friendship and natural selection (and human biodiversity)

i linked to this paper…

Friendship and Natural Selection

…in this past sunday’s linkfest, but, to be honest with you, i hadn’t actually read it. (yeah, i do that sometimes. ok, ok — a LOT of times!)

since then, a couple of people urged me to read the arXiv blogpost on it (thanks @DKshad0w and @SamoBurja!), which prompted me to read the orig. research paper and … wow! … mind. blown.

now, no, i’m NOT a geneticist — i don’t even play one on the innerwebs — so i’m not your gal for evaluating whether or not these guys — nicholas christakis and james fowler — have done their work right, but if they have, this is very cool stuff:

Pairs of friends are, on average, as genetically similar to one another as fourth cousins, which seems noteworthy since this estimate is net of mean ancestry and background relatedness.”

fourth cousins! note that these are (i believe) all white folks. the data are from the framingham heart study, but the researchers do say that they controlled both for relatives (i.e. that individuals might be “friends” with people who are, in fact, distant relatives) and ethnicity (eg. that italians might just be friends with other italians).

It is intriguing that genetic structure in human populations may result not only from the formation of reproductive unions, but also from the formation of friendship unions. This in turn has relevance for the idea of an evocative gene-environment correlation, proposed more than 30 years ago, which suggests that a person’s genes can lead one to seek out circumstances that are compatible with one’s genotype. Our results suggest that these circumstances could include not only the physical environment but also the *social* environment, and hence the genotypic constitution of one’s friends. As Tooby and Cosmides argue, ‘not only do individual humans have different reproductive values that can be estimated based on various cues they manifest, but they also have different association values.’ People may seek out particular, convivial social environments that affect their fitness.

i’ve been saying for a while now that the family types/social structures in which individuals are located ought to be taken into consideration when thinking about the fitness of those individuals and how natural selection might be working on different individuals living and reproducing in different sorts of social structures (individuals living in nuclear family structures versus large clan structures, for instance). i’ve mostly been thinking about family structures, but christakis and fowler are talking about friendship structures — alliances with non-family members. cool!

“The existence of excess genetic similarity between friends is also relevant to the growing area of indirect genetic effects, wherein the phenotypic traits of focal individuals are influenced by the genomes of their neighbors, in a kind of ‘network epistasis.’ In fact, our results support the idea that humans might be seen as metagenomic not just with respect to the microbes within them, but also with respect to the humans around them. It may be useful to view a person’s genetic landscape as a summation of the genes within the individual and within the people surrounding the individual, just as in certain other organisms.

yeah. just muse on THAT for a while. (~_^) and then try this on for size…

“[T]he human evolutionary environment is not limited to the physical environment (sunshine, altitude) or biological environment (predators, pathogens), but also includes the social environment, which may itself be an evolutionary force. Our finding that positively correlated genotypes are under positive selection suggests that the genes of other people might modify the fitness advantages of one’s own genes, thus affecting the speed and outcome of evolution.

did you get that? the researchers found that, the SNPs that were most common between the friends (the homophilic SNPs), have, indeed, been under recent positive selection:

“To test the hypothesis that homophilic SNPs are generally under recent positive selection, we use the Composite of Multiple Signals (CMS) score. This score combines signals from several measures of positive selection to create a single value that indicates the likelihood a SNP has been increasing in frequency due to selection pressure over the last 30,000 years (see SI). In Fig.3, we show that, after correcting for correlated outcomes due to linkage disequilibrium and for varying precision in the GWAS estimates (see SI), the top 20% most homophilic SNPs have significantly higher CMS scores than the other 80% (+0.07, SE 0.02, p = 0.003)…. In contrast, Fig.3 also shows that CMS scores are not significantly higher for the most homophilic SNPs in the strangers GWAS (–0.00, SE 0.02, p = 0.86). This suggests that the whole-genome regression model we use does not generate false positives…. In sum, it appears that, overall, across the whole genome, the genotypes humans tend to share in common with their friends are more likely to be under recent natural selection than other genotypes.

friendship and natural selection 01

friendship and natural selection 02
_____

with human biodiversity in mind, my question would be: do all peoples everywhere form an equal number of friendships with (technically) unrelated individuals? yes, i have an obsession with clannish peoples — but, seriously — do people who live in clans or tribes make as many “friends” as peoples who don’t? do they even have the opportunity? if not, what might this mean for natural selection in those populations?

