It really is the weirdest program. I can’t find a version history anywhere so I can see what changes were made and when.
This prompted me to once again download the latest version I could find. Re-confirming all my previous complaints that it is a trash piece of software for both reasons of theoretical evolutionary genetics, and practicality.
The program now seems to allow values much higher than previously without complaint, though it still contains vestiges of it’s earlier limitations, such as the pop-up that informs us what the previous allowed range of values was. That’s why I’d like to see a version history.
Anyway. First of all, why is there a field called “Total non-neutral mutation rate (per individual per generation”?
Shouldn’t the neutrality of a mutation be defined by the relationship between the mutation’s magnitude of effect and population size? Why isn’t it just called the “mutation rate” full stop?
Second, the maximum allowed reproductive rate (the maximum number of offspring produced by an individual) is 6. That’s ridiculous. How can you have predefined maximum of 6 and pretend it’s a realistic simulation for anything?
The memory limitations are obscene. It refuses to run with anything approaching realistic values. I have 32 GB of ram and yet it is literally impossible to run the software with realistic population values for things like bacteria and viruses, or innumerable eukaryote species. And the sorts of ranges that seem able to run (a few ten thousand at most) are not far from the zone where many species would be considered endangered anyway. The software therefore seems unable to run in anything but what could be considered a constant bottleneck mode. The very same area where conventional population genetics agrees there is a real danger of extinction due to selection being swamped by the power of drift. You can’t meaningfully simulate evolution for anything, even most eukaryote species have population sizes well above 25000 individuals.
That’s just a bit too convenient if you ask me.
Heritability is set at 0.2 by default. To my knowledge most mutations have a heritability of 1.0 unless they directly affect fertility in some way. This is Sanford doing an observable trait (such as height, a genetic multi-locus trait with a strong influence of environment) vs germline mutation bait-and-switch. Mutations are heritable, but their cumulative phenotypic effects, the TRAITS they result in, have other influences besides genetic, meaning offspring won’t inherit the exact height of their parents. This is Sanford lying with software. Or being incompetent. Take your pick.
Then there are the odd results you obtain if you run the simulation with whatever values you set. To really see how something must be wrong under the hood, so to speak, compare runs with two radically different values. For example, what would happen if 30% of all mutations were beneficial? Then compare it to more default values.
Here’s such a comparison. First some values (everything not specified here is left at default values). First run:
Total non-neutral mutation rate pr individual pr generation: 0.01
Beneficial to Deleterious ratio: 0.001 (1:1000)
Reproductive rate: 6
Population size: 10000
Generations: 1000
Functional genome size: 30E+04 (basically a virus genome)
Maximum beneficial fitness effect: 0.1
Allow back mutations?: Yes.
Heritability 1.0
Recombination model: Clonal reproduction
I’ll change the bolded number for the next run.
Results:
On the first figure we see deleterious mutations accumulate steadily, while beneficial mutations don’t. On the second figure mean population fitness remains constant. Weird. (The red line indicating fitness isn’t visible because it is exactly underneath the blue line).
Run two:
Beneficial to Deleterious ratio: 0.3 (3:7) So
30% of all mutations are now beneficial, where before it was one in one thousand mutations.
Results:
Hey good news, beneficial mutations now accumulate, though still slower than deleterious ones.
Wait, what? With 30% of mutations being beneficial, population fitness still doesn’t increase?