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Two of the models that Pepe alluded to are Mueller's Ratchet and Kondrashov's Hatchet. We know that sex is powerful because it persists despite the high cost.
by bhickey 11y ago
Two of the models that Pepe alluded to are Mueller's Ratchet and Kondrashov's Hatchet. We know that sex is powerful because it persists despite the high cost.
Mueller's model assumes that fitness decreases as a linear function of deleterious mutations. In simplified terms: Got n bad mutations? You're more likely to reproduce than someone with (n+1) bad mutations.
In an asexual population, individuals will have the set of mutations plus those acquired by mutation from their time of divergence. When you add sex to the mix (ha!), your population stops looking so flat. It introduces variance and selection culls the maladapted individuals. What's really cool about this, is you can model the deleterious mutations being driven out of the population.
Kondrashov's model is even more powerful. Basically, it says that there's some capacity for deleterious mutations. A couple of things wrong? Yeah, you'll reproduce. Too many? Well, you stepped off an mutational cliff and you aren't long for the world. This step function actually removes deleterious mutations from the population faster than Mueller.
The advantage of sex is obvious even on an individual basis. We all should have a chromosome that's "worse than average". When you mix and match them among your gametes, you'll end up with some non-viable gametes and some superstars. By failing fast, any parental investment can go toward offspring who are more likely themselves to be viable.
[For more information, check out Gillespie's Population Genetics]
- jballanc 11y ago1. Mueller's ratchet is still a hypothesis. A well supported hypothesis, but there are cases that it doesn't yet explain (Bdelloid rotifers, for example). 2. Even accepting the premise, it doesn't explain why sexual reproduction should be favored over asexual reproduction with occasional conjugation. 3. Even assuming that this mechanism is sufficient to explain the advantages of sexual reproduction, it still operates over a long time scale (i.e. long enough for enough deleterious mutations to accumulate in the asexual reproducing population). What this comment and the parent (and many of the others in this thread) fail to understand is that no one is debating that sexual reproduction is advantageous over long enough time scales. The question that the authors of the original paper are addressing is how sexual reproduction could be advantageous enough on a short enough time scale sufficient for those organisms to avoid being outcompeted by asexual organisms.
- bhickey 11y agoWhat this comment fails to understand is that I was explaining mathematical models for sexual reproduction to an audience who might otherwise be unfamiliar with it. Any inference that I was making claims about the relative efficacy of sex is sorely mistaken. Finally, this house would like to remind the honorable gentleman that he is invited to comport himself in a civil manner.
- jballanc 11y agoApologies and much appreciation for the introduction of some interesting, and very much important, models from evolutionary biology. I fear my tone was somewhat poisoned by that of the grandparent comment. Wanting to learn about evolution is fine. Doing so by asserting that certain accepted "truths" might not hold is also perfectly valid (assuming you're willing to accept when you are wrong). Claiming that the entire premise of a course of research, on which numerous scientists with extensive training have worked, is "false" is just filled with the worst sort of hubris.
- bhickey 11y agoNo worries. Leaving claims of hubris aside, I think some of the sibling threads are a tad mistaken. For example, population size is a determiner of the rate of neutral drift. I'm trying to work through what are the implications to having more genealogical ancestors than genetic ancestors, but it isn't immediately clear. If you really want your mind blown, check out Art Poon's paper "The Rate of Compensatory Mutation in the DNA Bacteriophage φX174" and Daniel Weinreich's "Darwinian evolution can follow only very few mutational paths to fitter proteins". Both have some amazing evolutionary implications.