DNA mutation rates?

Vox Day has a couple new books out about how fast DNA can fix mutations. It’s based upon well-established science following the evolution of e. coli in the lab. These asexual bacteria split every half hour or so, so it’s fairly easy to track how many generations it takes for a captive population to fix a mutation. The answer, established by multiple experiments and just a touch of very simple math, is one mutation fixed per 1,600 generations. That includes parallel fixation, by the way.  (40,000 generations / 25 fixed mutations = 1,600 generations per fixed mutation on average.)

How many base pairs does e. coli bacteria DNA have? 4,639,221. Do the math, and that gives a fixed mutation rate of 7423 generations per million base pairs. Let’s call it 7,500.

So, let’s extrapolate that to a much more complex, multicellular creature - the cichlid fish of Lake Victoria. Their DNA has about a billion base pairs, and they breed sexually. Sexual reproduction doubles the chances of mutation in offspring (there being two parents, each of which may pass a mutation). So we have a sexual reproduction mutation fixation rate of 3750 generations per million base pairs.

Cichlids have a billion base pairs. That’s 1,000 million. So we expect a total of 3.75 fixed mutations per generation. Cichlids breed at two years of age. Lake Victoria has been an isolated breeding ground for at most 100,00 years. That’s 50,000 cichlid generations. 50,000 times 3.75 = 187,500 fixed mutations in that time. The average DNA spread between each of the over 400 different species of cichlids is about 750,000 base pairs. So there has been, at best, 1/4 the time needed to produce such biodiversity, given the DNA experiments with e. coli.

You’ll notice I have made no attempt to explain how 3.75 mutations would fix across an entire population in one generation. I’m just doing the math.

By the way - humans have a little over 3 billion base pairs. That would result in 11.25 fixed mutations per generation. (This obviously does not happen in modern humans.  We would have noticed.  But let’s ignore that simple observation.) There are 20 million mutations between humans and chimp common ancestry. That evolution happened in at most 9 million years. Assume one generation to be 20 years, and that’s 450,000 generations. Multiple by 11.25, and you get 5,062,500 fixed mutations. Again, one quarter of what’s necessary.

Does sexual reproduction result in a rate of beneficial (or at least neutral) mutation fixing at least 8 times faster than asexual reproduction?

(Vox's error is, in a computing metaphor, to assume that the number of cores working to parallel process information is irrelevant.  He assumes that 4 cores process the exact same amount of information as 3,000 cores.)