December 9, 2006 | David F. Coppedge

Fish Species in African Lake Diversified Rapidly

Two related articles in the Public Library of Science (PLoS) show that a large number of species can branch out of a small population in a short time.  Hobbyists familiar with tropical fish appreciate how wide is the variety found within Cichlids.  In the first article,1 the author alleged that in the last 15,000 years, the number of cichlid species living in the lake grew from a handful to hundreds.  Nearby Lake Malawi, which is supposedly much older, boasts no better variety of cichlids.
    Just as dog breeders select for a desired trait, the environment that each group of fish finds itself in selects for genes that cause the fish to survive well in that environment.  Isolation of the new “breed” of fish causes the combination of genes to be preserved.  The surprise to scientists was the speed at which this happened, compared to their expectations:

Though Lake Victoria cichlids appear millions of years younger than their counterparts in nearby Lake Malawi, both groups display an enormous range of physical and behavioral traits.  This staggering diversity in such young species provides compelling evidence for adaptive radiation, which occurs when divergent selection operates on ecological traits that favor different gene variants, or alleles, in different environments.  When divergent selection on an ecological trait also affects mate choice—promoting reproductive isolation of diverging populations—ecological diversity and speciation may proceed in tandem and quickly generate numerous new species.

Another surprise was to find that natural selection had succeeded in eliminating gene variety in some groups, “fixing” the gene: offspring contained only one type gene, recessive or dominant, and variety has been eliminated:

Despite substantial theoretical and some experimental support for such “by-product speciation,” few studies have shown that selection has “fixed” alleles (that is, driven its frequency in a population to 100%) with different effects on an adaptive trait in closely related populations.  But now, Yohey Terai, Norihiro Okada, and their colleagues have bridged that gap by demonstrating divergent selection on a visual system gene that influences both ecological adaptation and mate choice in cichlids.

In another paper in PLoS Biology,2 the author demonstrates that it really was the environment that produced the variety of characteristics within the Cichlid population:

Divergent natural selection acting on ecological traits, which also affect mate choice, is a key element of ecological speciation theory, but has not previously been demonstrated at the molecular gene level to our knowledge.  Here we demonstrate parallel evolution in two cichlid genera under strong divergent selection in a gene that affects both.  Strong divergent natural selection fixed opsin proteins with different predicted light absorbance properties at opposite ends of an environmental gradient.  By expressing them and measuring absorbance, we show that the reciprocal fixation adapts populations to divergent light environments.  The divergent evolution of the visual system coincides with divergence in male breeding coloration, consistent with incipient ecological by-product speciation.


1Gross L (2006), “Demonstrating the Theory of Ecological Speciation in Cichlids,” PLoS Biology 4(12): e449 DOI: 10.1371/journal.pbio.0040449.
2Terai Y, Seehausen O, Sasaki T, Takahashi K, Mizoiri S, et al. (2006), “Divergent selection on opsins drives incipient speciation in Lake Victoria cichlids,” PLoS Biology 4(12): e433.DOI: 10.1371/journal.pbio.0040433.

This is exactly what creationists have been saying all along: it doesn’t take long for genetic variation and the environment to produce the variety of species we see.  All species of canines could have descended from one pair on an Ark a few thousand years ago.  From wolves to Chihuahuas, all dogs are of the “dog” kind, and it didn’t take millions of years for their “adaptive radiation.”  In fact, it could have taken only hundreds of years in some cases.  The environment they found themselves in selected for the traits best suited to that environment.  For an evolutionist accustomed to speaking in millions of years, a mere fifteen thousand years for Lake Victoria to get its variety of cichlids is just a blink of time.  Yet they acknowledge that all these species appeared in this amazingly brief period.  Human skin color could have been selected in a similar short time: light skinned people who could make Vitamin D with less sunlight were selected for in northern latitudes, while dark skinned people who resisted the effects of intense sun were selected for in equatorial regions.
    Notice the sleight of mind with terminology in the last quote: “Divergent natural selection”, “parallel evolution”, “divergent selection”, “divergent natural selection”, and “divergent evolution” are used interchangeably to mean the same thing.  We are regularly being conditioned to confuse natural selection with evolution, or, to put it in other terms: micro-evolution with macro-evolution.  Evolution requires new information to be created.  There is no creation of new information here, as the articles admit.  In fact, one of the points the author makes is that the natural selection of the environmental factors often drove the frequency of a particular gene in a fish population to 100%.  All other genes affecting the characteristic had been eliminated.  This is loss of information, not gain – the opposite of what macro-evolution requires.  Surely, the scientists who wrote these papers must know this.  Once again, commitment to evolution is faith in spite of the evidence.
—DK

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