that the use of type species as prototypes for higher categories is incompatible with essentialism, and John S. Wilkins emphasizes that the typology of biologists and essentialism - which Winsor called the “method of specimens” - by no means are inevitably linked. While essences are definable and are common to all members of a species, types can be instantiated and are variable.
Morphological species concept
Typologically defined species are groups of organisms that are usually differentiated according to morphological characteristics (morphological species concept). However, other features, such as behavior, can also be used in an analogous manner. A species defined according to morphological criteria is called a morpho species .
- Horse and donkey can be clearly distinguished from one another morphologically and thus belong to different morpho species.
Lion and tiger can be clearly distinguished from each other morphologically and in behavior:
- Tigers are striped and live as solitary animals that only meet during the mating season.
- Lions only sometimes have a spotted pattern as young animals, they are not striped, the males have a more or less developed mane. Lions usually live in packs of females with their cubs, and one or more adult males.
- The fur characteristics and behavior of the species do not overlap in their expression, and if ( ligers and tigons in zoos) these intermediate forms are much rarer. Both are therefore easily separable morpho species (or ethos species ).
As a rule, only the morphological species concept can be used in paleontology . Since the number of finds is often limited, species delimitation in paleontology is particularly subjective . Example: The fossils found by two individuals in the same layer, i.e. living practically at the same time, differ greatly from one another:
- They can now be assigned to two different types if one is of the opinion that they differ far enough from a morphological type. But they can also be assigned to the same species if one is of the opinion that a greater range of variation, including the finds, can be assumed in this species.
- However, the differences can also be due to a clear sexual dimorphism (differences in the appearance of males and females) within a species.
These problems diminish with an increasing number of finds and thus with knowledge of the actual range of variation, but cannot be completely eliminated.
The morphological species concept is often used in ecology, botany and zoology. In other areas, such as in microbiology or in sub-areas of zoology, such as with nematodes , attempts at purely morphological species classification largely fail.
Problems of morphological delimitation
- Nature is not a rigid system, but is in constant change. Under the influence of various evolutionary factors , populations change gradually , occasionally also suddenly from generation to generation. An immutable type is therefore incompatible with the findings of evolutionary biology . There are no types or essences in living nature ( Ernst Mayr 1998).
- A categorization based on morphological characteristics cannot be objectified. A classification based on mere distinctness always depends on how exactly one examines the various individuals or populations and on which criteria the “difference” is determined, which leaves a lot of space for arbitrariness and interpretation. The more precise the investigation methods, the more noticeable differences between different individuals and populations become. As a consequence, every intraspecific variation, no matter how small, would be declared to be a separate taxon if the respective taxonomist considers the difference to be essential . The existence of hybrid and transitional forms further exacerbates the problem, because a clear, non-arbitrary demarcation according to morphological aspects is hardly possible here.
- The morphological concept of species cannot be followed consistently because it often contradicts observable biological reality. In practice this limitation arises u. a. from the existence of intraspecific polymorphisms . A number of species go through different stages during their individual development (e.g. larva → fly, caterpillar → butterfly) in which the respective phenotype is subject to drastic changes. Sexual dimorphisms are often encountered, species in which male and female individuals develop different phenotypes. For example, Linnaeus originally assigned males and females of the mallard to two different species; when the error was recognized, both were grouped into one species, although their differences had not changed.
- Many species are characterized by high phenotypic plasticity . A phenotype is not completely determined by the genotype , but rather the result of the interaction between genotype and environment. Depending on the environmental and living conditions, the same genotype can produce different site forms, which are assigned to different taxa according to morphological criteria, although they can be genetically completely identical (e.g. in the case of offshoots ). For example, the shape of the leaves of the dandelion varies greatly depending on the amount of rainfall, solar radiation and the time of year when the leaves are formed.
- There is also the opposite situation: biologically completely different species can converge in their phenotype due to similar selection conditions, so that they can no longer be easily distinguished from the outside, so-called twin species . The same problem arises with the cryptic species .
- Finally, a purely morphological delimitation criterion turned out to be not reliable enough, because the variations within a reproductive community can be greater than those between morphologically similar, i.e. populations of the same “type”, which however do not form a reproductive community.
