Tag Archives: ecology

Emerging Diseases and Forest Fires

I have been interested in emerging diseases ever since reading The Hot Zone by Richard Preston, which was so intense that it kept me awake during an entire overnight train ride from Boston to Washington DC. So I was very psyched at Christmas to receive a copy of Spillover by David Quammen. I just finished it, and know a lot more now about how diseases jump from animals to humans.

Scary cover, great book!

Scary cover, great book!

Quammen uses the book to explore theories about why there seem to be more frequent incidents of humans being infected by animal diseases (think SARS, Ebola, Hendra, Avian Flu, etc.). One of the theories he discusses concerns how increased human development is breaking up large contiguous ecosytems into smaller ecosystems separated by cities, farms, etc.

For example, a large forest might be full of bats that could be carriers of some nasty virus. This forest contains metapopulation of bats, or a series of smaller populations that meet and mingle at their edges. In a metapopulation an infection is likely to be constantly present, but at a low level of incidence. If each smaller population becomes isolated, however, that population will likely go through a boom and bust cycle of infection, with periodic epidemics infecting most members of the population.

If that highly infected population runs into humans, there is increased likelihood of the infection passing to the humans. In other words, if 90% of bats are infected, then there is a higher probability of bats passing their disease to humans than if only 10% of bats are infected.

As development has broken up formerly vast forests into smaller forest segments surrounded by cities and suburbs, we have seen metapopulations of natural disease reservoirs (bats, rats, mice, etc.) broken up into the isolated populations that are more likely to transfer diseases. Hence the increasing number of obscure infections jumping into humans.

What struck me about this theory is the parallel to forest fires. Current wildfire thinking holds that if you put out wildfires, fuel loads will build up and eventually you will get a catastrophic fire that can’t be controlled (like the 2002 Biscuit Fire in Oregon, which burned nearly 500,000 acres; I drove through the edge of that fire, and the smoke turned day into night). But if you let natural fires burn, they will clear out the fuel load and not turn into conflagrations.

So you can have small, more frequent fires, or rare, catastrophic fires. Much like you can have frequent, low levels of infection in your animals, or rare, but massive levels of infection. And in both cases, human intervention in the environment is what moves things from low-level balance to a high-level cyclic system.


Mother Nature vs. Capitalism

I was recently reading a transcript of a speech that theologian Sallie McFague gave on religion and ecology. In the speech McFague works her usual metaphor magic, discussing how language drives thought, and thought drives actions. Specifically, she called for a reimaging of the Christian worldview, from one in which the world is seen as a thing, a machine in which humans live, to one in which the world and the humans therein are seen as shared parts of a holistic body of God. This view – “that the world is from the beginning loved by God and is a reflection of the divine” – would forefront the inherent value of the environment and the religious importance of its conservation.

Interestingly, McFague claims that this reimaging is not new, but instead a return to a traditional worldview, held by Christians and non-Christians alike. The concept of earth as machine, she claims, “is an anomaly in human history, for until the scientific revolution of the seventeenth century, the earth was assumed to be alive, even as we are.” McFague is not calling for a return to pre-scientific thinking, in which we must appease tree spirits and illnesses are caused by foul humours (although the current use of medicinal leeches is totally cool), but rather a recognition that all of creation is equally part of God.

For McFague, the culprit is less the scientific revolution than the drive toward individualist consumption that the market economy has engendered. Consumption of goods is linked to consumption of the earth’s resources.

“From the time of Aristotle to the eighteenth century, economics was considered a subdivision of ethics; the good life was understood to be based on such values s the common good, justice, and limits. Having substituted the insatiable greed of market capitalism in place of these values, we are now without the means to make the qualitative shift in thinking that is required.”

While I would not be inclined to say “insatiable greed,” there is no question that a market economy is inherently consumptive and that it drives people to focus on the individual rather than the common good. McFague would have us work within the current system, but temper its impact on our behavior by changing how we think and speak about the world.

To McFague’s argument from metaphor I would only add that it’s not nice to fool mother nature.