(note: comments do not require an email. friends.)

inbreeding and cognitive ability among whites in the u.k.

via dienekes via jayman:

Genome-wide estimates of inbreeding in unrelated individuals and their association with cognitive ability

“INTRODUCTION

“Research on consanguineous marriages, and other forms of inbreeding, has long shown a reduction in cognitive abilities in the offspring of such unions. The presumed mechanism is that detrimental recessive mutations are more likely to be identical by descent in the offspring of such unions and so have a greater chance of being expressed. To date, research on the relationship between inbreeding and cognitive ability has largely been restricted to recent inbreeding events as determined by pedigree…. It has been suggested that intellectual disability is under negative selection, and that recent deleterious mutations have an important role in the underlying aetiology. The wealth of molecular genetic data currently available allows estimates of inbreeding on a genome-wide level and to examine the effects of long-term ancestral levels of inbreeding. Such an association with inbreeding, as measured by runs of homozygous polymorphisms (ROH), has previously been identified with several behavioural traits, such as schizophreniz, Parkinson’s disease and personality measures, as well as non-behavioural traits such as height.

“The relationship between inbreeding on a population level and cognitive ability is particularly interesting due to assortative mating, non-random mating, which is greater for cognitive ability than for other behavioural traits, as well as physical traits such as height and weight. Positive assortative mating has been reported for cognitive ability, particularly for verbal traits, with spousal correlations generally around 0.5. Assortative mating should lead to greater genetic similarity between mates at causal loci for cognitive ability and to a lesser extent across the genome, which in turn reduces heterozygosity at these local. In other words, in contrast to the genome-wide reduction of heterozygosity caused by inbreeding, the reduction of heterozygosity due to assortative mating for a trait is limited to loci associated with the trait…. Another difference between inbreeding and assortative mating is that the effects of inbreeding are expected to be negative, lowering cognitive ability, whereas the effects of assortative mating affect the high, as well as the low end of the ability distribution, thus increasing genetic bariance, that is, when high-ability parents mate assortatively, their children are more likely to be homozygous for variants for high ability, just as offspring of low-ability parents are more likely to be homozygous for variants for low ability….

“MATERIALS AND METHODS

“Participants

“The Twins Early Development Study (TEDS) recruited over 11 000 families of twins born within England and Wales between 1994 and 1996…. In this analysis, individuals were excluded if they reported severe current medical problems, as well as children who had suffered severe problems at birth or whose mothers had suffered severe problems during pregnancy. Twins whose zygosity was unknown or uncertain or whose first language was not English were also excluded. Finally, analysis was restricted to twins whose parents reported their ethnicity as ‘white’….

“Cognitive measures

“Verbal and non-verbal tests were administered using web-based testing. The verbal tests consisted the Similarities subtest and the Vocabulary subtests from the Wechsler Intelligence Scale for children (WISC-III-UK). The non-verbal tests were the Picture Completion subtest from the WISC-III-UK and Conceptual Grouping from the McCarthy Scales of Children’s Abilities. A general score was derived from the test battery as the standardized sum of the standardized subtest scores, which correlates 0.99 with a score derived as the first principle component of the test battery score.

“Runs of homozygosity

“FROH was defined as the percentage of an individual’s genome consisted of runs of homozygosity (ROH)…. [O]nly ROH with a minimum of 65 consecutive SNPs covering 2.3Mb were used when calculating the total proportion of the genome covered by ROH. In addition, the required minimum density in a ROH was set at 200kb per SNP, and the maximum gap between two consecutive homozygous SNPs was set at 500kb….

