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  Topic: Evolutionary Computation, Stuff that drives AEs nuts< Next Oldest | Next Newest >  
Bob O'H



Posts: 2564
Joined: Oct. 2005

(Permalink) Posted: June 18 2009,01:30   

Quote (Zachriel @ June 17 2009,19:39)
 
Relative fitness compares different genotypes in a population, and is defined as the ratio of the average numbers contributed to the next generation with one genotype set arbitarily at 1. So if genotype-A contributes 300 and normal genotype-B contributes 200, then genotype-A has a relative fitness of 1.5 compared to genotype-B. Relative fitness can be most any non-negative number.

Absolute fitness is calculated for a single genotype as simply the ratio of the numbers in the new generation to the old after selection. So if the population of the genotype increases from 100 to 200, then it has an absolute fitness of 2. Again, absolute fitness can be most any non-negative number.

Yes, this is how it's done.  Personally, I'd prefer it if it was on the log scale: there's all sorts of statistical theory that slots nicely into the evolutionary theory.

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I've been trying to independently implement Mendel's Accountant, but keep running into such definitional problems. Heritability. Fitness. And how they're handling probability selection. I'm working with a simplified model, but Mendel's Accountant should be able to handle the simple cases with obvious results.

My advice: keep away from heritability.  It complicates matters, and is dependent on the genetic variation in the population.  I suspect Sanford et al. don't really understand quantitative genetics: certainly Sanford makes some mistakes because of his lack of understanding in Genetic Entropy.

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I'm assuming that if fitness increases by 1, then it goes from 1 to 2 (100% increase), or from 2 to 3 (50%) and so on. It shouldn't be additive, but multiplicative so it scales. Sanford's complaint is that if we use multiplicative, then it can never reach zero. So he is clearly assuming his conclusion.


Indeed, but it can get arbitrarily close to 0, so it doesn't make any practical difference (unless you're working with continuous populations, when you end up with nano-foxes).

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It's not easy to resolve some of these problems. If we scale fecundity with fitness, then that solves the problem of very low fitness. But introduces a problem if the fitness levels climb so that we may be radically multiplying the reproductive rate.


Don't you just have to invoke density dependence?  I think this Darwin chap had some thoughts along those lines, after he read Malthus.

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Of course, "generation" is an abstraction, so it may represent an undefined breeding season. Frankly, the whole thing is an abstraction, so any strong claims about the specifics of biology are invalid anyway.

Depends on what species you're working on.  For things like butterflies, it's fine.  And, to be honest, the purpose of Mendel's Accountant is to make general statements about evolution, so this stuff is OK, as long as it's clear what the assumptions are.  A lot of the assumptions shouldn't have too big an effect on the robustness of the claims.

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It is fun to dip into the various threads to watch cluelessness at work in the hands of the confident exponent. - Soapy Sam (so say we all)

   
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