An old Monty Python sketch about a mistranslated Hungarian-to-English phrasebook made infamous the line, “My hovercraft is full of eels.” Today, evolutionary biologists are puzzled about something equally bizarre: why are eels so full of speciation? One biologist recently said on ScienceDaily, “How can you have seven species of the same fish eating the same thing and, quite literally, living under the same rock?” Under evolutionary biology, one would expect to find some mechanism–perhaps a geographic barrier like a large expanse of open ocean–responsible for the reproductive isolation that generated the new “species.” Instead, they found this:
To find out the biologists looked at selected mitochondrial and nuclear genes and asked whether there were unique alleles (variants) of these genes and whether the degree of variance was correlated with geographic separation. They found lots of variation among the eel genes they examined, but virtually none of it had any geographic structure. In other words where the eel was living didn’t predict its genetic makeup.
“Some of the sampling sites are about 22,000 kilometers apart, so essentially two-thirds of the globe,” says Reece. “Yet you find the same alleles in South Africa as you do in Panama.”
“The only way to get shared genetic material across these distances,” says Reece, “is through gene flow.” The leptocephali [eel larvae], in other words, are efficiently ferrying genes from one population to the next, keeping the gene pool well stirred.
Several other reef fishes are also known to have highly dispersive pelagic stages. However, even these species show genetic partitions at major biogeographic barriers.
Under the most common definition of species (the biological species concept), a “species” is a natural population, or groups of natural populations, that inbreed and are reproductively isolated. While it wouldn’t be surprising if further work uncovers some mechanism which caused reproductive isolation in these eel populations, this whole episode raises a larger question: Just how significant is it to find evidence for “speciation”?
“Speciation” doesn’t necessarily imply evidence for the creative power of the Darwinian mechanism, for one can achieve reproductive isolation without undergoing any dramatic degree of biological change. In many cases, the differences between “species” can be very small, or even trivial. For example, many of these eel species have essentially identical body plans, niches and habitats, feeding habits, and many other traits such that their primary differences appear to be size, coloration patterns, occasional variations in ornamentation, and small genetic differences. But no matter how you slice it, they’re all eels.
If an evolutionist tells you to accept Darwinism because of evidence of “speciation,” be sure to find out exactly how much biological change is documented in said instance of “speciation.” In virtually all examples of speciation I learned about in school, the amount differences between the two species were trivial, and it was only unwarranted over-extrapolations from humble data which lent support to the grander claims of neo-Darwinian evolution that random mutation and natural selection can produce large-scale biological change.