Cerebralization

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Skulls of humans , chimpanzees , orangutans and macaques with information on the mean brain weight

As Zerebralisation (also: Cerebralisation or Encephalisation ) is defined as the evolutionary development of a concentration of nerve cells , from which the course of the phylogeny several times independently of one another a central coordinating body - a brain - formed. A special case of the event is the evolutionary development of the cerebral cortex in humans, the corticalization .

In the course of human tribal history and hominization , the increase in brain volume was a characteristic feature of its evolution (see table on the right).

Development of the brain in the course of evolution

The following important information is missing from this article or section:
The exact description of the sequence of evolutionary steps between jellyfish and mammal is missing. There is a lack of brain development in other animal groups, e.g. B. insects.
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Taxon Brain volume
in cm 3
Chimpanzees about 400
Sahelanthropus tchadensis 365
Ardipithecus ramidus 280-350
Australopithecus afarensis 458
(335-580)
Australopithecus africanus 464
(426-502)
Homo rudolfensis approx. 750
(501–950)
Homo habilis 610
(544-674)
Homo ergaster 764
(640-888)
Homo erectus 1003
(956-1051)
Homo antecessor about 1000
Homo heidelbergensis 1204
(1130-1278)
Neanderthals 1426
(1351-1501)
homo sapiens 1478
(1444-1512)

In the course of evolution, the brain has developed from simply constructed preliminary stages into an increasingly complex system. Jellyfish are among the oldest organisms still in existence today that have a simple nervous system made up of a network of neurons. In contrast to radially symmetrical animals such as jellyfish and starfish , in animals that (like worms ) prefer one direction of movement, the nerve and sensory cells are concentrated at one of their ends (called the "front"), i.e. where the stimuli relevant to movement accumulate.

If this blueprint was retained in the course of evolution, a distinctive body part, called the head , developed independently of one another on the so defined front in different groups of animals , which encloses and protects the brain.

In humans, the brain stem is the genetically oldest part of the brain, at the lower end of which the spinal cord is attached. Numerous automatic and reflex-like processes are controlled in the brain stem. The cerebellum , for example, sense of balance and motor skills processed, the diencephalon u. a. involved in sleep- wake control and in pain perception . The cerebrum finally, for example, to memory and thought processes involved.

Benchmark

In mammals in particular , the encephalization quotient (EQ) - the ratio of brain mass to body mass - serves as a measure of the complexity and the associated cognitive abilities of species of different sizes .

The EQ indicates the ratio of the brain weight of an animal species to the calculated average brain weight that other animals with the same body weight have or that they would theoretically have if they had the same body weight.

An animal species with an approximately average value can be determined as a reference species. An EQ of 1 then means that the ratio of brain weight and body weight for the species in question corresponds to the value for the reference species. When compared with the cat as the reference species for mammals, the EQ of humans is 7.4–7.8, that of chimpanzees 2.2–2.5.

Consequences of cerebralization

Since the brain is a very energy-consuming organ, cerebralization means an increased energy requirement through food : Although the human brain contains only 2% of body weight, it requires around 20% of the basal metabolic rate .

A significant increase in the brain volume of newborns in the course of evolution is only possible if the birth canal expands accordingly.

literature

  • Adolf Portmann : Introduction to the Comparative Morphology of Vertebrates, p. 141, Chapter Cerebralization, Basel 1976, 5th revised edition, Schwabe & Co, ISBN 3-7965-0668-2
  • Sally C. Reynolds and Andrew Gallagher (Eds.): African Genesis: Perspectives on Hominin Evolution. Cambridge University Press, New York, 2012 [2]

Web links

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

Individual evidence

  1. ^ A b Gisela Grupe, Kerrin Christiansen, Inge Schröder and Ursula Wittwer-Ofen: Anthropologie. An introductory textbook. Springer, 2005, p. 15 [1] ISBN 978-1-107-01995-9
  2. ↑ Henke and Rothe, 1998
  3. ↑ Storch et al. , 2001
  4. ^ Ronald M. Nowak: Walker's mammals of the world. 6th edition. Johns Hopkins University Press, Baltimore 1999, p. 613
    Wolfgang Maier: Primates, Primaten, Herrentiere. In: Wilfried Westheide, Reinhard Rieger (Ed.): Special Zoology. Part 2. Vertebrate or skull animals. Spectrum Academic Publishing House, Heidelberg / Berlin 2004, p. 573
  5. ↑ a b c d e f g h i j k Matthew M. Skinner and Bernard Wood : The evolution of modern human life history - a paleontological perspective. In: Kristen Hawkes and Richard R. Paine (Eds.): The Evolution of Modern Human Life History. School of American Research Press, Santa Fe 2006, p. 351, ISBN 978-1-930618-72-5 . - The arithmetic mean and in brackets the 95% confidence interval are shown .
  6. ^ Gen Suwa et al .: The Ardipithecus ramidus Skull and Its Implications for Hominid Origins. In: Science. Volume 326, 2009, pp. 68, 68e1-68e7, doi: 10.1126 / science.1175825
  7. ↑ Gary J. Sawyer, Viktor Deak: The Long Way to Man. Life pictures from 7 million years of evolution. Spektrum Akademischer Verlag, Heidelberg, 2008, p. 79
  8. ↑ Friedemann Schrenk : The early days of man. The way to Homo sapiens , CH Beck, 1997, p. 70
  9. ↑ Harry J. Jerison: Evolution of the Brain and Intelligence . Academic Press, 1973, ISBN 0123852501 .