Evolutionary history

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Display board from the Cambrian to the Holocene . The Precambrian is shown as a narrow bar below, but it was the longest period in the history of the earth (see time table below). The animal phyla and species are not shown according to a phylogenetic order, but only as examples for the geological periods. For time scale, see Phanerozoic .

The evolutionary history describes the fact that in the course of the earth's history living beings appeared for the first time at certain times and many of them also disappeared again, that species have changed and new species, new plant and animal strains have emerged. The evolutionary history can be objectively traced on the basis of fossil finds . In contrast to this, the evolution theories deal with the possible explanations ( explanatory models ) for evolution. Both belong to the research areas of evolutionary biology .

History of science

Fundamental discoveries in geology and paleontology preceded the various theories of evolution . As early as the 17th and 18th centuries it was known that the layers of sedimentary rocks lying on top of each other are of different ages. Most of the time, the lower layers are older, i.e. they were deposited earlier, and the layers above are younger because they were deposited afterwards (→  stratigraphic principle ). It was also known for a long time that such layers contain fossilized remains that apparently came from living beings, so-called fossils . In the late 18th and early 19th centuries, French geologists and biologists collected fossils of plants and animals in the sedimentary rocks of the overburden of the French layered plains formed in the Permian, Triassic, Jurassic and Cretaceous periods and systematically described them. In the older basement they also found some well-preserved fossils.

Georges Cuvier and others found that the relative age relationships that result from the sequence of layers from bottom to top are also reflected in the fossil content. Fossils of the same type were only found in layers of roughly the same age. It was concluded from this that certain animal and plant species could only have appeared on earth from a certain point in time, since no corresponding fossils could be found in the older sedimentary rocks below. Likewise, certain animal and plant species had to have disappeared from the earth - extinct - at a certain point in time , because on the one hand they no longer occur in today's living world and they can no longer be found in younger sedimentary rocks.

A systematic comparison of the fossil fauna (and flora ) with the relative age of the layers in which they were contained showed that the living world has not only changed significantly over the course of the earth's history, but that this change is relatively continuous, almost literally Can be traced “from shift to shift”. It was also found that more extensive geological periods can be distinguished in which certain groups of organisms dominated before they finally became extinct. All of these observations became the basis of the principle according to which the relative age of the strata can be determined with the aid of the fossils contained therein (→  biostratigraphy ). It was also observed that the complexity of the organisms increases with the age of the layers of the find. In the oldest fossil-bearing strata, " lower animals " such as sponges , trilobites and armpods are still predominantly simply built and live exclusively in the sea , while in younger strata both more complex "lower animals" ( modern cephalopods , sea ​​urchins , flying insects ) and an increasing number can be found There is a wide variety of vertebrates that no longer only lived in the sea but also on land.

These observations prompted the Enlightenment pioneers of modern natural sciences to consider how the observed changes in the fauna and flora of “ primeval times ” could have taken place naturally. The biologist Jean-Baptiste de Lamarck speculated that animal forms that appeared later could have emerged as descendants of the earlier ones. Can that meant that species change and develop new other forms, in other words, evolve into other forms or evolve, can. Lamarck was thus one of the first to replace the biblical concept of the immutability of species with the idea of evolution . His hypothesis on the mechanism behind evolution (→  Lamarckism ) later proved to be largely inaccurate, but motivated other scientists to look for better explanations. Finally, the evolutionary theory developed by Charles Darwin and Alfred Russel Wallace in the middle of the 19th century, which is still valid today in its main features and in which natural selection plays a central role, finally prevailed . This was later expanded and modified by Wallace himself as well as by August Weismann , Ernst Mayr , Theodosius Dobzhansky and other pioneers of modern evolutionary biology .

Change of habitats and environmental conditions

The earth has been a dynamic planet since the beginning of its existence . That is why - in the millions of years that are difficult for humans to grasp - environmental and living conditions on earth are constantly changing due to global processes, with partly one-sided, partly reciprocal influences. These processes include shifts in tectonic plates , extensive volcanism , changes in global climate and global fluctuations in sea level . Triggered by these continuous changes, among other things, the existing forms of life in the plant and animal world either continued to develop over the course of millions of years into new forms that were better able to cope with the new environmental factors , or they died out. In times of particularly adverse conditions, there were real ecological crises - mass extinctions - during which the biodiversity decreased massively. For some such events, not only terrestrial geological, but also cosmic causes ( asteroid impact , gamma-ray flash ) have been proven or at least considered. However, after such crises, biodiversity increased again in a relatively short period of time, a process known as adaptive radiation . It can be observed in the fossil record that some animal groups, which were previously only represented with a few small forms, suddenly developed an enormous variety of forms, which also included many large, sometimes even gigantic forms. Other animal groups lost their former dominance in the course of mass extinction. One of the most popular examples of such a turnaround in the animal world is the disappearance of the non-avian dinosaurs at the end of the Cretaceous Period and the ensuing dawn of the "Age of Mammals " from which man ultimately sprang.

