Drifting fish or Selecting fish? The case of the threespine stickleback.

I don't know how Darwin would feel to learn that scientists today debate the tempo of evolution, and often use him as the straw man for gradualistic evolution. His idea for evolution came about as much from his trip on the Beagle around the world, as from talking to his neighborhood farmers in England. Those local farmers taught Darwin about artificial selection, and he just applied it to the natural world, and coined the now famous "natural selection" process. To invoke this process he needed to expand the amount of time natural selection had operated, and in the 1850's little was known of the age of the Earth. Today, with all that we know (the earth is 4.5 billion years old!) Darwin is still invoked as the feigned credo of evolution meant to be overthrown by new scientific methods. Yet the debate of the tempo of evolution is really a product of the twentieth century, and the genetic experiments carried out by the likes of Theodosius Dobzhanzky on the fruit fly Drosophila. Dobzhanzky found that in small populations, introduced genetic differences in an individual could come to dominate the population over time, without the process of any sort of selection. This observation is called genetic drift or neutral drift. When attending the Stony Brook University, I attended a course taught by three professors in the department of evolution and ecology. Each one had a slightly different view on which evolutionary process is found more in the natural world. Dr. Walter Eanes viewed evolution as operating primarily under the scope of drift, while Dr. Michael Bell viewed evolution as operating primarily under the scope of selection. The third professor was Dr. Douglas Futuyma who glued the two ideas together with an encyclopedic knowledge of evolution.

In the recent journal Paleobiology one of my old professors (Dr. Michael Bell), published a paper on threespine stickleback fossils, in an attempt to determine which mode of evolution operated on the number of spikes on sticklebacks persevered in the varves (annual layers) of a ten million year old lake. Alas, Dr. Bell was unable to prove that the decline in the number of spikes over time was a consequence of selection or drift. Concluding in the paper with the relinquishing statement-- "The longer the time intervals are between successive fossil samples, the more likely it is that the effects of directional selection will be obscured by random processes." I still am a believer that both processes operate in the natural world, and both are responsible for the diversity of life we now enjoy.

Bell MA, Travis MP, Blouw DM (2006) Inferring natural selection in a fossil threespine stickleback. Paleobiology: Vol. 32, No. 4 pp. 562–57