Physiological species concept in bacteria
Bacteria show only a few morphological distinguishing features and have practically no recombination barriers . That is why the metabolism is used as a criterion to differentiate between strains. Because there is no generally accepted species criterion, bacterial strains represent the currently used basis for differentiation. The higher bacterial taxa are differentiated on the basis of biochemical characteristics such as the substance of the cell wall.
One tests on bacterial pure cultures to their "species determination" their ability to certain biochemical performances, such as the ability to break down certain "substrates", e. B. rarer types of sugar. This ability can be recognized very easily if the reaction product can change the color of a color indicator added to the culture medium. By inoculating a pure bacterial culture in a row of culture glasses with nutrient solutions, each of which only contains a certain substrate (“selective media”), a so-called “colorful row” is obtained, from whose color changes the type of bacteria can be determined according to a table. For this purpose, semi-automatic devices (“microplate readers”) were developed.
Since appropriate techniques have been available ( PCR ), bacterial strains have also been identified or differentiated on the basis of the DNA sequences. A widely accepted measure is that strains that have less than 70% of their genome in common should be considered separate species. Another measure is based on the similarity of the 16S rRNA genes. According to DNA analyzes, for example, less than 1% of the strains found in natural media could be reproduced on conventional nutrient media. In this way, up to 100,000 different bacterial genomes are said to have been found in one ml of soil, which were interpreted as different species. This should not be confused with the total number of germs , which is of the same order of magnitude, but only includes "a few" species that show up through the formation of colonies with a certain culture method.
Many differentiating criteria are purely pragmatic. At which level of distinction one understands tribes as species or even genera is a matter of convention. The physiological or genetic species delimitation in bacteria corresponds methodically to the typological species concept. Ernst Mayr, a passionate supporter of the biological species concept, therefore means: "Bacteria have no species".
Daniel Dykhuizen draws attention to the fact that - contrary to some beliefs - transformations, transductions and conjugations (as ways of exchanging DNA between strains) do not take place randomly, but preferentially between certain forms and virtually never between others. Accordingly, it would in principle be possible to develop a species concept for bacteria corresponding to the biological species concept in eukaryotes. Frederick M. Cohan , on the other hand, tries to develop a species concept based on ecotypes.
Biological or population genetic species concept
Towards the end of the 19th and beginning of the 20th century, population thinking gradually began to prevail in biology , which had consequences for the concept of species. Because typological classification schemes were unable or insufficiently able to depict the real conditions in nature, the biological system had to develop a new concept of species that was not based on abstract differences or subjective assessments of individual scientists, but on objectively ascertainable criteria. This definition is called a biological species definition , “It is called“ biological ”not because it has to do with biological taxa, but because its definition is biological. It uses criteria in terms of the inanimate world, are meaningless. " A biologically defined type is as biospecies referred.
The new term was based on two observations: on the one hand, species are composed of populations and, on the other hand, there are biological barriers to reproduction between populations of different species. “The [biological] species has two properties that make it fundamentally different from all other taxonomic categories, such as gender . First, it allows for a non-arbitrary definition - one could even go so far as to call it "self-operational" - by emphasizing the criterion of reproductive isolation from other populations. Second, the species is not defined, like all other categories, on the basis of its inherent properties, not on the basis of the possession of certain visible attributes, but through its relation to other species. ” This has - at least according to the majority of interpretations - the consequence that species are not classes, but individuals.
The criterion of reproductive capacity forms the core of the biological concept of species or of the biospecies. A biospecies is a group of actually or potentially reproducing individuals that produce fully fertile offspring:
- A species is a group of natural populations that can interbreed and are reproductively isolated from other groups .
The isolation mechanisms between the individual species should be of a biological nature, i.e. not based on external conditions, spatial or temporal separation, but rather be properties of the living beings themselves:
- Isolation mechanisms are biological properties of individual living beings that prevent populations of different sympatric species from crossing .
The cohesion of the biospecies, their genetic cohesion, is ensured by physiological, ethological , morphological and genetic properties that have an isolating effect on alien individuals. Since the isolation mechanisms prevent significant inter-species hybridization from occurring, members of a species form a reproductive community; between them there is gene flow, they share a gene pool and thus form a unit in which evolutionary change takes place.
- Horse and donkey can be crossed ( mule , mule ), but due to a genetic barrier they do not have any fertile offspring and thus form different biospecies.