Temporal sequence in the formation of the early living beings

Evolution of living things over
4.1 billion years. No logarithmic , but rather a linear time scale was deliberately used for this representation . So is optically clear that the Precambrian following Phanerozoic is relatively short in relation to the Earth's history. The small rectangle at the top right corresponds to the above timetable.

The earliest evidence of life is relatively close in time to the date of origin of the earth assumed today (in a protoplanetary disk ). The atmosphere of the very early Earth did not yet contain oxygen. The earliest prokaryotic microorganisms met their energy needs through chemosynthesis . There were many - from today's perspective - "extremophile" single-cell organisms that could live and multiply under the abiotic conditions of that time. After the emergence and spread of strong photosynthesis operated prokaryotes , especially blue-green algae , there was worldwide in a drastic increase of the oxygen content of the water and the Earth's atmosphere (see great oxygenation event ) and thus to global changes in living conditions. The rise in oxygen levels in the Precambrian waters began long before the GOE and favored biomineralization .

After the eukaryotes and then also multicellular organisms ( Parazoa and Eumetazoa ) had emerged through symbiogenesis and endosymbiosis, the multicellular organisms developed higher, which at the end of the Precambrian only showed themselves in the Ediacaran fauna . In the Cambrian, during the Cambrian Radiation , many animal phyla emerged almost simultaneously. The latter was the starting point for the almost unmanageable diversity that exists on the earth today, especially of living beings built with bilateral symmetry.

literature

See also

Individual evidence

  1. ^ Emil Kuhn-Schnyder, Hans Rieber: Palaeozoology, morphology and systematics of extinct animals. Stuttgart 1984.
  2. ^ Rüdiger Wehner, Walter Gehring: Zoologie. Stuttgart 1990.
  3. ^ Neil A. Campbell, Jane B. Reece: Biology. Heidelberg / Berlin 2003.
  4. ↑ Wolfgang Schad (Hrsg.): Evolution as a principle of understanding in the cosmos, man and nature. Free Spiritual Life Publishing House, Stuttgart 2009, pp. 223-251.
  5. ^ Neil A. Campbell , Jane B. Reece : Biology. Spektrum-Verlag, Heidelberg / Berlin 2003, ISBN 3-8274-1352-4 .
  6. ↑ Alexandre Brongniart , Georges Cuvier : Essai sur la geographie minéralogique des environs de Paris. In: Journal des mines. Volume 23, No. 138, 1808, pp. 421-458.
  7. ↑ Georges Cuvier : Recherches sur les ossemens fossiles ou l'on rétablit les caractères de plusieurs animaux dont les révolutions du globe ont détruit les espèces . 4 volumes. Dufour et d'Ocagne, Paris 1812. (4th edition. 12 volumes. Paris 1835–1837)
  8. ^ Jean-Baptiste de Lamarck : Philosophy zoologique, ou, Exposition des considérations relative à l'histoire naturelle des animaux. Paris 1809 (German translation by Arnold Lang: Jena 1876)
  9. ↑ Christopher Scotese : Atlas of Earth History, Paleogeography. Paleomap Project, Arlington, Texas 2001. ( www.scotese.com )
  10. ^ Vincent Courtillot , Paul Renne: Comptes Rendus Geoscience. 335 (1), 2003, pp. 113–140 (mantleplumes.org; PDF)
  11. ^ J. David Archibald: Extinction and Radiation: How the Fall of Dinosaurs Led to the Rise of Mammals. Johns Hopkins University Press, Baltimore (MD) 2011, ISBN 978-0-8018-9805-1 .
  12. ↑ Eukaryotes: A New Timeline of Evolution. Max Planck Society, May 24, 2015. (www.mpg.de)
  13. ↑ Manfred Schidlowski : Early Evolution of Life on Earth: Geological and Biogeochemical Evidence. In: ZGW. 37, 4-5, Berlin 2009, pp. 237-260. (zgw-online.de; PDF)
  14. ↑ Armen Mulkidjanian, Andrew Bychkov et al: Origin of first cells at terrestrial, anoxic geothermal fields. (biophys.ru; PDF)