And it’s not a serious one. An atheist named Eugine at Tree of Woe completely failed to comprehend any of the disproofs of parallel fixation and resorted to a withdrawn 2007 study in a futile attempt to salvage it.
Vox is wrong about parallel fixation. The post below has a good explanation. It’s telling that the example Vox gives for why parallel fixation doesn’t work involves the asexually reproducing e. coli, when the whole power of parallel fixation relies on genetic recombination.
First, that’s neither the example I gave for why parallel fixation doesn’t work nor are bacteria any component of my multiple cases against parallel fixation. Second, with regards to the square-root argument to which he’s appealing, here is why it can’t save parallel fixation:
- It requires truncation selection. The argument assumes you can cleanly eliminate “the lower half” of the population based on total mutational load. Real selection doesn’t work this way. Selection acts on phenotypes, not genotypes. Two individuals with identical mutation counts can have wildly different fitness depending on which mutations they carry and how those interact with environment.
- It assumes random mating. The sqrt(N) calculation depends on mutations being randomly distributed across individuals via random mating. But populations are structured, assortative mating occurs, and linkage disequilibrium means mutations aren’t independently distributed.
- It doesn’t address the fixation problem. Haldane’s limit isn’t about purging bad mutations, it is about the cost of substituting good ones. Each beneficial fixation still requires selective deaths to drive it to fixation.
- The sqrt(N) trick helps with mutational load, not with the speed of adaptation.
- Worden’s O(1) bits per generation. Yudkowsky doesn’t refute it. And O(1) bits per generation is exactly the the same as the Haldane-scale limit.
The square-root argument concerns purging deleterious mutations, not fixing beneficial ones. Two different problems. The parallel fixation problem remains wholly unaddressed.