- Lions and tigers can be crossed under artificial conditions ( zoo ) ( big cat hybrids : Liger Tigon ) and in the zoo they may have fertile offspring. In nature, they sometimes live in common areas of distribution, but natural hybrids have not yet been detected, which suggests that they do not mate. They are considered to be different bio-species due to ethological barriers.
- Geographically clearly separated populations are, since they cannot cross in nature, difficult to grasp according to the biological species concept. According to the theory of allopatric speciation , they are quasi “species in the process of creation”. There is actually no fundamental difficulty, since the question can be decided experimentally (if no biological isolation mechanisms have evolved, it is still the same type).
- The original version of the biological species concept does not contain a concept of time. Evidently only organisms living at the same time can cross with each other. This does not give a criterion as to whether organisms that had previously lived are to be counted as belonging to the same species or not. Later extensions of the concept (first probably Simpson 1951) attempted to overcome this by referring to evolutionarily definable units.
- Species that reproduce asexually are not included in the definition of the biological species concept. They are known as the agamo species . These include some protists , some fungi , some plants, such as the cultivated form of the banana (see also Genet ), as well as some animals (with parthenogenetic reproduction). Agamospecies also have no gene pool and are therefore not species according to the population-genetic species concept.
- Many animal and plant species interbreed with each other in nature ( introgression ), such as different hard coral species or whitebeam trees as well as different species from the viviparous toothcarp family, each within a genus, such as platy and swordtail in the genus Xiphophorus . Orchids can sometimes even breed fruitfully across genus boundaries. These hybrids are in the minority in nature, the various morphologically described orchid species therefore remain distinguishable according to the morphological species concept. According to the biological species concept, there are separate species if isolation mechanisms have developed that normally prevent hybridization, even if it were physiologically possible, e.g. B. climate-related differences in animals in the reproduction period or in plants in the flowering period. These mechanisms can collapse (e.g. through human intervention or drastic changes in the environment through climate change). In this way, according to the concept, previously separated species become one species again (e.g. observed in some orchid species in Central Europe). The same process can take place naturally (introgressive hybridization).
The biological species concept is often used in ecology, botany and zoology, especially in evolutionary biology . In a sense, it forms the standard model from which the other modern species concepts are derived or against which they are primarily differentiated. The necessary characters (lack of natural hybrids or common gene pool) are sometimes difficult to check; in certain areas, such as in palaeontology , biological or population-genetic species delimitations largely fail.
Phylogenetic or evolutionary species concept
- when all individuals of this species die out without leaving any offspring or
- when two new species arise from this species through species splitting.
Phylogenetic anagenesis is the change of a species in the period between two species divisions, i.e. during its existence. As long as there is no division, all individuals belong to the same species, even if they are morphologically distinguishable under certain circumstances.
The phylogenetic species concept is based on the phylogenetic systematics or " cladistics " and only has meaning in connection with this. In the context of the concept, species are objective, actually existing biological units. All higher units of the system are called "clades" according to the system and are (as monophyletic communities of organisms) in principle different from species. Due to the forked (dichotomous) division, all hierarchical units above the species (genus, family, etc.) have no meaning, but are only conventional aids to denote communities of descent of a certain level. The essential difference lies less in the consideration of the species than in that of these higher units. According to the phylogenetic species concept, clades can overlap if they are of hybridogenic origin.
- Each species and each species split in this model must first be defined, following the typological or biological species concept. The difficulties already discussed with the respective species concept can arise. The phylogenetic species concept only simplifies the consideration between two species splits by combining all populations of this period into one species. Ernst Mayr therefore means: "There are only two Art-Concepts, everything else are definitions" (see under "Quotations").
In addition, there are the following difficulties:
- A monophyletic community of descent is not necessarily recognizable. The lack of evidence of morphological and genetic differences cannot rule out a split that has already taken place.
- Phylogenetic bifurcations are often not symmetrical and are sometimes without genetic or morphological consequences in one of the two split-off lines. The species boundaries of the phylogenetic species concept can therefore hardly be traced back at certain times to separate fertile crossing and morphologically uniform populations. When a small group of a species is shipped from a continent to an island and there z. For example, due to strong selection, rapid speciation sets in - why should the creatures of the original species that have remained on the continent and which may not or cannot be detected change become a new species?
- The evolution of many taxa is reticulate, i.e. networked, and not forked linearly. Morphospecies and biospecies can (at least in individual cases) go back to different lineages and can therefore be para- or polyphyletic .
