July 24, 2008
The evolution of language and biology permlink
Category: Evolution
Sandman has a post up, Can There Be A Synthesis Between Cultural And Biological Evolution?, taking off on the PLoS Biology article, Across the Curious Parallel of Language and Species Evolution. Read both. I would add one important point though: linguistic and biological evolution are simply subsets of evolutionary dynamics. That is why Martin Nowak's book of that name, Evolutionary Dynamics, naturally has a section on the evolution of language. Several evolutionarily oriented thinkers have attempted to translate models originally developed for biology into the domain of culture. Cultural Transmission and Evolution and Culture and the Evolutionary Process are two works which I think are good introductions to the field.
Read on »
Posted by Razib at 12:18 AM•0 Comments
July 23, 2008
Drugs & science & insight permlink
Category: Culture
I posted before on Why scientists should do drugs (if they choose), via Tyler Cowen, a Jonah Lehrer article in The New Yorker:
Many stimulants, like caffeine, Adderall, and Ritalin, are taken to increase focus -- one recent poll found that nearly twenty percent of scientists and researchers regularly took prescription drugs to "enhance concentration" -- but, accordingly to Jung-Beeman and Kounios, drugs may actually make insights less like, by sharpening the spotlight of attention and discouraging mental rambles. Concentration, it seems, comes with the hidden cost of diminished creativity. "There's a good reason Google puts Ping-Pong tables in their headquarters," Kounios said. "I you want to encourage insights, then you've got to also encourage people to relax." Jung-Beeman's latest paper investigates why people who are in a good mood are so much better at solving insight puzzles. (On average, they solve nearly twenty percent more C.R.A. problems.)
In other words, what may make a more efficient engineer may also dampen creativity in a theoretical physicist....
Posted by Razib at 2:06 PM•4 Comments
Populism & public religion permlink
Category: Religion
Half Sigma points me to The Legend of a Heretic, which chronicles the close relationship between Robert G. Ingersoll, a prominent American agnostic of the 19th century, and the Republican Party elite of that time. It seems ironic that though we are a nation which explicitly bans formal religious tests, we live at a time where an implicit religious test exists. This despite the fact that Andrew Jackson was probably the first of our presidents who would be considered an orthodox Christian. But even as late as 1908 a Unitarian, William Howard Taft, was president (despite some grumblings about his unorthodox Christianity).
Read on »
Posted by Razib at 12:37 AM•3 Comments
July 21, 2008
The Dark Knight permlink
Category: Culture
I didn't watch The Dark Knight this weekend. Anyone else out there?
Posted by Razib at 5:51 AM•8 Comments
July 20, 2008
Why does race matter for women? permlink
Category: Culture
One social science finding which I've wondered about over the past few years is the result that women care much more about the race of a potential mate than men do. The fact that individuals tend to want to mate assortatively with those who share their characteristics is no surprise. Rather, what does surprise are a series of papers that show a very strong asymmetry in strength of preference between males and females. To be crass about it, an attractive warm body will do for a man, but women strongly prefer a body with the packaging of their own race!
First, let's keep this in perspective, here are the correlations from the GSS for married individuals for several variables of note (I've filtered for whites here):
Ethnicity - 0.40
Highest Degree - 0.55
Socioeconomic index - 0.32
I think it's interesting to note that the variable which reveals meritocratic achievement has the highest correlation. Ethnicity is something you're born into, and socioeconomic index is a metric which derives from the milieu in which you were raised.
This post is going to review some findings in a paper which attempts to both describe the differences in race preference for dating by race and across genders, and, why those differences might emerge the way that they do. The paper is Racial Preferences in Dating, Review of Economic Studies (click the link to download and read the whole thing yourself!). Here's the abstract:
We examine racial preferences in dating. We employ a Speed Dating experiment that allows us to directly observe individual decisions and thus infer whose preferences lead to racial segregation in romantic relationships. Females exhibit stronger racial preferences than males. The richness of our data further allows us to identify many determinants of same-race preferences. Subjects' backgrounds, including the racial composition of the ZIP code where a subject grew up and the prevailing racial attitudes in a subject's state or country of origin, strongly influence same-race preferences. Older subjects and more physically attractive subjects exhibit weaker same-race preferences.
