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Hybrid Sharks: From the Annals of Overselling Evolution

David Klinghoffer

In science news that touches on evolution, we’re perpetually being reassured that evidence of Darwinian theory’s fantastic explanatory power continues to pour in. Scanning this material, I often feel like John Cleese in the Monty Python “Pet Shop” skit. You know the one where the fellow bought a Norwegian blue parrot but brought it home and found it to be “stone dead” and nailed to the perch. When he goes back to the pet shop to complain, the shop owner (Michael Palin) tries pathetically to convince him the bird isn’t dead at all but merely “resting.” At one point Palin knocks the cage.
“There, he moved!”
“No, he didn’t, that was you pushing the cage!”
In this spirit, there comes now the excited news about a shark hybrid off the Australian coast, 57 specimens in all, the product of a union between two pretty much identical parent species, the common and Australian black-tip sharks. “This is evolution in action,” exultant researcher Jess Morgan of the University of Queensland told Agence France-Presse in a story picked up around the world.
Reporting in Conservation Genetics, the team of scientists explained:

Two black-tip whaler shark species (Australian, Carcharhinus tilstoni; Common, C. limbatus) have overlapping distributions in Australia, distinct mitochondrial DNA sequence (ND4, COI, control region) and distinct morphological features such as length at sexual maturity, length at birth and number of vertebrae. A mismatch was observed between species identification using mtDNA sequence and species identification using morphological characters. To test whether hybridisation between the two species was responsible, a nuclear gene with species-specific mutations was sequenced. Extensive interspecies hybridisation was found to be occurring. Hybrids were found from five locations on the eastern Australian coastline, spanning 2,000 km.

So what we have is two nearly identical shark species joining for whatever reason — climate change, according to one sexy explanation — to form a third likewise identical hybrid. What’s really happened is an another illustration of the principle that no one disputes, and can hardly be said to merit media coverage: The more things change, the more they stay — pretty much — the same.
There would be no cause for complaint about advertising this as evidence of “evolution” were it not for the fact that the word has as one common meaning — the only meaning that generates public interest and debate — a process capable of generating really impressive morphological novelty. Which this is not. The black-tip shark story is just more knocking the parrot’s cage.