“RESULTS

“Table 1 includes descriptive statistics for FROH and the three measures of cognitive ability (general, verbal, and non-verbal). FROH is slightly positively skewed, as it represents the total percentage of the genome that includes runs of homozygosity (ROH). The average percentage of genome covered by ROH was 0.7% (95% CI 0.65-0.72%). Verbal and non-verbal abilities correlate 0.49; because general cognitive ability is the sum of the standardized verbal and non-verbal subtests, they correlate much more highly with general ability (0.87 and 0.86, respectively).

inbreeding and iq - table 01

“Table 2 presents the results of the linear regression analyses. No significant regression was found between FROH and the cognitive measures after correction for multiple testing, although the association with non-verbal cognitive ability was nominally significant (P=0.03). Although this association was not statistically significant, it is noteworthy that every regression in Table 2 is *positive*, indicating that increased homozygosity tends to be associated with *higher* cognitive scores across different measures of cognitive ability (general, verbal and non-verbal).

inbreeding and iq - table 02

“Our analysis identified 87 loci where ROH overlapped in 10 or more individuals. For these overlapping regions we tested for association with each of the cognitive measures and again showed no significant associations after correction for multiple testing (P-values of less than 5.7 x 10-4). A sign test of the direction of effect across all ROH showed a disproportionately large number of *positive* associations, indicating that ROH are associated with higher cognitive ability (P=0.002). The sign test was non-significant for verbal ability but highly significant for non-verbal ability (P<10-6). The sign test for non-verbal ability alone remained significant after correcting for an individual’s genome-wide FROH score (P<10-6).

“As explained earlier, positive assortative mating can also lead to genome-wide homozygosity for trait-specific loci, and, unlike inbreeding, assortative mating can affect the high as well as the low end of the ability distribution. One possible explanation for the trend suggesting a positive correlation between homozygosity and cognitive scores in our data is that positive assortative mating on intelligence might be greater for high cognitive ability individuals….

“DISCUSSION

“Our results show that within a representative UK population sample there was a weak nominally significant association between burden of autosomal runs of homozygosity and higher non-verbal cognitive ability. This nominal association with *increased* cognitive ability is counterintuitive when compared with the results from more extreme inbreeding based on pedigree information. A potential explanation for this direction of effect is that individuals with higher cognitive ability might show greater positive assortative mating, which would lead to increased homozygosity at loci for higher cognitive ability in their offspring. However, in a separate sample we showed that greater positive assortative mating was not associated with higher cognitive ability. While these findings seem to provide clear evidence against this hypothesis, it is possible that the genome-wide genetic finding reflect historical mating habits that no longer exist today. It should also be noted that there was a reduction in the standard deviations for spousal correlations in the increased cognitive ability groups by an average of 6% compared with the decreased cognitive ability group (see Table 3), which could reflect less genetic variability in the high ability couples or a ceiling effect on the cognitive tests. This lesser phenotypic variability at the high ability end would have a small effect in reducing the spouse correlations and potentially confound our analysis….

“Overall, these results highlight the importance of understanding mating habits, such as inbreeding and assortative mating, when investigating the genetic architecture of complex traits such as cognitive ability. The results certainly suggest that there is no large effect of FROH on reduced cognitive ability, the expected direction of effect. The nominally significant associations found in this study may even suggest that in the case of non-verbal cognitive ability, beneficial associations with homozygosity at specific loci might outweigh the negative effects of genome-wide inbreeding and that the relationship between inbreeding and cognitive ability may be more complicated than previously thought.
_____

so, although obviously Further Research is RequiredTM, these researchers have concluded that both the absence of reduced cognitive ability and the slight increase in cognitive ability which they found in individuals who had runs of homozygosity (roh) in their genomes (evidence of matings between genetically similar individuals) were probably NOT due to assortative mating (i.e. smart people mating with smart people).

