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9780226520438 Evolutionary process can be modeled in both genes and culture. The former is defined by vertical transmission, while the latter can be vertical and/or horizontal. Unlike heritable biological traits, cultural phenotypes have no discernible units of inheritance in a straightforward fashion which can be easily mapped. But some of the formal models common in evolutionary genetics are also utilized in social evolution and behavioral ecology.

One of the easiest aspects of culture to gain a comprehension of is language. Unlike other cultural phenomena, such as religion, language is clear and distinct. Many believe that in some way it is a deep biological competency, and in fact would put it outside of the domain culture altogether because of its unique role at the center of the propagation of cultural “memes.” A new paper in PNAS explores the correlations of language and genes and geography, A comparison of worldwide phonemic and genetic variation in human populations (open access!). In short, the authors find that the differences in transmission of genes and language result in differences in their patterns of distribution. The correlation between genes and geography scales over the whole world. The more distant a population is from a focal group of interest, the more genetically different it is. In contrast the signal of linguistic affinity (or lack thereof) exhibits spatial limits, beyond which the linear relation decays. Beyond 10,000 kilometers more distant languages are no more dissimilar.

bravo There are a few issues to unpack here. First, they used a database of phonemes. I have no idea how one would categorize differences using syntactic features, but it strikes me that someone without more familiarity with this field might argue that looking at variation in phonemes is a bit like looking for the key under the lamp. Interestingly the authors found that phoneme similarities transcend language family. In other words, nearness breeds familiarity through horizontal transmission even if the linguistic groups are dissimilar rather than being part of a dialect continuum.

Second, they suggest that one aspect of phonemes and how they differ from genes is that isolated populations exhibit more richness and diversity, rather than less. This illustrates that there are differences between genetic and cultural process. Not only is there a great deal of horizontal transmission, but cultural processes are subject to a greater “mutation” rate, and selection can be much more efficacious. The latter is why group level selection is more mathematically plausible for culture than genes; competing demes can be much more distinct in culture than genes because minimal gene flow can equilibrate biological differences, while biased transmission of culture can result in insulation of different groups from homogenization (e.g., inheriting your cultural traits from your father, rather than your mother, who may have been kidnapped from an enemy tribe).

Finally, in line with the high mutation rate of language the authors reject earlier findings that it follows the same serial founder model detected in a 2005 paper from some of the same authors. I have to jump in here to suggest that we need be careful about assuming that this paper is a robust result upon which we should build up our model. See Towards a new history and geography of human genes informed by ancient DNA for a slight revision. In any case, the results from the language patterns suggest that Europe is the source of human language, using the same framework as genes where there is a decay of diversity from the ancestral homeland. The authors point out that this is a artifact of the fact that phoneme richness is very low in Oceania and South America, and Europe is equally distant from both regions. In other words language is too protean to gain a signal of the “Out of Africa” movement. I do agree with this. It strikes me that those who attempt to reconstruct language as it was 50,000 years ago are grasping for straws. For example, I do not think that we can presume that clicks are ancestral just because the Khoisan have clicks in their language.

The relationship of patterns of genetic variation and cultural variation are essential to elucidate. That is because I believe that we can’t understand patterns of genetic variation without a clear grasp of the common cultural processes by which human genes propagated over time and space. Language is probably the cultural trait that’s lowest down on the tree, so hopefully researchers will keeping picking at it until the big questions get resolved.

 
• Category: Science • Tags: Genes, Language 
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There’s a variable in the GSS, GENEEXPS, which asks if genes play a role in personality. The options are:

- It’s genes which play a major role

- It’s experience which determines personality

First, let’s admit that the premise is stupid. Personality is heritable, but environmental variation also seems to matter. In other words it is noncontroversial to assert that both genes and environment can explain variation in personality (or perhaps more precisely genetic variation can only explain around half the variation for any given trait).

I was curious how this broke down by education and intelligence. To remove demographic confounds I limited the sample to non-Hispanic whites. For intelligence I used WORDSUM, with scores 0-4 being dumb, 5-7 being average, and 8-10 being smart.

Genes play major role Experience plays major role
Less than HS 33 67
High School 26 74
Junior College 26 75
Bachelor 21 79
Graduate 24 77
Dumb 25 75
Average 25 75
Smart 24 76
(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Behavior Genetics, Genes, Personality 
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A few people have inquired of the PNAS paper On sharing genes with friends. I avoided comment in part because I’m skeptical of the findings. So much behavior genomics just hasn’t panned out over the long term, and is probably susceptible to the issues which fuel the “decline effect”. Statistical significance is a random variable too. The fundamental issue which I want to emphasize is this: many behavioral traits are highly heritable, insofar as the correlation between relatives of trait value is in direct proportion to their genetic correlation. But, just because a trait is heritable does not mean that you can affix the variation to a specific set of genes. That is because the character of genetic architecture varies, and it may be that for many behavioral traits with some biological basis the causal variants which are responsible for the range in trait values are distributed across thousands of genes, and so are of very small effect.

