Monday, November 12, 2007

Bottoms up ! -or - how water carries disease so its best to drink alcohol (Books - The Ghost Map by Steven Johnson)

One of the side benefits of reading Steven Johnson's history of the 1854 London cholera epidemic is the all the facts about other phenomena that one can learn along the way. That's not because Johnson's writing is desultory but rather because he knows that a scientific story is not just a parade of chronological facts about bacteria or the epidemiologist who tracked them down. The single microorganism that causes cholera doesn't exist in isolation, but interacts with hundreds of thousands of other organisms which, in turn, interact with hundreds of other factors including where we choose to settle or what we eat and drink. The disease spreads when the system that transports human waste away from our homes in running water (a commonplace fact most of us with internet access take for granted) somehow gets tangled with the other system that is bringing running water to our homes. Not an appetizing thought, but when thousands of people started living within close proximity of one another in cities, systems that transported water in two directions for these two uses became a necessity. Building them were huge urban construction projects in an age of burgeoning technological industry, they both made use of the sources of water already flowing - rivers - and, if you think about it, it all happened underground in the dark.

The prevailing theory at the time contented that disease spread through the "miasma" and was signaled by bad smells. A fascinating part of the book is Johnson's explanation for why intelligent people hung onto this notion for so long, even after the invention of the microscope?

It was as much a crisis of imagination as it was pure optics. To build a case for waterborne cholera, the mind had to travel across scales of human experience, from the impossibly small - the invisible kingdom of microbes - to the anatomy of the digestive tract, to the routine daily patterns of drinking wells or paying the water-company bills, all the way up to the grand cycles of life and death recorded in the Weekly Returns. If you looked at cholera on any one of those levels, it retreated back into the haze of mystery, where it could be readily rolled back to the miasma theory, given the pedigree and influence of miasma's supporters. Miasma was so much less complicated. You didn't need to build a consilient chain of argument to make the case for miasma. You just needed to point to the air and say : Do you smell that?

This is a story of interconnecting influences on multiple scales and Johnson is adept at switching between the microscopic and the macroscopic views. This is not just necessary for the truth of the story to emerge, it is also a technique that keeps us interested - it's one writers and filmmakers use all the time - shifting perspective.

My favorite bit of apparently tangential but actually integral piece of information was Johnson's brief history of drinking. He starts by telling us that the history of civilization is interconnected with the search for sources of clean drinking water:
For much of human history, the solution to this chronic public-health issue was not purifying the water supply. The solution was to drink alcohol. In a community lacking pure-water supplies, the closest thing to "pure" fluid was alcohol. Whatever health risks were posed by beer (and later wine) in the early days of agrarian settlements were more than offset by alcohol's antibacterial properties. Dying of cirrhosis of the liver in your forties was better than dying of dysentery in your twenties. Many genetically minded historians believe that the confluence of urban living and the discovery of alcohol created massive selection pressure on the genes of all humans who abandoned the hunter-gatherer lifestyle. Alcohol, after all, is a deadly poison and notoriously addictive. To digest large quantities of it , you need to be able to boost production of enzymes called alcohol dehydrogenases, a trait regulated by a set of genes on chromosome four in human DNA. Many early agrarians lacked that trait, and thus were genetically incapable of "holding their liquor." Consequently, many of them died childless at an early age, either from alcohol abuse or from waterborne diseases. Over the generations, the gene pool of the first farmers became increasingly dominated by individuals who could drink beer on a regular basis. Most of the worlds population today is made up of descendants of those early beer drinkers, and we have largely inherited their genetic tolerance for alcohol...The descendants of hunter-gatherers - like many Native Americans or Australian Aborigines - were never forced through this genetic bottleneck, and so today they show disproportionate rates of alcoholism. The chronic drinking problem in Native American populations has been blamed on everything from the weak "Indian constitution" to the humiliating abuses of the U.S. reservation system. But their alcohol intolerance most likely has another explanation: their ancestors didn't live in towns.

I had never heard this before, and found Johnson's ability to connect genetics, biology, and the history of settlement in cities in one long paragraph a real testament to his ability to synthesize multiple ideas into one inexorable narrative stream. So what does this all have to do with cholera?
Ironically, the antibacterial properties of beer - and all fermented spirits - originate in the labor of other microbes, thanks to the ancient metabolic strategy of fermentation. Fermenting organisms like the unicellular yeast fungus used in brewing beer, survive by converting sugars and carbohydrates into ATP, the energy currency of all life. But the process is not entirely clean. In breaking down the molecules, the yeast cells discharge two waste products - carbon dioixide and ethanol. One provides the fizz, the other the buzz. And so in battling the health crisis posed by faulty waste-recycling in human settlements, the proto-farmers unknowingly stumbled across the strategy of consuming the microscopic waste products generated by the fermenters. They drank the waste discharged by yeasts so that they could drink their own waste without dying in mass numbers. They weren't aware of it, of course, but in effect they had domesticated one microbial life-form in order to counter the threat posed by other microbes. The strategy persisted for millennia, as the world's civilization discovered beer, then wine, then spirits - until tea and coffee arrived to offer comparable protection against disease without employing the services of fermenting microbes.

Aside from my admiration for Johnson's lucid rendering of a complex set of facts, a more compelling case for drinking has never been made. 'Bottoms up' never had so many meanings.

1 comment:

Eva said...

That passage about alcohol and natural selection was quite interesting. Reminded me of Guns, Germs, and Steel. :)