Our latest paper that just came out today in Nature Genetics is a bit of a departure for me (again!); I really must not take much credit for this given that it was a huge effort among a big team of people and I played a comparatively minor role. Still, I can definitely say this is one of the more interesting papers I’ve co-authored in a while.
For me the involvement started after Alan Cooper (Director of the Australian Centre for Ancient DNA) asked me for a bit of help with a cool paper he and some of his colleagues were working on. When he told me what the subject was, my initial reaction was (yawn): Dentistry? Teeth? You’ve got to be joking. Why would an ecologist be even remotely interested in that stuff? Then he went into more detail, and I was hooked.
Before I get into that detail, I have to tell you a story about a colleague of mine (name withheld, but true story) who recently went to the dentist to have some routine cleaning and maintenance done. There was nothing particularly special about his visit – no local anaesthetic, no extractions, no caps, and certainly no surgery. Two weeks later he was in the hospital theatre getting his chest cracked open for open-heart surgery. Jesus H. Christ!, I said to myself.
What happened was a tiny bit of his dental plaque was dislodged during the cleaning and entered his bloodstream through a small wound in his mouth. The bacterial plaque fragment raced around his circulatory system until it became unfortunately lodged in a tiny eddy that had developed behind one of his (slightly faulty – but he didn’t know this at the time) ventricular valves. The fragment started to grow and threaten the working of his entire heart, such that had he not had the surgery to repair the valve, he would have been dead in weeks to months. Who knew that going to the bleeding dentist (pun intended) was so dangerous? I certainly didn’t.
Back to Alan’s description of the paper. It turns out that our mouths are really disgusting places. I mean really, really disgusting, pathogen-ridden cesspits of filth. You might think you have a clean mouth, but ironically, all that modern oral hygiene combined with our spectacularly unhealthy diets dominated by refined foodstuffs means that we have rather rapidly destroyed the once-healthy bacterial ecosystem of our mouths. And most of that ecosystem degradation has come about in the last 150 years.
Our paper, Sequencing ancient calcified dental plaque shows changes in oral microbiota with dietary shifts of the Neolithic and Industrial revolutions, is a weird and eclectic mix of ancient-DNA genetics, dentistry, ecology and nutrition. Now I know the meaning of ‘transdisciplinary’! As the title implies, Christina Adler (lead author), Alan and others hooked up with an archaeologist, Keith Dobney, to identify what was in the hard dental plaque found on the teeth of ancient human skulls. Of course, ancient DNA techniques were really the only tools at their disposal, but it wasn’t until 2007 that the methods had become refined enough and the facilities isolated enough to amplify the very delicate strands of degraded bacterial DNA.
After isolating samples from Mesolithic (7550-5450 years before present), Neolithic (7400-4000 years BP), Bronze Age (4200-3000 years BP), Medieval (1100-400 years BP) and modern (today) human remains (well, the modern samples were taken from live humans – we didn’t kill them*), we found a marked decline in bacterial diversity (bacversity?) over time. The change was particularly acute after the onset of the Industrial Revolution about 150 years ago when refined sugars and flour became widely available. Another big change we noted was the increase in prevalence of specific bacterial pathogens after farming became widespread in the Neolithic, and again after the Industrial Revolution (see figure).
Now, the diet and hygiene issues aside, what is the ecology behind these changes? Well, our interpretation was that a progressively simplified diet consisting of more and more simple carbohydrates and sugars has essentially led to widespread ecosystem degradation in the mouth’s bacterial community. We know at least that in a macro-ecological context (i.e., not the mouth, but what we traditionally define as ‘ecosystems’), higher diversity generally means higher ecosystem resilience to disturbance and greater productivity (see previous posts here, here and here on this subject).
In other words, our crap diets (refined, simple) have killed off a lot of the mouth’s ‘good’ bacteria, thus leaving the path open for invasion and dominance by the ‘bad’ (disease-causing) bacteria. We have systematically simplified our natural mouth ecosystem to the point where the pathogens are winning – and they’re killing us in response. Indeed, dental caries is now a major endemic disease that affects 60–90 % of school-aged children in industrialised countries, and periodontal disease occurs in 5–20 % of the adult population worldwide (Petersen et al. 2005). But it’s not just rotten mouth diseases – nasty oral bacteria are also associated with arthritis, cardiovascular disease and diabetes. The permanent state of inflammation caused by our weakened bacterial ecosystems and the leakage of bacteria into the blood stream are doing all sorts of damage to our bodies.
So the next time some uninformed cretin tries to tell you biodiversity is nothing but a greenie waste of time, remind him that the loss of his own biodiversity has turned his mouth into a killing machine.
Now, I’ll finish up by saying that this little post is accompanied today by a bit of a media blitz, including Youtube spots and highlights coming out in Science. It’ll be interesting to see how ‘viral’ it all goes – I suspect it will be fairly popular. As a wise person once told me – media stories that involve ingestion, defecation or fornication generally get good air-time (but those weren’t her exact words – you figure it out).
*Alan tells me that some of the modern samples came from members of his lab, who all trooped over to The University of Adelaide School of Dentistry for plaque and calculus collection.