Bilaterality

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Bilaterality (from Latin to "twice", in compositions "double" -, "two" -, latus . "Side") means "two-sidedness", related terms are the multilateral (versatile) and unilateral (one-sided).

politics

In politics, the adjective bilateral is used for negotiations and agreements that take place exclusively between two different parties. Bilateral diplomacy is still common in the form of many treaties between two states. Embassies and state visits mainly serve this function.

A supranational subject of international law like the European Union can also be a partner for a bilateral agreement; this is the case with the " bilateral agreements between Switzerland and the EU ".

The oldest bilateral treaty still in force for Germany is the Friendship, Trade and Shipping Treaty between Prussia and the states of the German Customs Union on the one hand and Argentina on the other from September 19, 1857.

biology

The median plane divides the body into a left and a right half, which are mirror-symmetrical to each other

In biology we speak of bilaterality ("two-sidedness") when the left and right halves of an organism are mirror-symmetrical to one another . Many plant organs and most tissue animals , including humans, have a bilateral (also: bilaterally symmetrical) blueprint , so they can only be geometrically divided along their median plane (here at the same time mirror plane and plane of symmetry) into two externally identical, mirror - image halves. Living beings or their parts (e.g. foliage leaves ) with only a single mirror plane, in which the sides are the same, but the top and bottom are shaped differently, are called " dorsiventral " ( zygomorphic flowers , bifacial leaves ). Bilaterality is almost always accompanied by dorsoventrality.

In the animal kingdom, bilaterality is the typical form of symmetry in the body . Around 95 percent of the multicellular animals - that is, all animals with the exception of the asymmetrically built " tissue-less " ( sponges and placozoa ) and the radially symmetrical cnidarians (" jellyfish " and rib jellyfish → " radiata ") - belong to the Bilateria (also: Bilateralia, " Bilateral animals "). They owe this name to the mirror-symmetrical morphology , which is also one of their jointly derived characteristics .

The typical characteristic of animals to actively move towards their food is considered to be the cause of the development and widespread distribution of bilateral symmetry in the animal kingdom . In the evolution of Bilateria, this purposeful locomotion produced a front and a rear end of the body and thus also a left and right side of the body. As a further consequence, a head region ( cephalization ) was created at the front end with simultaneous brain formation (cerebralization) for the perception and processing of sensory impressions and a tail region at the rear end. The formation of the skeleton is also functionally related to bilateral symmetry and locomotion , because the initially crawling and winding locomotion required a hydroskeleton as an abutment for external muscles . The echinoderms living on the seabed (e.g. starfish ) have a symmetry form that is unique within Bilateria : the adult animal has a five-pointed radial symmetry ( pentamerism ), but the larva still shows the mirror symmetry that is so typical for Bilateria and thus makes the taxonomic one Affiliation of the echinoderms recognizable. In contrast to the primary radial symmetry of the cnidarians, their radial symmetry is a secondary adaptation and is interpreted as a consequence of a fixed way of life in the phylogenetic past in a phase without locomotion.

Unlike an animal body with radial symmetry through which many mirror planes can be laid (polysymmetry), a body with bilateral symmetry has a single mirror plane (monosymmetry). Clear planes and directions on the body can be defined from this alignment axis , which simplifies the anatomical description.

Other uses

  • In economics (economics) used the term to different market structures and combinations thereof ( monopoly , oligopoly and Polypol to describe).
  • In ethnology the term is used in relation to kinship. It describes the situation-dependent reference to either the relatives on the maternal or paternal side.

Individual evidence

  1. ↑ bilateral . In: Lexicon of Biology . Spectrum Academic Publishing House. Heidelberg. 1999. Retrieved September 25, 2016.
  2. ↑ a b c Bilateria . In: Lexicon of Biology . Spectrum Academic Publishing House. Heidelberg. 1999. Retrieved September 25, 2016.
  3. ↑ dorsiventral . In: Lexicon of Biology . Spectrum Academic Publishing House. Heidelberg. 1999. Retrieved October 3, 2016.
  4. ↑ symmetry . In: Lexicon of Biology . Spectrum Academic Publishing House. Heidelberg. 1999. Retrieved October 3, 2016.
  5. ↑ axis . In: Lexicon of Biology . Spectrum Academic Publishing House. Heidelberg. 1999. Retrieved October 3, 2016.
  6. ^ Hynek Burda General Zoology. Verlag Eugen Ulmer, Stuttgart 2005, ISBN 3-8001-2838-1 , p. 54.

Web links

Wiktionary: bilateral  - explanations of meanings, word origins, synonyms, translations