page_title: Evolution
section_title: Species splitting
hierarchical_section_title: Evolution / Darwin's theory / Species / Species splitting
caption_attribution_description: Originally uploaded 25 feb 2004 13:42 to nl.wikipedia.org by w:nl:Gebruiker:GerardM, with the summary "Met toestemming fotgraaf." Permission: nl:Gebruiker:GerardM/Ron Offermans
context_page_description: Evolution is a biological process. It describes how living things change over a long time. The explanation of how this process works and how living beings have come to be the way they are is called the theory of evolution.
  Earth is very old. By studying the layers of rock that make up Earth's crust, scientists can find out about its past. This kind of research is called historical geology.
  It is known that living things have changed over time, because their remains can be seen in the rocks. These remains are called 'fossils'. This proves that the animals and plants of today are different from those of long ago. The older the fossils, the bigger the differences from modern forms. This has happened because evolution has taken place. That evolution has taken place is a fact, because it is overwhelmingly supported by many lines of evidence. At the same time, evolutionary questions are still being actively researched by biologists.
  Comparison of DNA sequences allows organisms to be grouped by how similar their sequences are. In 2010 an analysis compared sequences to phylogenetic trees, and supported the idea of common descent.
context_section_description: Two groups that start the same can also become very different if they live in different places. When a species gets split into two geographical regions, a process starts. Each adapts to its own situation. After a while, individuals from one group can no longer reproduce with the other group. Two good species have evolved from one.
  A German explorer, Moritz Wagner, during his three years in Algeria in the 1830s, studied flightless beetles. Each species is confined to a stretch of the north coast between rivers which descend from the Atlas mountains to the Mediterranean. As soon as one crosses a river, a different but closely related species appears. He wrote later:
  "... a [new] species will only [arise] when a few individuals [cross] the limiting borders of their range... the formation of a new race will never succeed... without a long continued separation of the colonists from the other members of their species".
  This was an early account of the importance of geographical separation. Another biologist who thought geographical separation was critical was Ernst Mayr.
  One example of natural speciation is the three-spined stickleback, a sea fish that, after the last ice age, invaded freshwater, and set up colonies in isolated lakes and streams. Over about 10,000 generations, the sticklebacks show great differences, including variations in fins, changes in the number or size of their bony plates, variable jaw structure, and color differences.
  The wombats of Australia fall into two main groups, common wombats and hairy-nosed wombats. The two types look very similar, apart from the hairiness of their noses. However, they are adapted to different environments. Common wombats live in forested areas and eat mostly green food with lots of moisture. They often feed in the daytime. Hairy-nosed wombats live on hot dry plains where they eat dry grass with very little water or nutrition in it. Their metabolic rate is slow and they sleep most of the day underground.
  When two groups that started the same become different enough, then they become two different species. Part of the theory of evolution is that all living things started the same, but then split into different groups over billions of years.
caption: The three-spined stickleback (Gasterosteus aculeatus)
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