I’ve just read The Ghost Map by Steven Johnson. This extraordinary book, which nominally chronicles the campaign of physician Dr John Snow to persuade Victorian England that cholera was caused by contaminated water rather than noxious odours, also takes the reader on long and fascinating asides into topics like how living at density selected for alcohol-tolerant genes.
As this article points out, large cities in all parts of the world used to be very dangerous places where the very proximity of humans directly led to disease and death.
I already knew the basics of John Snow’s battle with the established order and his famous map of Broad Street from TV programs and the odd book, like Mathew Kneale’s excellent novel about a Victorian hydraulic engineer, Sweet Thames.
But the particular value of Stevenson’s take on London’s cholera epidemic is the attention it gives to the broader circumstances of the times and the way he burrows deeply into the underlying social, medical and technological issues.
He talks, for example, about how humans living at close quarters historically addressed their vulnerability to polluted water by drinking alcohol instead (notwithstanding it is itself poisonous and addictive). Nothing new about that perhaps, but what is interesting is how the desire to live at higher density gradually selected for genes that could tolerate alcohol:
To digest large quantities of alcohol, 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 generations, the gene pool of the first farmers became increasingly dominated by individuals who could drink beer on a regular basis. Most of the world’s population today is made up descendents of those early beer drinkers, and we have largely inherited their genetic tolerance for alcohol (the same is true of lactose tolerance, which went from a rare genetic trait to the mainstream amongst the descendants of the herders, thanks to the domestication of livestock)”.
Alcohol was not of course a complete solution to humans living close together. The germs that flourished with the increasing tendency of their hosts to live cheek by jowl were ultimately only kept in control by technology – in the first instance by mass engineering projects, like the sewerage schemes that eventually followed from Snow’s ground-breaking work.
Another of the many insights the book provides is how Victorian London went about dealing with waste disposal prior to the construction of efficient waste infrastructure. A vast army of workers subsisted by recycling the waste and detritus of London – it included bone-pickers, rag-gatherers, pure-finders, dredgermen, mud-larks, sewer-hunters, dustmen, night-soil men, bunters, toshers and shoremen (pure-finders collected dog shit used to take the hair off hides).
“We’re naturally inclined”, Stevenson says, “to fulminate against a system that allowed so many thousands to eke out a living by foraging through human waste”. But he cautions that such social outrage:
should be accompanied by a measure of wonder and respect: without any planner coordinating their actions, without any education at all, this itinerant underclass managed to conjure up an entire system for processing and sorting the waste generated by two million people…and the scavengers of Victorian London weren’t just getting rid of that refuse – they were recycling it”.
Something like this still happens today in squatter settlements where waste removal infrastructure is basic and minimum wages and welfare are low.
Stevenson also spends some time looking at the tendency of people to cling to “wrong” ideas. He wonders why the miasma theory, which held that cholera was borne by noxious smells in the air, was so persuasive in the mid nineteenth century despite mounting evidence that the disease was borne by water. I won’t go into it here but he spends quite a few pages examining this conundrum, including an in-depth look at the way the human brain is wired.
The basic story of Dr John Snow’s struggle and his famous map is interesting enough to bear retelling but what really makes this book fascinating are the frequent back stories about the underlying social, health and engineering challenges facing Victorian England.