Sunday, May 17, 2009

High blood pressure and germs?   posted by Razib @ 5/17/2009 01:38:00 AM

High Blood Pressure Could Be Caused By A Common Virus, Study Suggests:
A new study suggests for the first time that cytomegalovirus (CMV), a common viral infection affecting between 60 and 99 percent of adults worldwide, is a cause of high blood pressure, a leading risk factor for heart disease, stroke and kidney disease.

Interesting in light of Jean-Laurent Casanova's research program on genetic susceptibilities to infectious disease. The original paper is here. If many more diseases turn out to be contingent upon infection can the hypochondriacs please get a little more sympathy?


Wednesday, October 29, 2008

Disease driven human evolution?   posted by Razib @ 10/29/2008 09:04:00 PM

Gene Expression Profiles during In Vivo Human Rhinovirus Infection (also, ScienceDaily summary):
Rhinovirus infection significantly alters the expression of many genes associated with the immune response, including chemokines and antivirals. The data obtained provide insights into the host response to rhinovirus infection and identify potential novel targets for further evaluation.

About those viruses:
Epidemiologists have established minimal population size and density thresholds for particular diseases (such as measels, mumps, rubella, smallpox, influenza, rhinovirus) to survive and spread. In small hunter-gatherer groups or even small farming villages, such diseases would have been incapable of spreading very far and woul have disappeared (Black 1975). This implies that many diseases must be recent.

There's a reason that some of the cites for the adaptive acceleration theory use microbial models; here are lot's of them and they breed fast. Microbiologists are fond of reminding people that on the order of 90% of the cells in your body are bacteria resident in your gut; but I wonder if the last 10,000 years might not have been a boon for a whole host of virulent less friendly microbes which "tag along" with H. sapiens.

Related: Toxoplasma gondii & human culture, Obesity germs, thrifty genes, Another Nobel for the New Germ Theory of disease and Toxoplasma gondii's South American origins and its influence on culture.

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Wednesday, October 15, 2008

Geordies are dirty?   posted by Razib @ 10/15/2008 05:51:00 PM

English Northerners' Hands Up To 3 Times Dirtier Than Those Living In England's South:
The results indicated that commuters in Newcastle were up to three times more likely than those in London to have faecal bacteria on their hands (44% compared to 13%) while those in Birmingham and Cardiff were roughly equal in the hand hygiene stakes (23% and 24% respectively). Commuters in Liverpool also registered a high score for faecal bacteria, with a contamination rate of 34%.

In Newcastle and Liverpool, men were more likely than women to show contamination (53% of men compared to 30% of women in Newcastle, and 36% of men compared to 31% of women in Liverpool), although in the other three centres, the women's hands were dirtier. Almost twice as many women than men in Cardiff were found to have contamination (29% compared to 15 %) while in Euston, they were more than three times likelier than the men to have faecal bacteria on their hands (the men here registered an impressive 6%, compared to a rate of 21% in the women). In Birmingham, the rate for women was slightly higher than the men (26% compared to 21%).

GNXP readers will know that these sorts of data might imply more than just public health issues.


Tuesday, October 07, 2008

Another Nobel for the New Germ Theory of disease   posted by agnostic @ 10/07/2008 09:41:00 PM

In 2005, Barry Marshall and J. Robin Warren won the Nobel Prize in Physiology or Medicine for showing that a pathogen was behind the common diseases gastritis and peptic ulcers. Now the 2008 Prize goes to Harald zur Hausen, who showed that pathogens cause the common disease cervical cancer. As far as theory is concerned, these findings are not surprising (PDF). The most recent New Germ Theory winner before these two was Peyton Rous in 1966, whose work on cancer-causing pathogens began in 1911. You might also count Johannes Fibiger's 1926 Prize for what was thought to be a cancer-causing nematode.

And two of the early winners -- Koch in 1905 and Laveran in 1907 -- contributed to the Original Germ Theory of disease. So after 100 years, perhaps people are finally starting to take the idea seriously? Common disease-common variant researchers in human genetics may get more media coverage, including the science media, but the Germ Theory people are cleaning up where it counts.


