Question

As is well known, when the Spanish first arrived in the New World, they brought with them a number of diseases that had a serious impact on the indigenous populations.

Why is it that there was microbiological asymmetry between these two populations of humans? In other words, why were there not a number of diseases unfamiliar to European immune systems that had a similarly devastating effect?

Answer 1

Most theories have to do with how different agricultural practices affected the transmission patterns and prevelence of diseases in the Americas and the old world.

Epidemic diseases were first transmitted to humans from the animals they domesticated or otherwise came into close contact with (I wouldn't say humans ever domesticated rats) - but these diseases only established stable transmission patterns in their hosts in animal populations which had lived in close enough proximity to each other long for a very long time. The old world had those vectors in the form of cattle, horses, rodents, etc., while the potential disease reservoirs in the America - llamas, alpacas, etc - did not live in sufficient population densities to maintain epidemic diseases which were transmitted from animal to animal.

There were significant differences in agricultural crops and practices between the two. The American crops like maize and potatoes have higher calorie per land unit ratios than the old world crops, which limited the extent to which the concentrated Amerindian civilisations depended on animal husbandry for food - and so limited their exposure to potential domestic animal vectors. Also, it enabled them to establish much higher population densities in urban areas which enabled faster transmission of epidemics once established.

Also, agriculture in the old world depended from its inception on irrigation. Most of the rural population spent a great deal of time working in standing water which favoured the spread of disease organisms (in some cases, it eliminated the need for an animal intermediate) and provided a competitive advantage for individuals with immune systems which were robust both to general and specific challenges. Agriculture in the new world did not.

There is also the matter of which culture visited which other culture: it was a few Europeans who spent a six months on the boat, inoculated the relatively large number of Amerindians they contacted and then spent six months on the boat going back essentially in quarantine.

There is also a genetic argument, although it is tied up in all the speculation about how precisely people initially colonised the Americas. Theory has it that the Amerindians were descended from a small, genetically isolated subsample of the old world population which evolved away from the major prehistoric centres of disease confluence - which were in the regions of intense agriculture and animal husbandry Middle East, Africa, India and southeast Asia while the new comers probably came from Northern Asia - and so had not been subject to the selective pressures which favoured the prevalence of disease resistant genes in their old world descendants.

And lastly there is some feeling that the Amerindians actually did give at least two diseases - syphilis and typhus - to the Europeans. These diseases were not documented in pre-contact Europe (although the disease organisms might have been present in other forms of illness and their appearance merely reflects a change in transmission patterns); however, they spread quickly enough after it, especially in port cities like London and Lisbon before establishing stable transmission patterns over the course of a couple centuries.

A more detailed discussion can be found in the seminal (and somewhat speculative) work in this field, "Plagues and Peoples" by William H. McNeill and in the literature which followed it.

Answer 2

There were, the real issue was the nutrition of the two populations... and as i started typing blues posted that huge thing--and he probably mentioned everything I was going to... lol

Answer 3

Sorry, but a wonderful question and merited a thorough answer. I hope people don't find it onerous.

Answer 4

I found it useful. The one thing not mentioned was the European's use of citrus (to prevent scurvy), which enhances immune response time and nutrient uptake (eg Vitamin C). And their use of Beer and Wine and not water as their main drink--in fact the pilgrims were dropped where they were when the sailors realised they were going to run out of beer for the return trip. It is much harder to get waterborne diseases through fermented drinks like beer and wine, thus the vector for a large number of the new protozoan diseases was eliminated.

Answer 5

I was listening to a program on Spanish radio yesterday about the Incan Empire and they mentioned the effect of disease of los conquistadores, a story I've heard many times before. But finally got around to asking myself why it was so asymmetric only now.

Thanks Blues for the detailed response.