Ancient urbanization and tuberculosis resistance.

Tuberculosis is a bit of a pet topic of mine, so this article from the March 2011 edition of Evolution caught my eye:

“Ancient urbanization predicts genetic resistance to tuberculosis.”

Barnes, I., Duda A., Pybus, O. & Thomas, M.

It is logical that an increase in urbanization and consequent close quarters association between large numbers of people would increase both the incidence and prevalence of various transmissible diseases. As described by Diamond in “Guns, Germs & Steel”, this leads to the tendency of a given urbanized population to develop greater rates of resistance to the pathogens responsible for these disease states. The article above explores this assumption by measuring the frequency of an allele (SLC11A1 1729 + 55del4) related to resistance to infection by Mycobacterium tuberculosis, the aetiological agent of tuberculosis, against the estimated length of time a given population has been urbanized. In reinforcing my initial statement, the results showed a strong positive correlation between how long ago a population shifted toward urban living and rates of this TB resistance related allele. So, as would be expected, more ancient population centres in the middle east for example showed relatively high frequencies of this allele when compared to southern African or Scandinavian populations.

The correlation between resistance related alleles and urbanization could be used for other, more novel, studies. For example, frequency testing for this allele or others associated with resistance to diseases endemic to urban centres, could be used in something of a ‘forensic’ manner to detect descendants of population centres that have undergone collapse i.e. the now dispersed members of ancient African or Mesoamerican populations.

On a side note; I found it a little unusual that this study also measured TB resistance against the time at which cattle were domesticated. As mentioned in a previous post (https://confusedious.wordpress.com/2011/04/19/tuberculosis-an-inverse-zoonosis/) it is highly unlikely that humans acquired this infection from cattle, the chromosomal data just doesn’t make sense in that context. Nor does the presence of TB in the New World make sense if cattle were the vector. With these things in mind I really hope they were simply speaking of M. bovis infection (as opposed to M. tuberculosis infection) only in terms of how it could produce a similar selection pressure for the given resistance allele. Even in this case I hypothesise that the role of M. bovis would relatively minor. Hopefully this particular myth of tuberculosis (of the human strain) as a zoonosis of bovine origins will someday find its rightful place in the dustbin.

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~ by confusedious on May 10, 2011.

5 Responses to “Ancient urbanization and tuberculosis resistance.”

  1. Interesting information. I spent time researching what diseases Homo erectus would have had a million years ago–was TB an issue then? or cancer? How about headaches? It’s hard to pin down, but I did come up with some studies that proved earliest man suffered from lice. It’s fascinating what we can deduce from artifacts, isn’t it?

    • Cancer would most certainly have been an issue, though what osteological evidence of it there is I am unsure. Virtually every other mammal can develop cancer so this suggests that the common ancestor of all mammals would have been susceptible. I’ll have to look that up. As for TB, to the best of my knowledge no genetic material pointing to M. tuberculosis has been recovered from any remains older than around 9000 years before present, so I can’t do anything but speculate about erectus in this context. M. tuberculosis shows a long history of coevolution with humans given its highly specific immune evasion strategies, so it has surely been with us for quite a long time (a good deal longer than the physical evidence can support at current). There is however evidence of rickets and a few other nutritional deficiencies in H. erectus.

      Lice are an interesting topic. Most species tend to have a given species of lice that infests their entire bodies, humans however, having two primary islands of hair; one on the head and the other a bit lower than the head, have one lice species dedicated to each hairy habitat. Some people even have the (dis)pleasure of hosting a third species of body lice. Interestingly, the head lice we host (genus Pediculus are pretty much the same as those found on chimpanzees, body louse are a cousin of head louse that most likely evolved after clothing use became widespread and lastly and perhaps most interestingly, pubic lice (Phthirus pubis) are more genetically similar to gorilla lice than anything else. What were our ancestors playing at?

      Oh by the way, my acceptance to the Australian National University for post-grad studies in biological anthropology has been processed, I’m just awaiting the paper work. I returned yesterday from Canberra with the good news. I’m pretty excited, ANU is the best university in my country and often in the top 20 for the world on the QS list, can’t believe my luck!

  2. Congratulations on your postgrad program acceptance! Welcome to the club 🙂

    While I largely agree that cancer is nothing new, I am convinced that the frequency of it was much lower– especially for the subtypes with a clear lifestyle/environmental component, such as most lung or colon cancers. I wonder if we have fossil evidence of things like osteosarcoma, which often affects young individuals and has strong genetic determinants…

    • Thank you very much! I was certainly very happy to be accepted! Where/what are you studying? Oh, scratch that question, I just re-read your about section. Epidemiology is a fascinating field, what was your thesis about?

      I would have to agree that certain lifestyle related cancers would have increased since the time of our ancient ancestors. Speculating here, but I think certain types of cancers would have increased much earlier than many would suspect, especially those related to alcohol. It has been made and consumed in fairly great quantities by humans for at least 9000 years, in fact, this may have led to lower rates of alcohol related cancers today as alleles for resistance have accumulated in populations (I have no citation for this, it’s a hunch, but I’d wager it’s true of at least some populations). Another thing to consider is that modern humans are relatively lacking in diversity at the genetic level when compared to many other species. An ancient bottleneck and the resulting gene pool reduction and drift could have also increased frequencies of some inherited cancers. This is actually a really interesting topic, thanks for bringing it to mind. I’ll have to see if there are any decent papers around exploring this idea.

  3. […] were brought to my attention by the good work of Confusedious: A Science Blog, and his entries on TB and its  possible […]

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