Wednesday, February 27, 2008

More pathogens means more collectivism?   posted by Razib @ 2/27/2008 07:07:00 PM

Pathogen prevalence predicts human cross-cultural variability in individualism/collectivism (Open Access):
...We suggest that specific behavioural manifestations of collectivism (e.g. ethnocentrism, conformity) can inhibit the transmission of pathogens; and so we hypothesize that collectivism (compared with individualism) will more often characterize cultures in regions that have historically had higher prevalence of pathogens. Drawing on epidemiological data and the findings of worldwide cross-national surveys of individualism/collectivism, our results support this hypothesis: the regional prevalence of pathogens has a strong positive correlation with cultural indicators of collectivism and a strong negative correlation with individualism. The correlations remain significant even when controlling for potential confounding variables. These results help to explain the origin of a paradigmatic cross-cultural difference, and reveal previously undocumented consequences of pathogenic diseases on the variable nature of human societies.

The, r = -0.69 at p-value 0.001 and n = 68. You can find the raw data here. It would be cool to see trends within nations/societies. For example, variation in altitude.

Related: Toxoplasma gondii & human culture.

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Thursday, February 21, 2008

Where be the bugs?   posted by Razib @ 2/21/2008 03:28:00 AM

Cool paper in Nature, Global trends in emerging infectious diseases. Not cool because infectious diseases are great, but I believe they've been (and are) major evolutionary pressures on our species. Great map too. From the legend:

a) zoonotic pathogens from wildlife
b) zoonotic pathogens from non-wildlife
c) drug-resistant pathogens
d) vector-borne pathogens

Not surprised about the intersection with world population density. Just by inspection, the Indo-Gangetic plain looks to be the "winner" here! Though it does seem that Sub-Saharan Africa holds its own in terms of representing above its population-weight class in the wild-life derived and vector-born pathogen categories. Might we be able to chalk that up to a long history of coevolution between the African ecosystem and hominid species? Domesticated animals seem to be more of an issue in the old Eurasian Oikumene as you would expect. For more precision on the global trends and correlates, check out their regressions.


Sunday, August 05, 2007

Climate and civilization follow-up   posted by agnostic @ 8/05/2007 07:12:00 PM

Recently I suggested that civilization flourishes in some areas of the world more than others, in part, because winged insects thrive more in environments that are lower in elevation and latitude. These insects are a key source of chronic infectious disease in humans, and having to deal with the recurring symptoms must sap some of your body's resources that could be used for "luxury" processes involved in societal innovation. I neglected to mention that what likely makes wingedness more common in such environments -- a higher degree of environmental heterogeneity -- likely selects for an increase in migratory features more broadly, not just in insects. So some small animal may be more migratory, and it could be carrying parasites or pathogens itself, or be harboring insects that carry pathogens. It's just a lot easier for disease vectors to make their way to you in such environments. And of course, it may be that the fatigue caused by hot, humid weather makes you less productive.

Since then, I looked again at Inductivist's analyses on White IQ in various regions of the US, based on GSS data. In the first two posts (here and here), he showed that adults in the Mountain (MTN) region score better than average on mean IQ and percentage of holders of college degrees. More interesting, though, is the post on IQ and geographical mobility. Although New England and the Mid-Atlantic far and away attract the smartest Whites, the smartest of all are the NE transplants who were raised in MTN. Moreover, none of the bottom 10 pairs consisted of a group that was raised in MTN. By contrast, even though 2nd place goes to those raised in East South Central and who moved to NE, those raised in ESC also occupy 4 of the bottom 10 spots.

Why does growing up in MTN appear to boost your IQ? Probably because the climate is less favorable to the spread of pathogens by vectors that are migratory. And that, again, is probably due to less environmental heterogeneity in that area -- the Rockies are cold, dry, and very high in elevation, all tied to greater environmental stability. That's surely one reason why Colorado in particular performs so well, and its state government should publicize the hell out of Inductivist's findings to draw in wealthy parents who want the best environment for their kids. "Baby Einstein" pre-schools won't accomplish squat, but being raised in the salubrious climate of the Rockies sure will. Even the hot areas in the southern part of MTN, which are less impressive than the northern areas, are not humid or sub-tropical but desert, which is characterized by little environmental change over time or across space.

