Liam Heneghan in the Los Angeles Review of Books:
I am writing in a coffee shop. Ostensibly, there is only one species in this crowded room, a medium-sized primate with a penchant for disruption. But knowing a thing or two about species diversity — I am a zoologist by training — I realize there are more species in the room than meet the eye. For now, though, think of each human as an ecosystem of sorts, complete with its native cells, tissues, and organs, and think of the non-human organisms as non-native invasive species.
Put to the back of your mind images of those pestiferous insects and microbes that inhabit the pantries of every coffee shop on Earth. Also ignore thoughts of the family of mice scrambling for crumbs under the counter. After all, the bewildering diversity of organisms invading the primate body is unsettling enough, so let’s stick to these “invasives.” Amoebae glide over cankerous gums, armies of micro-invertebrates storm the hairier and damper alcoves of the body, and the skin itself is as coated with bacteria as a commode in a gas station. Inside the body, the species count is impressively high. Up to 1000 bacterial species inhabit the gut. Many are not casual hitch-hikers but essential to health, metabolizing nutrients and synthesizing key vitamins. To be sure, among the invading hordes are a few bad eggs. Plague, for example, is ghastly. And smallpox is to be avoided. But most cause nothing more than the sniffles, a mild rash, or a headache. Nothing to be too alarmed about — and, after all, you deserve that day off work.
Despite the outright helpfulness of some members of our bodily menagerie, and the fact that many of the others felicitously augment diversity, we have declared an all-out war against microbes. All because of a few bad eggs! Rather than vilifying these aliens as intruders, I argue that it is now time to embrace them as the key to our salvation.