Carl Zimmer relayed the depth of skepticism in the scientific community yesterday, and today Dr. Daniel MacArthur reviewed the paper. Here are the top line reactions:

Altshuler’s skeptical view of the paper was fairly widely shared by colleagues I discussed this with yesterday: given what we know about the genetics of complex traits, it seems a priori extremely unlikely to have found two real associations in a study of just six genes, even if those genes have been selected on the basis of biological plausibility. This seems especially unlikely for a behavioural trait: the complete failure of recent large genome-wide association studies to uncover any genetic variant convincingly associated with personality traits suggests that, while these traits are known to be strongly influenced by genetics, those influences are not exerted by common genetic variants of large effect.

The buzz amongst the genomics community on Twitter was generally similarly negative, although informed discussion wasn’t helped by the fact that (thanks to the standard ridiculous post-embargo delay from PNAS) the actual paper wasn’t available online until yesterday evening – meaning that there was little besides mainstream media reports for most people to base their judgement on.

So, what are we to make of the bold claims in this paper?

Overall I find myself rather torn here. While David Altshuler is absolutely right that this study wouldn’t meet the criteria for publication in Nature Genetics, and while I’m generally a fierce critic of both candidate gene association studies and behavioural genetics in general, there is more substance to this study than I expected. I’m not saying I’m confident the findings are real – that will require a full, independent replication study looking at exactly the same markers typed in this study – but it’s certainly a result that warrants follow-up.

So, where does this leave us? Not a great distance from where we started, really. This study is an intriguing observation in support of a broadly plausible hypothesis, and it’s entertaining to consider its implications for association studies, human evolution, and gene-environment interactions. However, until we see the promised large-scale GWAS, it’s best not to spend too much time pondering these implications: let’s save that for if and when we have the evidence needed to confirm that these effects are real, and to gain a better understanding of how common they are in the genome.

More broadly, fixing upon the most recent findings implicating a specific set of candidate gene(s), which only later turn out to be false paths poisons the bigger project of putting in proper perspective the biological component of human behavior. The heritability of many behavioral traits is is a robust finding. This truth often is unjustifiably put into the same category are “candidate gene for trait X.” When it comes to genetics and behavior there is the unfortunate reality that the stringency of the evidence needed to persuade is extremely conditional on normative preferences. Much of the media is hungry for genes for every ludicrous behavior (I am pretty sure that a fake press release on a “gene for skate boarding” could result in a series of articles all around the world), and, there is a broad acceptance in the public that behavior is substantially heritable. At the other extreme are those who are skeptical for normative reasons of universal tendencies in human behavior, or variation between sexes and groups. The same people who in other areas accept the provisional findings of “soft” sciences became as demanding as the most rigorous physicist when presented within findings which are not congenial to their preferred outcomes. Because of this consistent structural problem one must always tread with care and prudence when it comes to extraordinary claims.

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Behavior Genetics, Genes, Genetics, Genomics 
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Liberal Überblogger Matthew Yglesias, Pulling Back The Curtain on Human Behavior:

People sometimes seem to think that you could forestall a Gattaca-esque scenario of genetic transparency through privacy laws. But it seems to me that you’d actually need to go stronger, and not only guarantee the right to not have your genetic information disclosed. To prevent the emergence of a near-universal disclosure equilibrium in a world of cheap genetic profiling over the long run, you’d need to ban voluntary disclosure. The mere fact that you don’t want a potential partner to know your DRD4 profile will tell her all she needs to know about you.

800px-Galton_experimentLet’s grant the power of genomics to predict behavior in this way. Let’s also neglect the real problems of banning this sort of thing in a world of commoditized sequencing or typing.* I have some news for Matt & company, there’s already a much more powerful way to behavior genetic profile someone: look at their family. Indians have long known this. So the big short-medium term problem is that getting your hands on the biodata of anyone’s family members is one-click away….

Update: A commenter points out that Yglesias may have been advocating such a position to expose the absurdity of it. I wondered that too, but wasn’t sure and thought perhaps he was serious. In any case, I think the commenter makes good points, so I retract the charge. Though the bigger point obviously still stands.

* Unless Matt has Victorian values I assume he could anticipate that it wouldn’t be too hard to get “DNA” from a prospective partner. How exactly a ban would work when there are places overseas doing sequencing I have no idea. It isn’t as if biological material is never sent through the mail.

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Behavior, Behavior Genetics, Genes 
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Razib Khan
About Razib Khan

"I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. If you want to know more, see the links at http://www.razib.com"