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Appendices to “Guns, Germs and Steel”

A particularly exciting part of scientific writing involves broad views on earth and human history; basically coming to very insightful conclusions starting from sparse and specific experiments. This is especially true when using archaeological data, which is very sparse and incomplete by its very nature. A prominent example of such broad insight on human history is “Guns, Germs and Steel” by prof. Jared Diamond, which represents a successfully attempt on removing racial prejudices regarding the reasons why western countries “succeeded” in conquering other civilizations. The most notable example is of course the south-american empires, but many other examples within African and Oceanian civilizations are presented. The bottom line of the book is relatively simple: the presence of domesticable plants and animals, together with a geographical configuration enabling exchanges boost technological advances. The relative western immunity to some infective agents derived from cattle domestication is also indicated as a decisive factor in the western expansion in America.

The book also features some pretty interesting bits, such as the accurate description of how a handful of Spanish soldiers kidnapped the Inca emperor Atahualpa (surrounded by 7000 soldiers!), and more interestingly how the Chinese empire (whose technological level has always been on par, if not more advanced than western civilizations) decided to abruptly stop naval explorations, therefore possibly changing the world’s history with such single minor decision.

Many critics to this book focus on the lack of clear and specific experiments that could confirm some of the most challenging conclusions of the author: Tom Tomlinson summarizes such critics by saying “it is inevitable that Professor Diamond uses very broad brush-strokes to fill in his argument”. It doesn’t necessarily need to be that way though: in another book by Walter Alvarez, every single experiment that led to the conclusion that the cretaceous mass-extinction was caused by a giant rock falling from the sky is clearly outlined and explained, including other quite convincing alternate theories. (As a side note, the book has the best name ever invented: T-rex and the crater of doom).

Given the use of this “broad brush-strokes”, it is inevitable that new experiments will eventually pop-out and provide details that could change the interpretation given by professor Diamond, maybe not completely, but at least by posing significant challenges, or the need to update parts of the book.

By chance I stumbled upon some very interesting studies that would very well fit as appendices to the book. The first study involves tuberculosis, which is one of the illnesses that badly affected south-american populations after contact with the conquistadores. The first deviation from Diamond’s theory is the fact that Mycobacterium tuberculosis (the bacteria causing the disease) was probably transmitted from humans to domesticated animals and not the contrary; the other more challenging discovery is the presence in Peru of human bones showing clear signs of tuberculosis some 300 years before Colombo set foot in the Americas. Luckily enough the bacterial DNA in those bones was still readable and allowed the authors of this study to conclude that tuberculosis was brought in Peru by… sea lions. This study itself is also another example of a huge insight coming from sparse and incomplete data: much of the conclusion relies on 5 non-synonymous SNPs shared between the Peruvian strain and those that infects modern-day sea lions; there are of course a number of other experiments in the article, making the conclusion pretty robust. It is entirely possible that the distance with the “regular” western tuberculosis was such that native populations had less resistance, but it also shows how new emerging experiments can threaten parts of a convincing theory. The devil is indeed in the details.

The other three studies all came in this week, as I attended a very interesting talk by Eske Willerslev on the analysis of ancient genomes (the oldest so far being a 700’000 years old horse!). The first study somewhat challenges Diamond’s idea that most of the large mammals have gone extinct by human intervention (thus reducing the availability of domesticating cattle for some civilizations), but could instead have been caused by a drastic reduction in the presence of some protein-rich plants after the end of the latest ice age. The other quite amazing couple of studies suggest that there have been contacts (and you know, admixture) between south-americans and Polynesians: this conclusion is based on two specular experiments: genotyping of natives from Rapanui and of two individuals belonging to the Brazilian Botocudos population (which actually seem to show no signs of native american origin). According to the genetic data this encounter has happened no later than about 1400. This exciting conclusion promises to revise the way human migrations in the new continent are currently taught, and it is also very likely that new surprises will pop out sooner or later.

P.s. I’m pretty sure that there will be many other studies out there challenging Diamond’s book details that I completely ignore :)

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