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Friday, October 10, 2008

Darwinism and popular culture: Fish story evolves in pop science media

British physicist David Tyler looks at a recent find in cichlid fish which has been vastly hyped as evidence for rapdi appearance of new species. He means hype like this Nature News story (1 October 2008), which proclaims "What you see is how you evolve: Differences in vision could give rise to new species."

Here's the abstract of the paper Tyler discusses:
Speciation through sensory drive in cichlid fish

Ole Seehausen, Yohey Terai, Isabel S. Magalhaes, Karen L. Carleton, Hillary D. J. Mrosso, Ryutaro Miyagi, Inke van der Sluijs, Maria V. Schneider, Martine E. Maan, Hidenori Tachida, Hiroo Imai & Norihiro Okada

Nature 455, 620-626 (2 October 2008) doi:10.1038/nature07285
Abstract: Theoretically, divergent selection on sensory systems can cause speciation through sensory drive. However, empirical evidence is rare and incomplete. Here we demonstrate sensory drive speciation within island populations of cichlid fish. We identify the ecological and molecular basis of divergent evolution in the cichlid visual system, demonstrate associated divergence in male colouration and female preferences, and show subsequent differentiation at neutral loci, indicating reproductive isolation. Evidence is replicated in several pairs of sympatric populations and species. Variation in the slope of the environmental gradients explains variation in the progress towards speciation: speciation occurs on all but the steepest gradients. This is the most complete demonstration so far of speciation through sensory drive without geographical isolation. Our results also provide a mechanistic explanation for the collapse of cichlid fish species diversity during the anthropogenic eutrophication of Lake Victoria.
He comments:
"The strongest evidence yet" involves a correlation between the visual system, body colour and ecology. Instead of this being used to support a hypothesis of sexual selection based on body colouration, the authors claim to have demonstrated sexual selection in action. This has been picked up by the media as fact: "a fish species in the cichlid family has been observed by scientists in the act of splitting into two distinct species in Lake Victoria" (Source). The cover of Nature proclaims that this is "a textbook example of evolution in action".

Let us suppose that the hypothesis is tested and confirmed, and the "sensory drive speciation" is validated. What are the implications for our understanding of evolution? It means that an ancestral fish population can split into two or more populations on the basis of colour. The daughter populations have differences in sensitivity to light frequencies and differences in body colouration. These may be accompanied by other ecological adaptations. There is no new genetic information - just fine-tuning of existing genetic systems. There is no evidence that these new species lack the potential to interbreed. Indeed, the differences are so slight that hybridisation to produce fertile offspring can be predicted with some confidence.
Talk about textbook examples - as the study authors themselves observe, for their particular proposed path, "empirical evidence is rare and incomplete." Now, to their delight, they have finally found an example (if the two schools of fish don't just interbreed back into hybrids after a few decades).

The problem isn't with the researchers, who sound suitably cautious. It's the pop science media that jump on something like this, inflating it far beyond what the current state of knowledge would justify. That wouldn't matter if they were just speculating about some celeb's bumpy tummy, but unfortunately, they help skew science textbook and science teaching. Tyler concludes,

The punchline: ID scientists are not opposed to the teaching of evolution in schools, but want it taught properly - allowing critical appraisal and the recognition of spin. Let speciation in cichlid fish enter the textbooks, not as a proof of evolution, but as an example of how evidence is brought to bear on current hypotheses of the origin of species.
That would be higher quality teaching, but would lead to too many embarrassing questions. My guess is, both the pop sci mags and the textbooks will stick to "proof of evolution" for the present.
Find out why there is an intelligent design controversy:

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