Chronological style concept
Another attempt to clearly delimit species in time is the chronological species concept ( chronospecies ). Here, too, the species is initially defined using another species concept (mostly the morphological species concept). Then, according to the criteria of this concept, the species boundaries between successive populations in a region are also defined. This concept is mainly used in paleontology and is therefore usually an extension of the morphological species concept by the time factor:
- A species is characterized by a sequence of chronologically consecutive populations whose individuals lie within a certain morphological range of variation.
This concept can be used well if there are practically complete findings.
Statistical style concept
In paleontology, especially in paleoanthropology, the assignment to species and even the assignment to genera on the basis of fossil bones alone proves to be difficult. Instead of a contravalent assignment, John Francis Thackeray therefore proposes a probabilistic assignment. Instead of asking whether one fossil belongs to species A and another to species B, the probability that both belong to the same species is calculated. For this purpose, the largest possible number of pairs of different morphometric measuring points of two individuals each, for which the species association is uncertain, is compared. The pairs of measured values always deviate from one another. They scatter in the form of a Gaussian normal distribution . Within this distribution it is defined in which interval around the mean value (e.g. 2 sigma ) both individuals are considered to belong to the same species. If the measuring points are outside the specified interval, the two individuals are considered to be of two different types.
At the beginning of the 21st century, between 1.5 and 1.75 million species had been described, around 500,000 of which were plants. However, it can be assumed that these are only a fraction of all existing species. Estimates suggest that the total number of all species on earth is significantly higher. The most far-reaching assumptions reached up to 117.7 million species at the end of the 1990s; however, the most common estimates were between 13 and 20 million species. A study published in 2011 estimated the number of species to be 8.7 ± 1.3 million, of which 2.2 ± 0.18 million marine life; However, this estimate only took into account species with a nucleus ( eukaryotes ), i.e. neither bacteria nor viruses.
Jay Lennon and Kenneth Locey of Indiana University estimated the number of species on earth to be 1 trillion (10 12 ) in March 2016 based on the results of 3 major projects treating microbes in medicine, the sea and soil . In particular, the small life forms of bacteria, arks and fungi have so far been greatly underestimated. Modern genome sequencing makes precise analyzes possible.
The total number of all animal and plant species that arose since the beginning of the Phanerozoic 542 million years ago are only estimated. Scientists assume around a billion species, some even estimate 1.6 billion species. Far less than one percent of this biodiversity has been preserved in fossil fuels , as the conditions for fossil formation are generally unfavorable. In addition, erosion and plate tectonics destroyed many fossils over the course of millions of years. By 1993, researchers had scientifically described around 130,000 fossil species .
It can be shown that when using the phylogenetic species concept, more species are distinguished than the biological species concept. The increase in the number of species, e.g. B. within the primates, which go back exclusively to the species concept used, has been called "taxonomic inflation". This has consequences for applied areas if they are based on a comparison of species lists. There are different relationships when comparing the number of species between different taxonomic groups, geographical areas, the proportion of endemic species and the definition of the need for protection of populations or areas in nature conservation.
- Neil A. Campbell : Biology. Spektrum Akademischer Verlag, Heidelberg 1997, ISBN 3-8274-0032-5 , p. 476 ff.
- Werner Kunz : What is a species? Tried and tested in practice, but vaguely defined. In: Biology in Our Time. Wiley-VCH, Weinheim 32, 1, 2002, pp. 10-19.
- Ernst Mayr : This is life - the science of life. Spektrum Akademischer Verlag, Heidelberg 1997, ISBN 3-8274-1015-0 .
- Ernst Mayr: Animal Species and Evolution. 6th edition. Belknap of Harvard University Press, Cambridge 1963, 1977; Species concept and evolution. Parey, Hamburg / Berlin 1967 (German).
- Ernst Mayr: Basics of the zoological system. Blackwell Wissenschaftsverlag, Berlin 1975, ISBN 3-490-03918-1 .
- Ernst Mayr: Evolution and the Diversity of Life. Springer-Verlag, 1979, ISBN 3-540-09068-1 .
- Peter Ax : The Phylogenetic System. Urban & Fischer bei Elsevier, 1997, ISBN 3-437-30450-X .
- Peter Ax: Systematics in Biology. Verlag Gustav Fischer, Stuttgart 1988, ISBN 3-437-20419-X .
