Bringing the pieces of the puzzle together seems to show what I call the ecological theory of disease. This is the idea that illness can arise from the presence of species that negatively affect our health or the absence of species that positively affect our health.
Of course, to ecologists and evolutionary biologists, such a theory is not exactly news. We can all hold up long lists of species that require other species, their partners and neighbors, to survive. Think corals, lichens, leaf-cutter ants, tube worms, bean plants. Now think humans. Take away the species we benefit from every day and we would die in many different ways.
The point is that public-health researchers, medical researchers and doctors don't think like ecologists. Hospitals only consider other species when they are "bad," when, that is, they are behaving as germs. With a couple of examples we tend to regard as freakish (the medical use of leeches or fly maggots), doctors almost never prescribe the apple, bacteria, worm, or other sort of "nature" your body is "missing," though if you took just the right mix it would surely help keep the doctor away.
So what should we do? If the germ theory of disease tells us to hunt down, scrub off and otherwise avoid bad species, the ecological theory of disease suggests the same, but that we also need to figure out how to attract, farm, and nurture beneficial species. Fine. But there is a big problem: While we have spent the last 200 years chasing down bad species, we have spent far less time hunting good ones. Worse, while there are hundreds of pathogens that affect our health and well-being (with a small handful being the really deadly monsters), the precise mélange of beneficial species we need could involve hundreds of thousands of species—or more.
Those species do not always have names. Recently, I cataloged the species on my body and my house, finding more than 2,000 species, most of which most experts could not identify. Which ones were good for me? Who knows? What is worse, no one could tell me which good species I might be missing.
More and more, we seem to "know" that we need nature. Many of its species benefit us, but we are not yet smart enough to know which ones. We are left to wait for the systematists—those catalogers of life—to find and name the species on our behalf. And then we will have to wait some more for the ecologists and evolutionary biologists to study those species. Only then, finally, will medical researchers begin to weigh up which ones we need and which ones we don't. But it will take a while.
We have neglected the book of life for so long that at our current rate of research, without investment in projects larger than any yet imagined, much less implemented, we won't catch up for hundreds of years. Meanwhile, some of the species we are losing from forests and wild lands (or just from our modern lives) could easily be the ones that help to make us whole.
If we only knew which ones.
This article originally appeared in New Scientist.