Sep 01 2009

Evolving Mice

Evolution deniers (and deniers in general) often support their denial with the baseless assertion that there is no evidence for evolution, or for some aspect of evolution, like natural selection. It’s easy to make this claim if you are just ignorant of the evidence, or don’t care about factual accuracy. More sophisticated deniers are well aware of the evidence, they just rationalize some trivial excuse to dismiss it.

It amazes me to this day that creationists can say with a straight face that there are no transitional fossils, when such fossil evidence is regularly pulled from the ground, and numerous dramatic examples (or at least their replicas) fill our museums. In a pinch they say, for example, that Archeopteryx is not a transitional species from dinosaur to bird, it’s just a bird that happened to have teeth, and a long tail, and claws, and lacked certain flight adaptations. Although at other times they might say it was just a dinosaur with feathers. This is denial by labeling.

There is also evidence for the ability of mutation and natural selection to produce adaptive changes in a population.  The most elegant and detailed of this kind of evidence is now the research of Richard Lenski, who followed thousands of generations of bacteria in the lab, showing how they made a series of mutations that resulted in their ability to thrive on citrate as a new food source. Answers in Genesis has a typically incoherent rationalization, based upon their own ignorance of evolutionary theory:

Many evolutionists state that the bacteria are experiencing “adaptive evolution.” However, this is not evolution but rather adaptation. Molecules-to-man evolution requires an increase in information and functional systems. Instead, these bacteria are likely experiencing a loss of information and functional systems as has been observed in other mutant bacteria in Lenski’s lab. While these changes are beneficial in the lab environment, they do not lead to a net gain that moves bacteria in an upward evolutionary direction.

I wonder how they conclude that they are “likely” experiencing a loss of information. They are just making this up. And, it’s not even relevant. You see the century-old misconceptions in this nonsense – that evolution must be constantly “upward”. Also we see the common denialist strategy of acknowledging evidence but then dismissing it because of what it is not. AIG admits this is evidence of adaptation, but it is not evidence of increased complexity. This is irrelevant on every level – evolution does not require an increase in complexity, and adaptation is a critical component of evolution.These bacteria put together three randomly occurring mutations in order to evolve a new trait that adapted them to a new environment.

Now scientists report on a new stunning example of random mutations spreading through a population as an adaptation to a new environment. Dr Catherine Linnen of Harvard University and colleagues studied a population of deer mice living in the sand dunes of Nebraska. Deer mice are normally dark colored for optimal camouflage against dark soil. However, the mice living in the sand dunes are sandy colored. This provided an excellent research opportunity, as the sand dunes are known to be a recent geological feature – about 8-15 thousand years old.

What this means is that within that time frame dark colored deer mice moved into the sand dunes and must have later developed their light sandy-colored coats. Further, light-colored coats is not a variety that already exists in the deer mice population. In some cases, a species may already contain the genetic diversity to adapt to a number of environments, and those variations that are most adaptive will simply predominate in each particular environment. But no new mutations or traits are required.

In this case, Linnen discovered that the light-colored fur was the result of a single gene, named Agouti, that first appeared in wild deer mice populations only 4,000 years ago, and then rapidly predominated in the sand dune population. Essentially, the mice had to wait for a light-colored mutation to appear at random, but once it did it was heavily selected for.

This is a very nice evolutionary story. It demonstrates the appearance of a new mutation providing raw material for natural selection.

And, of course, the evolution-deniers are already busy downplaying and butchering this new bit of science. One creation site writes:

New Scientist noted that the mutation consisted of a single amino acid deletion within one gene known to be responsible for coat color in many mammals.  So if natural selection did anything, it deleted something; it did not invent something new (certainly not a new protein or enzyme from scratch).  Calling it a “beneficial mutation,” therefore, seems a stretch.

Right – a deletion mutation has “deleted something”. This is an example of an irrelevant objection – point deletions are significant mutations, they change the resulting protein, and in this case the phenotype. Then they move the goalpost – mutations don’t count, only creating new proteins from scratch (btw – enzymes are proteins, so saying “protein or enzyme” is redundant).  Of course, none of this has anything to do with whether or not the mutation was beneficial – the researchers here demonstrated that it is.

And again we see the same old denialist strategy of denying a piece of evidence for what it is not, even though this is irrelevant to what it is. These deer mice are evidence that random mutations can crop up, provide a survival advantage, and predominate in a population – something creationists say is inherently unlikely. This is also not evidence for many aspects of evolution. No one piece of evidence is sufficient to establish all the various aspects of evolution – but creationists deny each piece of evidence in isolation partly by saying what it is not evidence for. But if you put it all together, we have a complete set of evidence for the evolution of life on earth through variation and natural selection.

The story of the sandy-colored deer mice can be added to the vast tapestry of evidence for organic evolution. It is one piece to a complex scientific puzzle, but it snaps into place quite nicely.

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