- Ernst Mayr: A New Philosophy in Biology . R. Piper, Munich 1991, ISBN 3-492-03491-8 . Original edition: Toward a New Philosophy of Biology . The Belknap Press of Harvard University Press, Cambridge, Massachusetts and London 1988.
- Michael Ruse (Ed.): What the Philosophy of Biology is - Essays dedicated to David Hull . Kluwer Academic Publishers, Dordrecht 1989, ISBN 90-247-3778-8 . For the discussion of species especially: J. Cracraft, MT Ghiselin, P. Kitcher, EO Wiley and MB Williams
- Peter Heuer: Type, genus, system: a logical-systematic analysis of basic biological concepts. Publishing house Karl Alber, Freiburg i. Br. 2008, ISBN 978-3-495-48333-6 .
For detailed and current discussions of specific topics:
- Robert A. Wilson (ed.): Species - New Interdisciplinary Essays . The MIT Press, Cambridge, Massachusetts, London 1999, ISBN 0-262-23201-4 .
- Elliot Sober: Philosophy of Biology. 2nd Edition. Westview Press, 2000, ISBN 0-8133-9126-1 .
- Rainer Willmann : The kind in space and time. The species concept in biology and paleontology. Parey, Hamburg 1985, ISBN 3-489-62134-4 .
- Entry in Edward N. Zalta (Ed.): Stanford Encyclopedia of Philosophy .
- Deutschlandfunk, September 8, 2013: Above drawers: biologists struggle with the term species.
- Deutschland-Radio, December 15, 2005: Scientist proposes redefinition of the fluctuating concept of species.
- Telepolis, July 28, 2005: New host, new species.
- Art . In: Lexicon of Biology . Online edition, accessed December 11, 2014.
- Christopher D. Horvath: Discussion: Phylogenetic Species Concept: Pluralism, Monism, and History. In: Biology and Philosophy. Volume 12, No. 2, 1997, pp. 225-232, doi: 10.1023 / A: 1006597910504
- Ernst Mayr: What is a Species, and What is Not? In: Philosophy of Science. Volume 63, 1996, pp. 262-277 ( full text online).
- F. Pleijel, GW Rouse: Least-inclusive taxonomic unit: a new taxonomic concept for biology. In: Proceedings of the Royal Society London. Series B 267, 2000, pp. 627-630.
- Kevin de Queiroz: The General Lineage Concept of Species and the Defining Properties of the Species Category. In: RA Wilson (Ed.): Species: New Interdisciplinary Essays. MIT Press, 1999, ISBN 0-262-73123-1 , pp. 49-89.
- Fredrik Ronquist: Systematics - Charting the Tree of Life. In: Pablo Vargas, Rafael Zardoya (eds.): The Tree of Life. Sinauer Associates, 2014, ISBN 978-1-60535-229-9 .
- International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) Article 23
- International Code of Nomenclature of Bacteria: Bacteriological Code, 1990 Revision. Rule 12a, Names of Species
- International Code of Zoological Nomenclature online Article 5.1: Names of species.
- G. Becker: Compendium of the Zoological Nomenclature. Terms and symbols explained by official German texts. In: Senckenbergiana Lethaea. 81 (1), 2001, p. 10 ("epithetum specificum"), p. 12 ("epitheton specificum")
- Aristotle : Organon, doctrine of the categories. Chapter five (Αριστοτέλης: Κατηγορίαι). The entity that is preferably and first and foremost so called is that which is neither predicated of, nor is in any substrate, e.g. B. the particular person or the particular horse. Second beings are called both the species in which the first named beings are present, and their species, as well as the genera of these species; z. B. the definite man is present in man as in his kind, but the species of the kind is the living; second beings are called these, like man and the living. Albert Gustav Heydemann (ed. And transl.): The categories of Aristotle. G. Reimer Verlag, Berlin 1834, p. 3. (online) . Οὐσία δέ ἐστιν ἡ κυριώτατά τε καὶ πρώτως καὶ μάλιστα λεγομένη , ἣ μήτε καθ 'ὑποκειμένου τινὸς λέγεται μήτε ἐν ὑποκειμένῳ τινί ἐστιν, οἷον ὁ τὶς ἄνθρωπος ἢ ὁ τὶς ἵππος. δεύτεραι δὲ οὐσίαι λέγονται, ἐν οἷς εἴδεσιν αἱ πρώτως οὐσίαι λεγόμεναι ὑπάρχουσιν, ταῦτά τε καὶ τὰ τῶν εἰδῶν τούτων γένη · οἷον ὁ τὶς ἄνθρωπος ἐν εἴδει μὲν ὑπάρχει τῷ ἀνθρώπῳ , γένος δὲ τοῦ εἴδους ἐστὶ τὸ ζῷον · δεύτεραι οὖν αὗται λέγονται οὐσίαι, οἷον ὅ τε ἄνθρωπος καὶ τὸ ζῷον. Αριστοτέλης: Κατηγορίαι, Κεφάλαιον 5 (Wikisource) .