You might think that the lower population density is also a factor, and that could be, but people raised in regions with high density make a good showing in Inductivist's ranking. Population density is more critical in influencing acute, contagious diseases like the flu or perhaps rarer and wilder stuff like schizophrenia. But it could be that adult IQ is more influenced by the presence of chronic infections that continually disturb the development process. As before, knowledge of which pathogens and which vectors are the culprit is not necessary to believe this idea: just knowing that the local ecology in region X favors such things far more so than in region Y is enough to suspect that diminished IQ in region X is at least partly due to infection.

Moving on to larger concerns, one puzzle that I admitted in the original post was South Asian civilization -- isn't that one of the nastiest places to be climate-wise? I should've investigated further, because the answer is "yes and no." The climates in the Subcontinent vary a lot more than I thought, as you can see in this climate map of India and this climate map of the world. But does climate correlate with degree of civilization in South Asia? Beats me, since I couldn't say which areas over the long-haul show more development than which others. However, I have catalogued below a list of the climates for the capitals of South Asian civilizations beginning in the Neolithic. I used the chronology of Wikipedia's History of India article for convenience, and looked up the capitals there as well.

I'll leave it up to the more historically informed to say whether the hypothesis is supported or not My rough impression is that the North has shown greater development over the past several thousand years, even though the civilizations of the South and Bengal have been no slouches, but that may be wrong in general or perhaps correct broadly but wrong in finer detail. One interesting exception to the rule of Southern climates being more tropical, though, is that of Bangalore -- the "Silicon Valley of India" -- which enjoys a semi-arid climate, lies higher above sea level than Madrid (920 m vs. 667 m), and is known as a "Garden City."

And yes, I know that the current climates where the earliest civilizations flourished might not be identical to what they were at the time, but Iran and the modern countries occupying the Fertile Crescent also have mostly arid or semi-arid climates nowadays. The point is that they didn't consist of tropical wet & dry climates like you find in Sub-Saharan Africa or the Amazonian rainforests.

Civilization (:capital) -- climate

Mehrgarh -- arid

Indus Valley -- arid, semi-arid

Mahajanapadas -- arid, semi-arid, humid sub-trop

Magadha: Rajgir -- humid sub-trop

Maurya: Patna -- humid sub-trop

Satavahana: Pune, Paithan, Amaravati -- humid sub-trop

Kushan: Charikar -- highland, semi-arid; Taxila -- semi-arid; Mathura -- semi-arid

Gupta: Ujjain -- semi-arid; Patna -- humid sub-trop

Pala: Varendra / Rajshahi area -- humid sub-trop; also trop wet & dry

Chola: Tiruchirappalli -- semi-arid, trop wet & dry; Poomphuhar -- trop wet & dry; Gangaikonda Cholapuram -- trop wet & dry

Delhi Sultanate -- semi-arid

Deccan Sultanates -- semi-arid, trop wet & dry

Hoysala: Belur, Halebidu -- trop wet & dry

Kakatiya: Warangal -- trop wet & dry

Vijayanagara -- semi-arid

Mughal: Agra, Delhi -- semi-arid

Sikh Confederacy -- semi-arid, humid sub-trop

Maratha: Pune -- trop wet & dry

Post-Independence: New Delhi -- semi-arid; Islamabad -- semi-arid; Dhaka -- humid sub-trop, trop wet & dry

NB: I left out the period of colonial India for a few reasons that you might object to. First, Europeans certainly cope differently with non-European climates than do the locals, and I want to see whether climate affects degree of civilization even for those who are most adapted to life there. And second, it's my understanding that Europeans were more concerned with establishing superior trading posts and practicing mercantilism than they were with encourgaging civilization per se in South Asia.