furthermore, they suggest that the inbreeding-causes-reduced-cognitive-ability meme is incorrect — or at least that the situation is more complicated than the idea that it’s the accumulation of recent deleterious mutations which haven’t been selected away that is the (whole) problem. in fact, a little inbreeding seems to have a positive effect on some cognitive abilities!

i’ve suggested a couple of times one way in which inbreeding might result in a low average iq in a population, and that is if the inbreeding leads to clannish, altruistic behaviors between extended family members which then result in the deleterious mutations NOT being weeded out.

one real world example i’ve offered is how life works in egyptian villages and how the more successful and affluent (and, presumably, more intelligent) members of a clan are obliged to help out their less successful and poorer (and, presumably, less intelligent) clan members. so, apart from mentally retarded individuals not reproducing, where is the negative selection for deleterious mutations here? there is none. or it’s a lot weaker than in more individualistic societies (like gregory clarks’ medieval england) where it’s more every man for himself — in clannish societies, deleterious mutations might be able to hang around for a long time, riding on the coattails of those with fewer deleterious mutations.

(note: comments do not require an email. i’m my own grandpa! [no, I’M not! it’s just the song.])

familism in the u.s. – whites by region

jayman says/asks:

“Theoretically, Red Staters are more able to depend on extended family. But here’s a question on the matter: is that true *today*? Are Whites in the South and West *today* more kin-centric? My (somewhat limited) experience in those parts of the country seems to indicate that they’re just about as individualistic as Blue Staters. I understand that kin-groups are still a major feature in Appalachia, but how about the rest of red America?”

**ALERT, ALERT!: READER REQUEST!** (^_^)

ok. so i looked at the “behavioral familism” related questions in the 2002 gss to see how whites in the different regions of the u.s. responded to the following questions:

– “How often do you contact your uncles/aunts?”
– “How often do you contact your nieces/nephews?”
– “How often do you contact your cousin(s)?”

the possible answers were:

– “More than twice in last 4 weeks.”
– “Once or twice in last 4 weeks.”
– “Not at all in last 4 weeks.”
– “I have no living relative of this type.”

as before, i collapsed the first two possible answers together to make a sorta “yes” repsonse (“yes, i’ve contacted that person in the last 4 weeks”).

here’s what i found (sorry, you might need your glasses to read these — wordpress has fixed it so that you can’t see a LARGER image in a new tab/window anymore. grrrrrr!):

gss 2002 - familism - u.s. whites - contact uncles & aunts

gss 2002 - familism - u.s. whites - contact newphews & nieces

gss 2002 - familism - u.s. whites - contact cousins

the patterns i see are:

east south central (alabama, kentucky, mississippi and tennessee), a consistently red state area, comes in twice with the highest ranking — and is above the national average on those two questions.
new england, a consistently blue state area, comes in once with the highest ranking — and, in fact, is above the national average on all three questions. so no one can accuse the new englanders of not being oriented towards the extended family!

the above average scorers on the three questions were (map of regions here):

new england – above average 3 times
east south central – 2 times
east north central (wi, il, mi, in, oh) – 2 times
west south central (tx, ok, ar, la) – 2 times
west north central (nd, sd, ne, ks, mn, ia, mo) – 2 times
south atlantic (de, md, dc, va, wv, nc, sc, ga, fl) – once

– the pacific states (ak, wa, or, ca, hi), a mostly blue region (with the exception of alaska), came in twice with the lowest ranking.
– the mountain states, a mostly red region, came in once with the lowest ranking.

the below average scorers on the three questions were (map of regions here):

pacific – 3 times
mountain – 3 times
middle atlantic (NEW YORK! nj & pa) – 3 times
west north central (nd, sd, ne, ks, mn, ia, mo) – one time
south atlantic (de, md, dc, va, wv, nc, sc, ga, fl) – one time
east north central (wi, il, mi, in, oh) – one time

to me, it seems like there’s an east-west divide — white familism decreases around the rocky mountains and gets even lower on the west coast. i should’ve made some maps. maybe i’ll work on that.
_____

so, back to jayman’s question: “Are Whites in the South and West *today* more kin-centric?”

