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Classification: usually by logical division downwards: how many species are classified and what weight do the different characteristics have: "progressive" or "downwards classification". (Actually identification).
Therefore later: "Upwards classification: hierarchical arrangement of ever-growing groups of related species into classes.
Darwin's method confirmed the upward classification and thus triggered a scientific revolution.
Classification/20th Century (1950) two new schools:
a) Numerical Phenetics
Cladism: the cladist system is intended to reveal the history of the tribe only, while the evolutionary system strives to form taxa from the most similar and closely related species
(useful for ecology and biology).
Both species can continue to coexist, because they have very different objectives.
Systematics: not only to describe but to contribute to understanding.
Def Class/Biology/Mayr: Grouping of entities that are similar and related to each other.
Classification: two important functions: a) recovery of information. b) comparative research. Information storage.
1) Classes as homogeneous as possible
2) Attribution according to most common characteristics,
3) If the differences are too great, create a new class
4) The degree of difference between classes is ordered in a hierarchy.
Taxonomy: two steps:
1) Differentiation of species (microtaxonomy).
2) Classification of species into related groups (macrotaxonomy).
Microtaxonomy: The delineation of the species
"Species Problem": Species usually means "organism type". Problem: Males and females are also different types of organisms, just like young and adult organisms.
Def "Variety": (Linné, even Darwin): Deviations that are slightly smaller than those of a new species. ("typological" or "essential concept of species"). ("Common essence" ("Nature")).
"Typological concept of species: four characteristics:
1) Common "nature".
2) Between the species sharp discontinuity
3) Each species is spatially and temporally constant.
4) Possible variation within the species is strictly limited. ("Natural kind").
MayrVsTypological Concept of Species: Darwin refutes the notion of the "constancy of species". Populations vary geographically, individuals vary within a population. In the animate nature there are no types or essences!
Def twin species: (discovered only recently: spatially separated, but equally developed, discovered in almost all animal species), forces a new criterion for the delineatation of species: reproductive isolation of populations.
Biological Concept of Species (VsTypological Concept of Species): derives from this criterion of the lack of reproduction among one another.
Def Species Taxa: special populations or population groups that correspond to the species definition. They are entities ("individuals") and cannot be defined as such. Individuals cannot be defined, but are merely described and delineated.
Macrotaxonomy: The classification of species (in superordinate groups)
Groups: Usually easily recognizable: birds, butterflies, beetles.
Downward classification (actually identification). Dichotomy (Aristotelian), high time of medical botany.
E.g. warm-blooded or not warm-blooded, with feathers or not.
Upwards Classification/Mayr: Even Linné himself from 1770 onwards: better suited. Classes are distinguished and then grouped into superordinate groups. Unfortunately no strict methodology. There was no theoretical basis for the hierarchy.
Functional Classification: Sub-form of the upwards classification. Only selected features.
Two criteria: genealogy (common descent) and degree of similarity (extent of evolutionary change).
Causal classification: E.g. diseases according to causes: pathogen, aging process, toxic substances, genes, malignant changes, harmful radiation, etc.
Any classification that takes into account the causes is subject to severe restrictions and can never become a purely artificial system.
"Taxon": Separate group of offspring. Each taxon consists of the descendants of the next common ancestor. "Monophyletic".
Genealogy: Does not a classification make! Similarity cannot be neglected, because the diverging branches were subject to changes of varying extend. Result: Classification into families, genera, divisions, orders.
Homology/Mayr: Relationship between species and higher taxa is shown by the occurrence of homologous features. I.e. a feature derived from the same feature of its next common ancestor.
You must always infer homology!
There is a lot of evidence for homology, e.g. position of a structure in relation to other structures, also transitional forms with fossil ancestors
Das ist Biologie Heidelberg 1998