May 15, 2008 - It's not evolution

An article in today's Seattle Times gives credit to evolution for a quick change in the kinds of stickleback fish in Lake Washington. However, that is not so clear.

Half a century ago, Lake Washington was very polluted and murky. It has since been cleaned-up, and its waters today are clear and swimmable. Natural selection pressures on the native stickleback fish therefore would have changed as well. Sticklebacks now have a much more difficult time hiding from their primary predator, cutthroat trout.

The stickleback is an unusual fish, in that it doesn't have scales. Instead the fish has bony armor plating. Certain types of the fish are completely covered in armor. However, there is a lot of variety in this feature, and other sticklebacks have less plating, or none at all.

They are also a very mobile fish, living in both fresh and salt water. In the case of Lake Washington, it is connected to the Puget Sound by the Chittenden locks instead of an outlet stream, so marine organisms can and do pass both ways. The salt-water sticklebacks characteristically have more armor covering.

In the 1960s, almost all of the Lake Washington sticklebacks were un-armored. But now, most of them are the armored variety. The explanation given in the Times is higher trout predation in today's Lake Washington, and a high quantity of genetic variation in stickleback populations. In addition, the two local (fresh & salt water) fish populations are blended as well.

When natural selection pressures changed after the clean-up, another combination of genes in the pool was already available to produce fish that were better adapted. This other pre-existing set thrived, and became dominant without any new species or new gene information content. However, evolutionary biologists use evolution as an umbrella term for all biological change over time. This conveniently lumps these stickleback changes with Darwinian evolution even though they are different processes.

The Seattle Times article exclusively credited evolution with the change. However, the Times' source article tells a more complete story. That, with my additional research showed me that this change was biologically just ordinary variation within a kind.

In fact, the sensationalization of the story is like that of the peppered moth. This species experienced a change in its dominant color during industrial revolution, and then again afterwards. At one time it was used as a prime example of evolution in action. Now, it is only useful for illustrating natural selection to laypeople (even though it is often told as if it had its old glory). I see this stickleback story as equivalent.

To me it is ironic that the Wikipedia article about the peppered moth story has "change in the frequency of an allele within a gene pool" as the definition for evolution. Using this definition does support the peppered moth changes as being called evolution. However, since this definition says a gene pool must exist, there is no room for a naturalistic origin for life. And also, since more than alleles separates many species we know today, Darwinian species evolution is also outside this definition.

So, like the peppered moth, the stickleback is a great story. But in the end, it is only an illustration of common biological adaptation, not Darwinian evolution.