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Tuesday, June 19, 2007

Winged insects and degree of civilization   posted by agnostic @ 6/19/2007 10:30:00 PM

A recent article in Nature, which we blogged about here, reviewed the consequences of agriculture on the nature and prevalence of pathogens that have plagued human beings. One key datum that Wolfe et al. (2007) discuss is the difference between the vectors (or transmitters) of infectious disease in the tropical vs. non-tropical regions, where agriculture has flourished the longest: almost all of the nasty infectious diseases in the tropics are spread by winged insects [1], whereas most of those in the more advanced areas are spread by human-to-human contact, polluted water, or parasites of small animals (such as the fleas that spread the Bubonic Plague). One consequence of this is that, as the authors note, infectious diseases in the tropics tend to be chronic rather than acute -- in crowded populations that characterize agricultural societies, it won't take long for you to pass your germs to someone nearby, after which point you've served your purpose and can be left alone for the time being (if you aren't shortly killed). If there aren't many people nearby to infect, you're going to have to serve as the host for much longer.

The authors do not note, however, an important evolutionary reason for why the geography of tropical regions causes them to be more plagued by insect-transmitted disease. This shortcoming is odd considering that one of the authors, Jared Diamond, has written best-selling books on human evolution (The Third Chimpanzee) and geography and civilization (Guns, Germs, and Steel). I haven't read either of these in full, so to be sure he didn't cover this issue in GGS, I searched it at Amazon and found no discussion of the prevalence of wingedness among insects. In any case, the key pattern is that the proportion of insects that are winged increases as both latitude and altitude decrease. At a more fine-grained level, wingedness is more common in habitats that are in some sense temporary or unstable, while flightlessness is more common in more permanent, stable habitats [2].

The basic insight comes from life history theory: in unstable habitats, an individual may be born into awful conditions due to temporal and/or spatial hetereogeneity. Here, it will pay to have a means of migrating to a more hospitable area, while in less volatile habitats an individual probably won't get caught with their pants down, and so flightlessness would increase. Just think of the energy a bug would save by not growing and maintaining their wings if it didn't need them. Most tropical areas have all three features: low in elevation, close to the equator, and more unstable habitat-wise [3]. It's no surprise, then, that such areas are more wracked by insect-borne infectious diseases. There are simply far more winged bugs that can travel far distances transmitting pathogens to humans.

One consequence of all this chronic disease must surely be increased difficulty in founding, let alone maintaining, a great human civilization. Chronic diseases which begin to strike early on in life are likely one reason that mean sub-Saharan African IQ is about 70, while mean African-American IQ is about 85, a full standard-deviation above. Possible mechanisms are not difficult to think of: the parasite that causes Sleeping Sickness get into your brain and slowly destroys it, your body may divert resources to disease defense and repair rather than on "luxury" items like higher IQ, and so on.

Even controlling for IQ, being afflicted with chronic disease must sap one's ability to doggedly pursue long-term projects, whether artistic or scientific, that foster civilization. Probably the best shot sub-Saharan Africa has is south of the Zambezi River, which doesn't suffer from a tropical hellhole climate. At best they could reach the level of African-Americans, who don't dominate Silicon Valley, but who have contributed scores more to the world's culture than Africans in sub-Saharan Africa. [4] Even in the US, most high African-American culture has largely sprung from cities outside of the dreadful "humid subtropical" climate of the Southeastern states (for example, New York and Chicago).

That pattern is also evident among American Whites, by the way: at the most northern fringe of the Southeastern US there are first-rate research universities (Duke and UNC - Chapel Hill, both in North Carolina), but the region is largely bereft of civilization-propelling institutions. In fact, blogger Inductivist has shown, using General Social Survey data on Whites, that it is a larger source of and magnet for duller Whites, compared to other regions (see here and here). Now, clearly I'm not proposing that epidemic Sleeping Sickness, malaria, etc. are causing the problem in the US. But whatever the more numerous bugs in the Southeast are transmitting to humans, it could partially account for the discrepancy between its level of culture and that of the Northeast. Indeed, from Inductivist's reckoning, it appears that most intelligent people with any sense from that region decide to haul ass to the Mid-Atlantic and New England states.