- Wolfgang Kullmann: Aristotle's scientific method in his zoological writings. In: Georg Wöhrle (Ed.): History of mathematics and natural sciences in antiquity. Volume 1: Biology. Franz Steiner Verlag, Stuttgart 1999, pp. 103-123. Here p. 110.
- DM Balme: Γένος and Ει̑̓δος in Aristotle's Biology . In: The Classical Quarterly . tape 12 , no. 1 , 1962, pp. 81-98 , JSTOR : 638031 .
- Αριστοτέλης : Περί τα ζώα ιστοριών . In: Aristotelis Opera. Walter de Gruyter, Berlin 1960. ( Των περί τα ζώα ιστοριών - Wikisource.)
- Pierre Maurice Marie Duhem : Le système du monde: histoire des doctrines cosmologiques de Platon à Copernic. Tome VI: Le reflux de l'aristotélisme (Henri de Gand, Duns Scot, l'essentialisme, les deux vérités ...). Hermann, Paris 1916, pp. 451–509. (10 volumes, 1913-1959).
- Ernst Mayr : The development of the biological world of thought - diversity, evolution and inheritance . Springer Verlag, Berlin / Heidelberg 2002. The essentialist concept of species, pp. 185f.
- Ernst Mayr: The development of the biological world of thought - diversity, evolution and inheritance. Springer Verlag, Berlin / Heidelberg 2002, p. 46.
- John Ray : Historia plantarum generalis. 1686, Tomus I, Liber I, Caput XX, pagina 40. Ut plantarum numerus iniri possit et earundem divisio recte institui oportet ut notas aliquas seu indicia specificas (ut vocant) distinctiones investigemus. Nobis autem diu multumque indagantibus nulla certior occurrit quam distincta propagatio ex semine. Quaecunque ergo Differentiae ex ejusdem seu in individuo, seu specie plantae semine oriuntur, accidentales sunt, non specificae. Hae enim speciem suam satione iterum non propagant. … Nam quae specie differunt speciem suam perpetuo servant, neque haec from illius semine oritur, aut vice versa.
- Carl von Linné : Philosophia botanica. 1751. Characteres, p. 99. No. 157. Species tot sunt, quot diversas formas ab initio produxit infinitum Ens; quae formae, secundum generationis inditas leges, produxere plures, at sibi semper similes.
- Carl von Linné: Philosophia botanica. 1751. Characteres, p. 101. No. 162. Naturae opus semper est Species (157), et Genus (159): Culturae saepius Varietas (158); Naturae, et Artis Classis (160), et Ordo (161). Species constantissimae sunt, cum earum generatio est vera continuatio.
- Ernst Mayr: The development of the biological world of thought - diversity, evolution and inheritance. Springer Verlag, Berlin / Heidelberg 2002, p. 139.
- Georges-Louis Leclerc de Buffon : Oeuvres complètes. Tome Cinquième, P. Duménil, éditeur, Paris 1775. De la Nature, Seconde vue, Quadrupèdes, xxxiij. L'empreinte de chaque espèce est un type dont les principaux traits sont gravés en caractères ineffaçables et permanens à jamais; mais toutes les touches accessories varient: also individu ne ressemble parfaitement à un autre.
- Jean-Baptiste de Lamarck : Philosophy zoologique, ou Exposition des considérations relatives à l'histoire naturelle des Animaux, tome premier. Dentu, Paris 1809, p. 21. La nature n'a réellement formé ni classes, ni ordres, ni familles, ni genres, ni espèces constantes, mais seulement des individus.
- Fernando Suárez Müller: Skepticism and history: the work of Michel Foucault in the light of absolute idealism. Publishing house Königshausen & Neumann, Würzburg 2004, p. 581.
