razib | April 18, 2007A few days ago I posted about how overdominance, the fitness advantage of a heterozygote (an Aa genotype instead of an AA or aa genotype), can maintain polymorphism (genetic variation) within a population at a locus. Roughly, the equilibrium ratio between the two alleles is determined by their respective fitnesses in the homozygote state. For example, if AA & aa are of equal fitness and of lower fitness than the heterozygote then the final equilibrium frequencies will be 0.5.
Heterozygote advantage is intuitively comprehensible to many people, after all we've all heard of "hybrid vigor…
razib | April 18, 2007I have a review up over at my other weblog of the book The Fall of Rome: And the End of Civilization.
razib | April 17, 2007The Scientist has some good quotes in a article on the chimp positive selection story from yesterday:
The screen failed to find evidence for positive selection of two genes involved in brain development and cognition - ASPMM and Foxp2 - that studies have previously identified as positively selected genes in the human lineage. Zhang and Lahn agreed that the discrepancy likely results from differences in statistical power between the methods used in the current study and those used in previous work, which also incorporated polymorphism data.
Update: MIT Technology Review has more:
To Zhang's…
razib | April 16, 2007One of the classic ways to maintain genetic variation with a population is "overdominance," in short, a state where heterozygotes exhibit greater fitness than the homozygote genotypes. Imagine for example a locus, A, with two alleles, A1 & A2. Now, assume the fitness is distributed like so across the genotypes:
A1A1 = 0.75
A1A2 = 1.00
A2A2 = 0.75
In a random mating population the equilibrium genotypes given particular allele frequencies are described by the Hardy-Weinberg Equilibrium like so:
p2 + 2pq + q2
In a diallelic scenario q is by definition 1 - p, resulting in some algebraic…
razib | April 16, 2007The times has a mildly stupid article up, Chimps are ahead of humans in the great evolutionary race, which just goes to show that the people writing the headlines often have no comprehension skills, or just don't bother reading more than the first paragraph of a story. As confused as the article is it contradicts such a stark assertion. Here's the important point:
They found 154 human genes that showed evidence of the rapid positive selection that marks out adaptive traits, but 233 chimp genes with the same qualities.
Read the article with great caution, some of the sentences are very…
razib | April 16, 2007 You know a scientist has made it to the "big time" when they are given the opportunity to write to a general audience. Some thinkers, such as Richard Dawkins, have made their name via popularization. Others, such as E.O. Wilson, only became notable figures outside of academia after having established their reputation and stature within science. David Sloan Wilson has taken the latter path. Evolution for Everyone: How Darwin's Theory Can Change the Way We Think About Our Lives is an ambitious book, as the title should make clear. But just as E.O. Wilson's forays into popularization have…
razib | April 15, 2007...sorry about the delay this week. Been busy, will post a few more before next Friday.
razib | April 13, 2007I promised I'd go over the recent PNAS paper, Group selection and kin selection: Two concepts but one process. This is one of those articles where most of the heavy lifting is in the technical appendix. I've decided that it isn't worth the effort to restate this verbally in detail, I looked over the algebra and I didn't catch anything glaring (though I could have looked more closely), and would have felt ridiculous pointing out where they used "the chain rule here." The main point that I gathered from this paper is that Martin Nowak's model used groups which did not split very often, but…
razib | April 11, 2007I read Evolution for Everyone, and I was struck by how much David S. Wilson discussed religion. First, he seems to praise The Templeton Foundation quite a bit, in part because of their generous funding of his research. This isn't to say that he has any illusions about the nature of their interests, but he isn't an idealist about taking money to explore the questions which interest him. Wilson has to know that this is going to be come in for some scrutiny and no doubt some will denounce him for cavorting with the religious. That being said, Wilson is definitely not a Richard Dawkins style…
razib | April 11, 2007I don't normally blog about stuff like this, but I've decided to link to this story about an assault on a Sikh American veteran by a police officer. Here's the original story posted by the Sikh American Legal Defense and Education Fund. If this sort of stuff concerns you I encourage you to link as well, with a high enough pagerank some public pressure might ensue. Here's the relevant bit:
Mr. Nag then came outside to answer the officer's questions regarding the van. The Joliet police officer then demanded that Mr. Nag park the van inside his garage and not on the driveway, to which Mr. Nag…
razib | April 10, 2007A few months ago I was posting on R.A. Fisher's Genetical Theory of Natural Selection. I stopped because I was a bit confused as to what to do about the chapter on dominance, which was basically an exposition on a theory which has been falsified by the preponderance of data. In sum, R.A. Fisher contended that the dominance of an allele emerged via evolutionary processes, while his primary interlocutor Sewall Wright contended that this phenomenon was an emergent property of physiological dynamics. Fisher noted that "Wild Type" phenotypes are invariably dominant. He suggested that…
razib | April 9, 2007I'm not going to post about fr*ming (don't want this to get caught by the "Buzz" algorithm), just so you know. Yann pointed me to this paper, Group selection and kin selection: Two concepts but one process, and I'm going over the details (this is one where most of the math has been pushed to the appendix), but until I finish that, check out this....
razib | April 8, 2007Some people have joked that journalists have a tendency to always present "alternative viewpoints" even when the sides are not symmetrical in their cogency or credibility, e.g., "Earth is a sphere, views differ." That being said, this article about the controversy over blogging etiquette, and specifically the Kathy Sierra controversy really pisses me off because of this passage:
That may sound obvious, but many Internet veterans believe that blogs are part of a larger public sphere, and that deleting a visitor's comment amounts to an assault on their right to free speech. It is too early to…
razib | April 7, 2007I went to a Thai restaurant I frequent regularly today. The wait & kitchen staff know me, I called ahead to make sure they prepped "the usual," a medium rare steak served with onion, tomatoes and spicy lime sauce. In my case I like the lime sauce "4-stars spicy," that is, mixed together with a rich habanero paste. The first time I asked for this they gave me long lecture to make sure I could "handle it." No more. The chef is kind enough to rub the meat with the sauce before it's brought out me. When we showed up the server, who was new, told us the specials and took our wine orders…
razib | April 7, 2007A few days ago I introduced how higher levels of selection could occur via a "toy" example. Obviously it wasn't realistic, and as RPM pointed out a real population is not open ended in its growth potential. I simply wanted to allude to the seeds of how Simpson's Paradox might occur, where population structure is needed to explain overall trends. Now I'm going to dive into a somewhat more complicated model, one which Martin Nowak published last year in PNAS, Evolution of cooperation by multilevel selection. The paper is free, so if this post piques your interest I recommend you dive straight…
razib | April 7, 2007David Sloan Wilson, the doyen of Multilevel Selection theorists, has a new book out, Evolution for Everyone: How Darwin's Theory Can Change the Way We Think About Our Lives. It seems pretty clear to me that Wilson is trying to "do a Dennett" here. But unlike Dennett, who was not a scientist himself and so operated within standard evolutionary science by regurgitating Richard Dawkins' work (who was himself simply a channel for W.D. Hamilton and John Maynard Smith), Wilson is known to be something of a heterodox figure because of his emphasis upon higher levels of selection than the…
razib | April 5, 2007You know you've hit the big time when you are on CNN. Kind of like Anna Nicole.