[1] From p. 280 of Wolfe et al:

A higher proportion of the diseases is transmitted by insect vectors in the tropics (8/10) than in the temperate zones (2/15) (P less than 0.005, chi-square test, degrees of freedom, d.f. = 51). This difference may be partly related to the seasonal cessations or declines of temperate insect activity.

[2] For a brief overview, see pp. 349-56 of Roff (2002). For extensive literature reviews, simulations, and so on, see Roff (1990) and Roff (1994).

[3] As for the non-obvious claim of greater temporal variation as you move toward tropical areas, see Roff (1990: 405):

I tested the hypothesis that habitat persistence varies with latitude with data on the rates of succession on abandoned farmland. In the northerly states of the United States (Wisconsin, New Jersey, Illinois, and New York) shrubs appear only 10-20 yr after abandonment, and even after 40 yr succession does not proceed beyond a very open woodland/parkland condition (Thomson 1943, Bard 1952, Bazzaz 1968,1975, Mellinger and McNaughton 1975, Pickett 1982), while in the more southerly states of North Carolina, Tennessee, and Georgia a closed canopy is formed within 15-30 yr (Billings 1938, Oosting 1942, Quarterman 1957, Nicholson and Monk 1974, 1975, Lindsay and Bratton 1980). In the Mexican tropics invasion by trees occurs within the first 2 yr, and these may reach a height of 10 m within 5 yr (Purata 1986): in the upper Rio Negro region of the Amazon Basin a loose canopy of Cecropia spp. 5 m high was formed within 22 mo (Uhl et al. 1981).

Sidebar: Detroit is fortunate to be situated as far north as it is, or else the reclamation of the city by the wild would have wholly swallowed up most of the area long ago (see here too).

[4] Alternatively, they could follow the lead of the elite strata of South Asia, who have managed to build a civilization despite vying with tropical Africa for status as the world's chamberpot of infectious disease. There, though, the elites have striven for centuries to isolate themselves genetically from those in lower castes, as well as to minimize their physical contact with the even more bug-bitten lower classes.


Roff, D. (1990). The evolution of flightlessness in insects. Ecological Monographs, 60(4), 389-421.

-------- (1994). Habitat persistence and the evolution of wing dimorphism in insects. The American Naturalist, 144(5), 772-98.

-------- (2002). Life History Evolution. Sinauer Associates: Sunderland, MA.

Wolfe, N., C. Dunavan, & J. Diamond (2007). Origins of major human infectious diseases. Nature, 447, 279-83.

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Tuesday, May 01, 2007

Toxoplasma gondii's South American origins and its influence on culture   posted by agnostic @ 5/01/2007 11:03:00 PM

Would there have been a Goya without the Columbian Exchange?

It would require many volumes to catalogue the ways in which human gene flow from Iberia and Africa into South and Central America has affected the history of the New World, while at first blush the matter of human gene flow from the Americas into Iberia and Africa might merit little more than a book or two. However, humans are not the only living things whose genes might flow in one direction or another. A simple example is corn, which when introduced into Spain became a popular staple among peasants -- so much so that many were plagued by an epidemic of pellagra for relying solely on corn, which lacks niacin. But is it possible that gene flow of another sort might have affected European high culture? After all, when we think of the culture of Spain, we typically think of The Golden Age writers, Goya, Gaudi, Segovia -- not outbreaks of pellagra.

A short and freely available article
from last year in PNAS argues pretty persuasively that the pathogen Toxoplasma gondii, which has already been shown to affect human personality and culture, originated in pre-Columbian South America. The reasoning is simple: it is much more polymorphic at neutral sites within South America, and shows a striking lack of diversity elsewhere. The less diverse forms elsewhere likely reflect smaller founder populations that were carried away on European ships. (The same reasoning suggests that Africa is the ancestral homeland of human beings.) As the Europeans returned from their initial voyages to South America, they probably brought back with them infected cats and rats, as well as soil contaminated by cat feces. Because Iberia was an agricultural society with greater population density than pre-Columbian South America, T. gondii likely found much more ideal conditions for increasing its virulence, not to mention that European populations were innocent of its existence and so likely had no defenses. The authors argue that, from there, maritime travel spread the pathogen to the rest of the world.