- Bruno Streit, Markus Pfenninger, Klaus Schwenk: An earth full of species. Darwin's Legacy in Evolutionary Biology Today. In: Current Research. Research Frankfurt 3/2008, pp. 72-75, p. 72.
- Ernst Mayr: The development of the biological world of thought - diversity, evolution and inheritance. Springer Verlag, Berlin / Heidelberg 2002, p. 192.
- Charles Darwin : On the origin of species by means of natural selection or the preservation of favored races in the struggle for life . John Murray, London 1859. (German: About the origin of species through natural selection or the preservation of the favored races in the struggle for existence. Translated from English by HG Bronn. Sixth German edition, after the sixth English edition repeatedly revised and corrected by J. Victor Carus 1876. E. Schweizerbart'sche Verlagshandlung (E. Koch), Stuttgart 1876, p. 75) Page: DarwinEntstehung1876.djvu / 81 From these remarks it can be seen that I use the art term “Species” as an arbitrary and the For the sake of convenience, consider that it is applied to a number of individuals very similar to one another, and that it is not essentially different from the art term "variety" which is applied to less differing and even more fluctuating forms. Likewise, the expression “variety” is used only arbitrarily and for convenience in comparison to mere individual differences, p. 52. On the Origin of Species (1859) / Chapter II From these remarks it will be seen that I look at the term species, as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms. The term variety, again, in comparison with mere individual differences, is also applied arbitrarily, and for mere convenience sake.
- Alfred Russel Wallace : On the phenomena of variation and geographical distribution as illustrated by the Papilionidae of the Malayan region. In: Transactions of the Linnean Society of London. Volume 25, 1865, pp. 1-71. Here p. 12. “Species are merely those strongly marked races or local forms which, when in contact, do not intermix, and when inhabiting distinct areas are generally regarded to have had a separate origin, and to be incapable of producing a fertile hybrid offspring. But as the test of hybridity cannot be applied in one case in ten thousand, and even if it could be applied, would prove nothing, since it is founded on an assumption of the very question to be decided - and as the test of origin is in every case inapplicable– and as, further, the test of non-intermixture is useless, except in those rare cases where the most closely allied species are found inhabiting the same area, it will be evident that we have no means whatever of distinguishing so -called 'true species' from the several modes of variation here pointed out, and into which they so often pass by an insensible gradation ".
- Brockhaus' Konversationslexikon. Volume: A - Astrabad. 14th edition. FA Brockhaus, Leipzig / Berlin / Vienna 1894-1896, p. 941, article type (Latin species) . Among other things, the following statement was discussed: "Animals that produce reproductive young together belong to one and the same species."
- Erwin Stresemann : About the European tree creepers. In: Negotiations of the Ornithological Society in Bavaria. Volume 14, 1919, p. 64.
- Theodosius Dobzhansky : The genetic basis of speciation. (German translation of the 1st edition of Genetics and the Origin of Species ). Fischer Verlag, Jena 1939, p. 221.
- Ernst Mayr: Systematics and the Origin of Species. Columbia University Press, New York 1942, p. 120. "Species are groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups".
- Kevin de Queiroz: Ernst Mayr and the modern concept of species. In: PNAS. Volume 102, No. Suppl. 1, 2005, pp. 6600–6607, doi: 10.1073 / pnas.0502030102 , (full text)
- Ernst Mayr: The development of the biological world of thought - diversity, evolution and inheritance. Springer Verlag, Berlin / Heidelberg 2002, p. 219. Original: Ernst Mayr: The Growth of Biological Thought. The Belknap Press of Harvard University Press, Cambridge (Massachusetts) / London 1982. A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature.
- Ernst Mayr: The development of the biological world of thought - diversity, evolution and inheritance. Springer Verlag, Berlin / Heidelberg 2002, The importance of species in biology, p. 210f. Original: Ernst Mayr: The Growth of Biological Thought. The Belknap Press of Harvard University Press, Cambridge (Massachusetts) / London 1982.
- Cleveland P. Hickman, Larry S. Roberts, Allan Larson, Helen l'Anson, David J. Eisenhour: Zoologie. 13th updated edition. From the American by Thomas Lazar. German adaptation by Wolf-Michael Weber. Pearson Studies, Munich 2008, 10.2. Species: The typological concept of species, p. 306.