yes, whites in the south are pretty kin-centric, but not so much in the west. and new englanders are very kin-centric — so there! (^_^) new yorkers are not.

i’ve got the data for african-americans, too, so i’ll check them out in another post.

previously: familism in the u.s. of a. and hispanic family values

(note: comments do not require an email. baby polar bear!)

civicness in the u.s. by race

following up on civicness in the u.s. by region, here is civicness in the u.s. by race.

the data are taken from the world values survey, 2005-2008 wave (2006 for the u.s.). note that these are people who claim that they are active members of voluntary organizations. here’s what i found (click on chart for LARGER view):

so totally, whites are a bit above average while blacks are a bit below average. hispanics, otoh, are quite a bit below average. the “others” (asians?) are in the lead, but note that the sample size for that group is rather small (n=62). (note that i also left out the “mixed race” category ’cause the sample size was way too small [n=14]. i also skipped the “other organization” category, again because the sample sizes were too small.)

african americans, then, are like their distant cousins back in africa — very civic-minded, civic here meaning inclined to join together in voluntary associations.

white americans score above average in joining: political parties, sports/recreation organizations, charities/humanitarian organizations, art/music/educational organizations, professional organizations and environmental organizations.

black americans score above average in joining: church/religious organizations (average), art/music/educational organizations and labor unions. the church/religious organization really seems to have pulled their total average up.

hispanic americans score above average in joining: church/religious organizations and labor unions, pretty much like they do back home.

previously: civic societies and civic societies ii and civicness in the u.s. (by region)

(note: comments do not require an email. voluntary association.)

democracy and the redistribution of wealth

more fun with the world values survey, 2005-2008!:

“Many things may be desirable, but not all of them are essential characteristics of democracy. Please tell me for each of the following things how essential you think it is as a characteristic of democracy. Use this scale where 1 means *not at all an essential characteristic of democracy* and 10 means it definitely is *an essential characteristic of democracy*: Governments tax the rich and subsidize the poor.

here are the percentages of people who answered 10 — government taxing the rich and subsidizing the poor is definitely an essential characteristic of democracy — for each nation:

for a change, i’m glad to see the anglos scoring so low. (^_^) i’m surprised that the scandinavians didn’t score higher; i guess they must simply understand that redistributing wealth, which is something they like to do, just isn’t an essential feature of democracy. the germans, always the over-achievers, score above average though.

in the u.s., more blacks (13.3%) than whites (5.8%) think that the redistribution of wealth is definitely an essential feature of democracy. hispanics are in between (7.0%) (click on table for LARGER view):

same in south africa. many more blacks (31.9%) and coloureds (24.7%) think that the redistribution of wealth is an essential feature of democracy than south african whites (6.9%):

and, what’s up with india?! 72.7% of the population think that the redistribution of wealth is an essential feature of democracy. wow. i did a breakdown by region, and northerners seem to hold this idea more than other regional populations of india, whereas easterners are not as fond of the idea:

what’s up with argentina, for that matter?

previously: dēmos kratos and democracy and civil rights and libyans on democracy: meh

*update 08/14: see also a sense of entitlement and a sense of entitlement ii

(note: comments do not require an email. the redistribution of wealth.)

interracial / interethnic marriage rates up in u.s.

from a new pew survey:

– About 15% of all new marriages in the United States in 2010 were between spouses of a different race or ethnicity from one another, more than double the share in 1980 (6.7%). Among all newlyweds in 2010, 9% of whites, 17% of blacks, 26% of Hispanics and 28% of Asians married out. Looking at all married couples in 2010, regardless of when they married, the share of intermarriages reached an all-time high of 8.4%.

