The Red Sea is one of the most diverse regions of the world ocean. Especially the presence of a high endemism ratio among its species shows that isolation and recolonisation processes during sea level variations of the past have made this water body to what it is today: a centre of speciation (forming of new species). The high endemism shows further that there is a high degree of adaptation to the specific environmental conditions characterized by high temperatures, aridity and high salinity. In contrast to the Gulf that has similar conditions, the Red Sea has deep waters that go up to more than 2000 m. Because of the sill at Bab el Mandeb this deep water body is excluded from the general oceanic circulation of cold deep sea waters. The deep waters of the Red Sea are formed through sinking of surface waters in the north. In consequence, the Red Sea has the worldwide warmest deep waters of 20.5-21.5 ° C (in the world ocean the respective deep sea temperatures are around 2°C). This results in a high degree of endemicity of the Red Sea Fauna (around 30%) and shallow water species of the Indian Ocean adapting to high pressure and reaching their highest depths within their distribution limits. With this, it gets clear that the Red Sea is a laboratory of evolution and very significant for understanding adaptation processes.