As Razib mentioned in his review of the study that showed T. gondii's effect on human personality, the germ has somewhat different effects on men vs women. Since we're considering high culture, we need only concern ourselves with its effect on males. The short and skinny is that it raises levels of novelty-seeking and Neuroticism, a trait that measures how easy it is for a person to become emotionally worked up. One study by Cattell found that eminent researchers he interviewed tended to be more emotionally stable. For artists, though, you don't really need me to tell you that they tend to be emotionally excitable. Novelty-seeking is obviously important for both domains.

To return to the theme of genius germs, artists show a stronger bias toward being born during the Winter and Spring than scientists, which is consistent with the hypothesis that an early infection (more likely during the "flu season") starts the individual's personality off on a more Neurotic groove. So perhaps the flourishing of T. gondii among a virgin European population contributed to the explosion of artistic creativity that we see starting about the 17th Century. Greg Clark's new book, A Farewell to Alms, argues that the Industrial Revolution could not have happened far earlier than it did, in part because the English were simply not genetically prepared for it -- they were predisposed to abandon rather than conscientiousness. Maybe the same is true for artistic revolutions -- a population may have to wait for an outbreak of nuttiness in order to produce a Beethoven or a Goya. As the population adapts defenses against pathogens that affect personality, and as sanitary conditions improve, the frequency of bona fide weirdos diminishes, and what remains are faux iconoclasts like we see in Modern Art. Andy Warhol is a good example: his eccentricity was probably little more than an affectation.

The case of Western Classical music is particularly instructive, and anyone's theory of what produces artistic genius has to contend with this medium and time-frame. Unlike all other art forms, there is almost nothing of impressive value from "Ancient music" or even most Medieval music. There is a hint of sophisticated music during the Renaissance, and then suddenly there is an explosion during the Baroque, Classical, and Romantic eras -- after which there is a figure here or there who you might compare to a "mediocre" Baroque composer, but none you would comfortably rank alongside Bach. The early great works of the Baroque begin about the 1720s, and by the mid-1800s most of the rest of the Greats were dead; Wagner died toward the end of the 19th C., and most of the leading candidates for "Great 20th Century compositions" debuted before 1920. How can the near entirety of an artistic domain have been created within scarcely 200 years, burning out as abruptly as it caught fire?

I initially thought an epidemic of some infectious disease was likely, since there were plenty of outbreaks of cholera, typhoid, and others back then. Syphillis, maybe? That seems plausible at first, but that disease really does appear to make you quite nuts. If it were something less severe, but that still affected the brain and personality, it could have been the newly introduced T. gondii germ, which would have taken some time to reach Germany and France. England actually has quite low levels, despite Britons' reputation as cat-lovers, and they have never produced a composer on the level of any Continental -- and not because there was no demand for or encouragement of such music. When Haydn arrived in London, he was overwhelmed by how greatly he and other Continental composers were worshipped in England. The only composer of high eminence who can claim to be an Englishman was in fact a German import: Handel. The Scandinavian countries likewise were not principal actors during the great period of classical music; the population there is more spread out, and the climate is much colder, so T. gondii might have had a harder time causing epidemics there (current levels are also very low there). Iberia and Italy would have been struck early since they have more hospitable climates and have many ports that would have welcomed ships returning from the New World.

Surely there are many necessary conditions for artistic genius to flourish, and to reiterate the point of another post on extreme deviations, if one component is lacking, the entire edifice collapses. Before and after the great period of Western music, all of the other components may well have been in place, waiting for an outbreak of oddballness. These days, no one would allow a purposeful epidemic in the hopes that it might produce one Beethoven among the millions of other lives it would ruin, so we may have to just wait for something similar to happen naturally and hope that some good comes of it. Until then, if my conjecture is on the right track, those who treasure Western high culture may owe a debt of gratitude to an obscure South American parasite that we contract via infected cat shit.

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