Does a Genetic Meltdown Cause a Population to Adapt?
by AITSE webmaster and ID expert Mario Lopez
As our readers know, AITSE is committed to help improve science education and encourage scientific integrity. And for those familiar with our Bunk Detecting Principles, it comes as no surprise that some scientists employ smoke and mirrors in an effort to validate certain claims. Here is a nice example of one such case.
In a recent paper entitled Evidence for elevated mutation rates in low-quality genotypes, authors Nathanial P. Sharp and Aneil F. Agrawal sneak in a gratuitous statement about the possible effects mutational load could have on the acceleration of adaptation into new environments. Interestingly, the paper is only intended to provide evidence for increased mutation rates in weak genotypes (using fruit flies), but the authors also propose that a mutational meltdown can result in adaptation:
The pattern we observe could also have positive effects on populations by increasing the rate of beneficial mutation in new environments. If novel environmental conditions increase the mutation rate by reducing individual quality through mismatch between genotype and environment, the resulting increase in genetic variance could accelerate adaptation.
Not only is this statement completely unsupported experimentally, the authors cited to support such a bold statement acknowledge that their own “experiments provide no evidence for or against a hypothesis of ‘adaptive mutation’.” Ignoring the more likely scenario that a genetic meltdown will result in a downward spiral towards extinction due to the preponderance of mortality rates over birth rates, the authors propose that beneficial mutations will somehow overcome the accumulation of irreversible deleterious mutations, leading to adaptation.
Indeed, the experimenter’s own mutation accumulation line maintenance, prior to conducting the fitness assay (i.e., the sampling of the population’s fitness), required the use of backups due to a “complete absence of offspring, suggesting male death or sterility.” This was required despite the fact that they employed a controlled experiment using serial backcrossing to manipulate genetic quality!
Can a population adapt during genetic meltdown? Well, if it can, Sharp and Agrawal certainly do not prove it; they don’t attempt to. Similarly I do not aim to refute the intended purpose of the authors’ work, but simply to point out that scientists can and often do make claims that are completely unsupported by their science. And AITSE is here to help you sort out the science from the bunk.
S. Goho & G. Bell, (d) Adaptive and Non-Adaptive Interpretations, 127-128
Freeman, Scott; Herron, Jon C (2007). Evolutionary Analysis, 4th edition. San Francisco: Benjamin Cummings. pp. 308-309.
W. Gabriel, M. Lynch, and R. Burger (1993). Muller’s Ratchet and mutational meltdowns. Evolution 47:1744-1757.