A few points need to be made clear: males do not exhibit statistically significant racial preferences by and large. That's somewhat shocking to me. I'm not surprised that older subjects have weaker biases, I suspect frankly they're more realistic and don't want to narrow their options anymore than they have to. Finally, I'm totally confused as to why hotties would be less race conscious; you would figure if hybrid vigor is real that the marginal returns would be greatest for the fuglies (specifically, assuming that fugitude correlates with individual mutational load and hybridization would be better at masking that load). But the most relevant demographic point is that these are Columbia University graduate students. In other words, a cognitively & socially elite sample.
Read on »
Posted by Razib at 3:50 PM•48 Comments
HIV may not be associated to Duffy!?!?! permlink
Category: Genetics
Over the past few days I've blogged a bit about the story about an HIV susceptibility allele; Evolution, a reason for the African HIV epidemic?, Overplaying "AIDS genes" and HIV susceptibility, a "black" thing, not a Duffy thing?. But there's an important post Genetic Future, Duffy-HIV association: an odd choice of ancestry markers:
In the Duffy study the authors attempt to perform this type of correction using a set of just 11 markers they describe as "differentially distributed between European and African populations". p-ter notes that several of these markers are not particularly ancestry-informative, and indeed on closer inspection it's clear why this is: these genes weren't originally selected on the basis of ancestry informativeness, but rather because they are associated with HIV biology. Every single one of the 11 markers has some association with HIV: three of them have previously been associated with HIV infection, progression, or response to treatment (CCR5 delta32, APOBEC3G H186R, GNB3 C825T); most of the remaining markers are in genes that are known binding targets or modulators of HIV (CCR5, CXCR4, PD1, TRIM5, IL-2, IL-4).
...
If that's true - and it's difficult to see any other rationale for using these HIV markers rather than a set of validated AIMs - this is poor form for at least two reasons. Firstly, it's unlikely that using such a weak set of ancestry-informative markers provides an effective correction for a marker with as strong a correlation with ancestry as Duffy (as p-ter notes, all of the supposed ancestry markers are far weaker predictors of ancestry than the Duffy variant). Secondly, testing several different variants for an association with HIV and then only reporting the one that achieved significance creates the perfect conditions for a false positive due to multiple comparisons - it's entirely possible that the Duffy association would not have survived correction for multiple testing. It's difficult to assess this fully because the manuscript doesn't seem to report a single P value (!), although I note that the lower edge of the 95% confidence interval of the odds ratio in Figure 2C is perilously close to 1 following their ancestry "correction".
Read the whole thing...but something is starting to smell fishy. Hey Dave Appell, blogs rock and peer review sucks! (sometimes)
Posted by Razib at 2:38 AM•0 Comments
July 19, 2008
Viability selection and genetic screening permlink
Category: Genetics
Just a quick follow up to my post about genetic screening of embryos and subsequent implantation. The spontaneous abortion rate for humans is very high. Probably on the order of 50% of fertilized ova implant and complete to term. I've seen numbers all over the place. In any case, I assume many of these are chromosomal abnormalities. But I've also posted to data which strongly suggests that immunological incompatibilities between mother & fetus also play a role in spontaneous abortions and may result in natural selection which we're not too well aware of. In The Cooperative Gene the evolutionary biologist Mark Ridley suggests that because of spontaneous abortion we should be less than worried about reduced efficacy of natural selection in purging deleterious alleles from the gene pool; as the genetically unfit reach viability and reproduce their alleles will be culled at the stage of of the embryo and fetus.
