Map of life expectancy at birth from Global Education Project.

Thursday, January 19, 2006

Re-reading Plagues and Peoples

Historian William McNeill published Plagues and Peoples in 1976. The book was important as a seminal effort at synthesis across disciplines. McNeill did his best to master ideas and knowledge in microbial ecology and disease vectors, the co-evolution of parasites and hosts, and infectious disease pathology, and then to plug this knowledge into our understanding of human history. He made a few mistakes, and at a few points he trumpeted speculation as confident conclusion, but he inspired a new way of thinking about humanity's place in the world, on the side of the humanities; and about infectious disease, on the side of epidemiologists and biologists.

Until the late 19th Century, nobody knew what caused infectious diseases and epidemics. Most of the measures that people took in response to them were useless or harmful. Cities were deathtraps whose populations could only be sustained by a continual influx from the countryside. Periodic episodes of mass dying occurred inexplicably amidst an ongoing random harvest of seemingly healthy people. Yet we now understand that these episodes were not random at all (nor were they divine retribution), but in fact they had a great deal to do with human patterns of habitation, migration, and agriculture. Conversely, they powerfully influenced these patterns, as well as the history of social domination and conquest.

We didn't begin to develop truly effective countermeasures until the mid-20th Century, and yet the brief time since World War II has been sufficient for those of us in the developed countries to completely forget what life was like before the present revolutionary era. With the conquest of smallpox, polio, tuberculosis, rheumatic fever, and most of the other great scourges of humanity, we came to believe that infectious disease would soon be essentially banished as a cause of death in the wealthy countries. The issue became one of global inequality, but even that seemed only a temporary situation.

The emergence of HIV changed our thinking, and powerfully vindicated the importance of McNeill's mode of cross-disciplinary analysis. It demonstrated, first of all, that microbial evolution could still outrun human ingenuity, with catastrophic consequences; while social science became the essential discipline for controlling the epidemic, in the absence of any biological technology for cure or immunization. (Yes, the very low-tech latex condom does the job, but it's a behavioral science problem to get people to use them.)

The threat of a flu pandemic also engages sociology and economics, of course, because we now understand that ordinary seasonal flu as well as flu pandemics are intimately linked to food production and distribution practices in which people live intimately with poultry and pigs, and bring live birds to large central marketplaces. Should a killer pandemic occur, we will gain a great deal more social science knowledge the hard way, by observing how people react -- knowledge which will be essential in preparing for the next infectious disease emergency. Then there are the issues of microbial drug resistance, biological warfare and terrorism, other emerging infections -- all of which centrally engage social science.

The evolving interdisciplinary approach to infectious disease gets a good, accessible discussion by Johannes Sommerfeld here in the journal of the European Molecular Biology Organization. So it's good news that people are putting their heads together about these problems. The bad news is, we haven't triumphed over infectious disease after all, and it is very likely that in the near future, a microscopic package of genetic information will once again change human history. At least this time, we'll know what it is.

(By the way, if you want to bone up on the biology of flu, and you don't mind concentrating really, really hard, head on over and see what Revere is doing at Effect Measure. I'll try to hold down my end here.)

1 comment:

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