About a dozen lakes in the would are up to three orders of magnitude older than most
others. Lakes Tanganyika (East Africa) and Baikal (Siberia) have probably existed in some
form for 12-20 million years, maybe more. Such lakes can have different origins, sizes,
shapes, depths and limnologies, but, in contrast to short-lived (mostly post-glacial)
lakes, they have exceptionally high faunal diversity and levels of endemicity. A multitude
of patterns and processes accounting for these explosive radiations have recently been
documented, most of them based on particular groups in certain lakes, but comparative
research can detect repeated patterns. No special speciation mechanism, exclusive to
ancient lakes, has been demonstrated, although cases of ultra-rapid speciation have been
documented. Extant diversity results not by simple accumulation, but by a complex process
of immigration, speciation and extinction.