- "Species concepts [...] are, after all, humanly created approximations of reality in the natural world." Quoted from Chris Stringer : The Origin of Our Species. Penguin / Allen Lane, 2011, ISBN 978-1-84614-140-9 , p. 245.
- Ernst Mayr: Species concepts and definitions. In: Ernst Mayr (Ed.): The species problem. Publication No. 50 of the American Association for the Advancement of Science. Washington DC 1957, p. 2.
- Mary P. Winsor: Non-essentialist methods in pre-Darwinian taxonomy . In: Biology and Philosophy. 18 (3), 2003, pp. 387-400.
- John S. Wilkins: A History of the Idea. University of California Press, Berkeley / Los Angeles 2009, p. 5.
- John S. Wilkins: A History of the Idea. University of California Press, Berkeley / Los Angeles 2009. Essentialism and natural systems, p. 91.
- on the taxonomic use of behavioral characteristics cf. Drew Rendall, Anthony Di Fiore: Homoplasy, homology, and the perceived special status of behavior in evolution. In: Journal of Human Evolution. 52, 2007, pp. 504-521. doi: 10.1016 / j.jhevol.2006.11.014
- Georg Fuchs: General Microbiology . Ed .: Georg Fuchs. 9th edition. Georg Thieme Verlag, Stuttgart / New York 2014, ISBN 978-3-13-444609-8 , p. 539 .
- Daniel Dykhuizen: Species Numbers in Bacteria. In: Proceedings of the California Academy of Sciences. Volume 56, Supplement I, No. 6, 2005, pp. 62-71.
- Frederick M. Cohan: What are bacterial species? In: Annual Review of Microbiology. 56, 2002, pp. 457-487.
- Ernst Mayr: Evolution and the diversity of life. Springer-Verlag, 1979, ISBN 3-540-09068-1 , p. 234.
- Ernst Mayr: Evolution and the diversity of life. Springer-Verlag, 1979, ISBN 3-540-09068-1 , pp. 234f.
- Rolf Löther: The mastery of the manifold. Philosophical foundations of taxonomy . Gustav Fischer, Jena 1972; Michael T. Ghiselin: A radical solution to the species problem. In: Systematic Zoology. 23, 1974, pp. 536-544; David L. Hull: Are species really individuals? In: Systematic zoology. 25, 1976, pp. 174-191.
- George G. Simpson: The species concept. In: evolution. 5 (4), 1951, pp. 285-298.
- Ulf von Rauchhaupt : About the decay of species . In: Frankfurter Allgemeine Sonntagszeitung. 20th November 2016.
- Peter Sitte, Elmar Weiler, Joachim W. Kadereit, Andreas Bresinsky, Christian Körner: Textbook of botany for universities . Founded by Eduard Strasburger . 35th edition. Spektrum Akademischer Verlag, Heidelberg 2002, ISBN 3-8274-1010-X , p. 10.
- Joel Cracraft: The seven great questions of systematic biology, an essential foundation for conservation and the sustainable use of biodiversity. In: Annals of the Missouri Botanical Garden. Volume 89, No. 2, 2002, pp. 127-144.
- P. Hammond: The current magnitude of biodiversity. In: VH Heywood, RT Watson (Ed.): Global Biodiversity Assessment. Cambridge University Press, Cambridge 1995, ISBN 0-521-56403-4 , pp. 113-138.
- Camilo Mora et al .: How Many Species Are There on Earth and in the Ocean? In: PLoS Biol . Volume 9, No. 8, 2011, Item No. e1001127. doi: 10.1371 / journal.pbio.1001127
- Kenneth J. Locey, Jay T. Lennon: Scaling laws predict global microbial diversity. In: PNAS . March 30, 2016, accessed May 3, 2016. doi: 10.1073 / pnas.1521291113
- Billions of species could live on earth , orf.at, May 3, 2016, accessed on May 3, 2016.
- Peter Wellnhofer : The great encyclopedia of the pterosaurs. Mosaik Verlag, Munich, 1993, p. 13. From: E. Kuhn-Schnyder (1977): The story of life on earth. In: Communications from the Natural Research Society of the Canton of Solothurn. 27. The beginning of the Cambrian is given by Wellnhofer as 590 million years.
- Nick JB Isaac, James Mallet, Georgina M. Mace : Taxonomic inflation: its influence on macroecology and conservation. In: Trends in Ecology and Evolution. Volume 19, No. 9, 2004, pp. 464-469.