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No. 108: Nov-Dec 1996

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Lake victoria's cichlid fishes: can random mutations explain them?

Lake Victoria is Africa's largest lake (420 kilometers long, but only 69 meters at its deepest). It is also the home of more than 300 species of cichlid fishes. Ordinarily, that number of different species would pose no problem for the biologists -- look at the 400 or so species of hummingbirds in Central and South America! Lake Victoria, however, is a very young lake, and all of these cichlid fishes are endemic. Therefore, they must have evolved rather rapidly.

Recent seismic surveys of Lake Victoria and piston cores from its deepest parts by T.C. Johnson et al have surprised everyone: Lake Victoria was completely dry 12,400 years ago. Nor were there deeper "satellite" lakes that could have served as refuges for Lake Victoria's biota during extreme droughts. It is difficult to avoid the conclusion that the present-day 300+ species of cichlid fishes all evolved in less than 12,400 years.

This being so, can random mutations -- the accepted source of evolutionary novelty -- have generated so many new species in such a short time? That would be one new species every 40 years or so on the average.

(Johnson, Thomas C., et al; "Late Pleistocene Desiccation of Lake Victoria and Rapid Evolution of Cichlid Fishes," Science, 273:1091, 1996)

Comments. Of course, hybridization may have accelerated the evolution of the 300+ species. Perhaps "adaptive" or "purposeful" evolution might have sped up the process, but this latter concept -- assuming it exists at all -- is not at all understood and highly controversial. (For more on adaptive evolution, see: SF#100, SF#96, SF#64, and pp. 180-181 in Science Frontiers (the book). This book is described at here.

As Lake Victoria began filling up again after the Pleistocene drought, the many open niches must have resembled the situation on the Galapagos when the "pioneer" finches first arrived, took advantage of the many new opportunities for making a living and, as the story goes, evolved into the several species known as Darwin's finches.

From Science Frontiers #108, NOV-DEC 1996. 1996-2000 William R. Corliss

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  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987