Zachriel
Posts: 2723
Joined: Sep. 2006
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When each child has more than a single mutation, then average fitness can decrease over time. Even though fitness is a relative term, this decreasing fitness can impact essential biological mechanisms.
If the genome is 3e8 bases in size (or any such large number) and there is an average of one mutation per child, then we expect that ~1/3 of the children will *not* have mutations. If each mother produces 6 children, then chances are that each new generation will include many individuals without mutations. (E.g. mice often have several litters of 4-10 pups.)
If we use truncated selection, heritability=1, mutations=1, seed=30, all else default, this is what we see.
It's interesting to see how the deleterious mutations ride along with the beneficial mutations until fixation before being weeded out.
In nature, we expect that if the mother produces enough children, then there should be sufficient healthy progeny to prevent genetic meltdown and to allow the positive ratcheting of beneficial mutations. We might also expect that species will tend to push the envelope with regard to mutational limitations. That means when near the margins small changes in parameters will allow it tip one way or the other. With slow reproducers, we can then expect various factors that mitigate the long-term evolutionary trajectory with regard to the accumulation of deleterious mutations. One such factor is sexual selection which is prevalent in nearly all taxa of interest.
We can reasonably show that selection of a wide number of parameters avoids mutational meltdown and we would expect life to evolve to explore the limits of these parameters. Hence, to claim that a simplified simulation such as Mendel's Accountant can disprove evolution is not justified.
We're still rather curious about the selection parameters,
Truncation
Unrestricted probability
Strict proportionality probability
Partial truncation
i.e. exactly what each selection criterion is doing.
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You never step on the same tard twice—for it's not the same tard and you're not the same person.
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