Read on »
Posted by Razib at 10:05 PM•2 Comments
HIV susceptibility, a "black" thing, not a Duffy thing? permlink
Category: Genetics
DARC and HIV: a false positive due to population structure?:
The authors are aware of this potential confounder, and develop a measure of admixture based on 11 SNPs to include as a covariate in their regression. However, this measure is kind of weak, which I imagine in the sticking point for the skeptics in the Times article. If you have access to the supplemental information, take a look at it--several of these 11 SNPs are in the same gene, which means they're not independent, and several don't even have big frequency differences between African and European samples (if you're trying to judge via SNPs whether someone is more African or European, those SNPs better have a big frequency difference between Africa and Europe). This is probably not a precise measure of ancestry. In fact, the Duffy null allele they claim as associated is a better predictor of ancestry than any of these SNPs.
So it's quite possible that the authors have simply shown a correlation between level of African ancestry and susceptibility to HIV (which could be due to any number of sociological, demographic, or genetic factors), rather than an association between Duffy null and susceptibility to HIV. Here's a relatively simple test of this possibility: genotype rs1426654 (the nonsynonymous SNP in SLC24A5) in their sample and perform exactly the same test as performed with Duffy. The motivation for this is that this SNP shares the property of Duffy null of being highly informative about ancestry, while being in a gene that presumably plays no role in HIV infection. If you get an association there, it seriously calls the Duffy result into question; if not, you feel a bit more comfortable.
This is why mapping human variation is so important. Note that the genetic variation itself might not even be responsible for greater susceptibility to HIV in a causal sense; if circumcision does have a role in reducing the spread of HIV then cultural practices which correlate with genetic variation can also produce spurious correlations. As an illustrative example in South Africa there is a correlation between HIV infection rates and decreased Khoisan ancestry. I say this because the Zulus have higher infection rates than the Xhosa, and the latter have a great deal more Khoisan ancestry than the former. The differences have been attributed to the fact that the Xhosa practice circumcision and the Zulu do not, so the differences in genes is just coincidental.
Posted by Razib at 2:20 PM•1 Comments
July 18, 2008
The Perfect BabyTM permlink
Category: Genetics
Genetic Future points me to a Nature News story, Making babies: the next 30 years. He highlights this section:
There's speculation that people will have designer babies, but I don't think the data are there to support that. The spectre of people wanting the perfect child is based on a false premise. No single gene predicts blondness or thinness or height or whatever the 'perfect baby' looks like. You might find genetic contributors but there are so many environmental factors too.
The details are important here. Height is a tough cookie; it seems like there are going to at least hundreds of loci which control most of the normal human variation (if not thousands). But blondness is a bad example; pigmentation is only controlled by a few loci. Getting a fix on OCA2, SLC45A2, SLC24A5 and KITLG will get you what you want. That doesn't mean the parents don't have to have the variation necessary, they do, but they can probably guarantee a little blonde beast if they have the potentiality. And it seems that this really isn't a function of the genetic future, the number of embryos parents would need to guarantee a little Aryan baby if they both have Aryan blood isn't that high (probably 10-100 embryos depending on the purity of Aryan blood of the parents).
In any case, read the Genetic Future post for the bigger picture.
Posted by Razib at 8:12 PM•6 Comments
R. A. Fisher and Epistasis permlink
Category: Evolution
David takes a slight detour in this Sewall Wright, series, R. A. Fisher and Epistasis:
My next note on Sewall Wright will cover the exciting subject of the adaptive landscape. As every schoolboy knows, Wright considered epistatic gene interactions very important in determining the 'peaks' of the landscape. A sharp contrast is sometimes drawn between Wright and R. A. Fisher in this respect....
This is a preamble to a very long and dense post. If it interests you in the subject, I'd also recommend Epistasis and the Evolutionary Process. You might also check out this older post of mine on evolutionary epistasis.
Related: Notes on Sewall Wright: Population Size, Notes on Sewall Wright: the Measurement of Kinship, Notes on Sewall Wright: Path Analysis, On Reading Wright and Notes on Sewall Wright: Migration.
Posted by Razib at 1:34 PM•0 Comments
Black and white twins & perils of Colored admixture permlink
Category: Genetics
I was curious why an old Genetics and Health post, Twins with Different Skin Color Genes, was sending me many referrals today. Now I know, Two in a Million: Twins Born - One Black, One White:
The twin boys, named Ryan and Leo, are the offspring of a mixed-race couple.