– Gender patterns in intermarriage vary widely. About 24% of all black male newlyweds in 2010 married outside their race, compared with just 9% of black female newlyweds…. Intermarriage rates among white and Hispanic newlyweds do not vary by gender.

– [W]hite/Asian newlyweds of 2008 through 2010 have significantly higher median combined annual earnings ($70,952) than do any other pairing, including both white/white ($60,000) and Asian/Asian ($62,000). When it comes to educational characteristics, more than half of white newlyweds who marry Asians have a college degree, compared with roughly a third of white newlyweds who married whites. Among Hispanics and blacks, newlyweds who married whites tend to have higher educational attainment than do those who married within their own racial or ethnic group.

– Couples formed between an Asian husband and a white wife topped the median earning list among all newlyweds in 2008-2010 ($71,800)…. As for white female newlyweds, those who married a Hispanic or black husband had somewhat lower combined earnings than those who “married in,” while those who married an Asian husband had significantly higher combined earnings.

– Intermarriage in the United States tilts West. About one-in-five (22%) of all newlyweds in Western states married someone of a different race or ethnicity between 2008 and 2010, compared with 14% in the South, 13% in the Northeast and 11% in the Midwest.

– Several studies using government data have found that overall divorce rates are higher for couples who married out than for those who married in….

looks like a big report. lots to read. and data, too (state-by-state even)!

(note: comments do not require an email. snow day!)

european and european-american homicide rates not very different

olave’s got a post up — Correlation Data on Homicide and Race — in which he crunches some numbers and finds that the homicide rates in europe AND very white u.s. states are not all that different. homicide rates go up in u.s. states that have a greater percentage of blacks in their populations.

go see olave’s numbers here! me? i’m movin’ to new hampshire. (~_^)

(note: comments do not require an email. snow day!)

white males get more brain tumors

specifically, adult gliomas:

“Demographic Variation in Incidence of Adult Glioma by Subtype, United States, 1992-2007”

“For race/ethnic group variation, we observed an important commonality between GBM [glioblastoma] and non-GBM. For each subtype, compared to non-Hispanic Whites, the incidence rate among Blacks, Asian/Pacific Islanders, and American Indians/Alaskan Natives was substantially lower (one-fourth to one-half for GBM; about two-fifths for non-GBM). However, secondary to this primary effect, race/ethnic group variation in incidence was less for non-GBM than for GBM, a difference that was highly statistically significant but only moderate in magnitude.

“There is evidence for race/ethnic group differences in genetic pathways to glioma [31-33]. Furthermore, genome-wide association studies have identified several genetic susceptibility regions for glioma [34,35]. Given the genotype variability across race/ethnic groups [36], it is possible that variation in the frequency of susceptibility alleles across race/ethnic groups explains at least some of the race/ethnic group variation in glioma incidence, including the race/ethnic group heterogeneity in the relationship between glioma incidence and age. The commonality between GBM and non-GBM in race/ethnic group variation suggests that at least some of the susceptibility loci that may help explain race/ethnic group variation in glioma incidence would be the same for GBM and non-GBM, although some susceptibility loci appear to show specificity with respect to glioma subtype [37-39]….

“As with race/ethnic group variation, we observed an important commonality between GBM and non-GBM for sex. For each subtype, the incidence rate was higher for males than for females; this male excess of glioma is well known [2,3,5,6]. However, we did find the male/female RR to be somewhat higher for GBM (1.6) than for non-GBM (1.4), a result that was highly statistically significant. We previously suggested that the male/female difference in brain cancer incidence is biologically based [1], and that an explanation should be sought in genetic differences between males and females, sex hormones, and/or female reproductive factors [40]. Now we would add that any explanation should take into account the difference in the male/female RR between glioma subtypes….”

related?: Natural History of Ashkenazi Intelligence

(note: comments do not require an email. just ignore them and they’ll go away.)