It would be helpful if, when discussing natural selection, evolutionists knew what they are talking about.
Many times articles promise insight into evolution but fail to deliver. That’s the case in a piece by Amro Zayed in Nature titled, “Evolution: Insect invasions and natural selection.” Zayed tantalizes his readers with visions of new species originating with wonderful new traits and functions that didn’t exist before. Isn’t that what Darwinism was about: the Origin of Species by means of natural selection, by which bacteria became humans? If natural selection is truly capable of such transformations, it should be evident in smaller cases like insect invasions. Here, though, is all that Zayed provides: a tale of bee genes.
In 2008, the authors identified only four different alleles at the csd gene, and they estimated that one out of four fertilized eggs would give rise to an inviable diploid male. However, a year later, the authors documented three additional csd alleles. Gloag et al. propose that these three alleles were so rare that they had escaped detection in 2008. The authors showed that the rare alleles were not the result of new mutations because the alleles’ DNA sequence was substantially different from those of the alleles found in 2008. It is also unlikely that these new A. cerana csd alleles were introduced by a secondary invasion, because the authors did not observe new alleles at the other DNA regions they examined. Rather, the presence of these three rare alleles in 2009 is best explained by balancing selection, in which bees that carried the rare csd alleles in 2008 contributed more offspring to the next generation.
What is balancing selection? Zayed relies on Gloag et al.‘s study in Nature Ecology & Evolutionto explain what was observed when one species of bee invaded another species’ habitat:
The authors speculated that a special form of natural selection, called balancing selection, would have a role in reducing imbalances in the frequency of csd alleles. This would, in turn, reduce the production of inviable diploid males in the invasive population. With balancing selection, individuals that have rare csd alleles would be expected to have high fitness because they would be unlikely to mate with an individual that had the same allele — a mating that would result in the production of diploid male offspring (Fig. 1). Carriers of rare alleles should contribute more offspring to future generations and increase the frequency of their initially rare csd alleles over time. A prediction about balancing selection on csd is that an equilibrium would be reached when all csd alleles have the same frequency.
Let’s take stock of the situation. Is this a demonstration of neo-Darwinian evolution in action?
- Did any new traits arise? No; both populations already had genes with “substantially different” alleles for this gene. All that changed were the relative numbers of the two types in the population. Notably, the authors state that the “rare” allele did not happen by new mutations.
- Did “fitness” increase? Well, how did they measure “fitness”? They fell into the tautology trap by equating it with reproduction (see “Fitness for Dummies,” 10/03/15). In other words, the successful bees did not have any new organs or improvements that made them stronger; they just left more eggs. More precisely, they left enough eggs not to go extinct in the new habitat.