The mother, Florence, hails from Ghana in western Africa, and dad, Stephan, is from Potsdam in Germany.
"Ryan came first, and everything was as usual," said the hospital's doctor, Birgit Weber. "But when Leo was born, I couldn't believe my eyes."
"Both kids have definitely the same father," the doctor added.
These aren't the first of these "amazing" of twins. I've posted on this sort of story before, Can you tell if you're black or white?, "Black" & white twins again and Ivory & ebony, twins again...and again.... I touched on the major genetic points in depth in those posts, but this case is a bit different since you have two parents who are monoracial; this makes the odds in terms of genotypic combinations a bit confusing. I think that the easiest way to explain the outcomes are stochasticity of gene expression during development, and, possibly gene-gene interactions between these two parents which allow for deviations outside of the expected range. If what I'm saying is unintelligible to you, I recommend you read the posts I linked to above, it will make the context clearer.
Read on »
Posted by Razib at 3:26 AM•32 Comments
July 17, 2008
Down with Darwinism! permlink
Category: Evolution
I agree with all the other ScienceBlogs that Olivia Judson is right. Do we talk about Newtonism? Einsteinism? We do talk about Epicureanism, Platonism, Neo-Platonism, Aristotelianism, etc. I think that says it all....
Posted by Razib at 4:25 PM•20 Comments
Overplaying "AIDS genes" permlink
Category: Genetics
Brandom Keim at Wired says Genes Don't Explain African AIDS Epidemic:
Seen in the wrong light, the numbers could present Africa's AIDS tragedy as a biological inevitability. Several press accounts do exactly that. The New York Times credits the mutation for "explaining why the disease is more common there than expected." Reuters says it could "help explain why AIDS has hit Africa harder than all other parts of the world," as this can't be fully rooted in "sexual behavior and other social factors." The Guardian says it "may go some way" to explaining the African prevalence of AIDS. And the Gene Expression blog titles its coverage, "Evolution, a reason for the African HIV epidemic?"
My first reaction was, "who would be retarded enough to think that one genetic difference entails inevitability?" But on second thought, that's just me being unreflective, many people are that stupid. In any case, I specifically titled my post "a reason" to highlight that the variation on the DARC locus might be able to account for some of the between population differences. It is true that most people aren't used to thinking of a dependent variable which is the outcome of the joint effects of multiple independent variables; that's why the genetic determinism straw-man is so easy to construct. Extrapolating from the study sample and the known nature of the polymorphism on the DARC locus, one could account for around 10% of the difference in HIV infection rates when it came to Duffy negative vs. Duffy positive populations. That's a big impact. In height or IQ the quantitative trait loci, the genes which effect variation, are on the order of 1% or less in effect. Something similar to the polymorphism on the DARC locus would be the skin color genes, the largest few effects being on the order of 10-40%.
Read on »
Posted by Razib at 1:32 PM•1 Comments
July 16, 2008
Evolution, a reason for the African HIV epidemic? permlink
Category: Science
Please read: Follow up post.
Genetic Variation Increases HIV Risk In Africans:
A genetic variation which evolved to protect people of African descent against malaria has now been shown to increase their susceptibility to HIV infection by up to 40 per cent, according to new research. Conversely, the same variation also appears to prolong survival of those infected with HIV by approximately two years.
...
HIV affects 25 million people in sub-Saharan Africa today, an HIV burden greater than any other region of the world. Around 90 per cent of people in Africa carry the genetic variation, meaning that it may be responsible for an estimated 11 per cent of the HIV burden there. The authors observe that sexual behaviour and other social factors do not fully explain the large discrepancy in HIV prevalence in populations around the world, which is why genetic factors are a vital field of study.
Read on »
Posted by Razib at 11:20 PM•5 Comments
July 15, 2008
A request permlink
Category: Blog
From Chris of Mixing Memory.
Posted by Razib at 11:14 PM•
