Next time you are waiting for your turn at the dentist's chair, why not let your mind wonder about something more appealing? Here’s a relevant topic: A long time ago tooth decay was a rare occurrence. Our early relatives, including the Neandertals, hardly ever had caries. In fact, we may owe our regular trips to the dentist not to unhealthy eating habits but to recent changes in the bacteria inhabiting our mouths—and maybe even to rats!

You could be forgiven for thinking that tooth decay is an inevitable fact of life; even ancient Egyptians practiced dentistry. But the study of human teeth suggests that before our ancestors started cultivating plants for food, cavities were uncommon. Tooth decay, it seems, spread once we changed to an agricultural lifestyle.

New evidence from Omar Eduardo Cornejo Ordaz, a postdoctoral research fellow at the Stanford School of Medicine, and his colleagues back up this hypothesis. They analyzed the genomes of several strains of the prevalent caries-causing bacterium, Streptococcus mutans, to determine when new genes evolved in this species and its close relatives. The team's statistical analyses suggest the bacteria's population started expanding exponentially about 10,000 years ago, which coincides quite nicely with the birth of agriculture.

But how did agriculture spark a tooth decay revolution? Cornejo Ordaz thinks that even though agriculture brought us improved living conditions, it also brought humans and rats into much closer proximity than before. According to Cornejo Ordaz, the species most closely related to S. mutans is Streptococcus ratti, and its “natural environment is probably the rat's mouth. It is easy to imagine,” he says, “that when population densities increased after the origin of agriculture, there was increased possibility for a host shift and development of a new species."

Other researchers agree that a switch to agriculture proved damaging to the dental health of several societies. George Armelagos, an anthropologist at Emory University, studied the teeth from 39 fossil skeletons found in Wadi Halfa, Sudan, estimated to be between 8,000 to 11,000 years old. Their findings, published online December 10 in Molecular Biology and Evolution, suggest that when the Nubian people living in northern Sudan and southern Egypt switched to intensive agriculture, the incidence of caries in the population jumped from 0.8 percent to nearly 20 percent.

Not all researchers agree with the rat hypothesis, however. Peter Brown, a paleoanthropologist from the University of New England in Australia, thinks the emergence of tooth decay relates to sugar in the human diet. “You need to think about the distribution of rats and caries, both in terms of geography and through time,” Brown says. “In Australia caries came with the introduction of sugar and flour to Aboriginal communities. In Japan, during the Edo period, the samurai class had relatively poor oral health (sugar and refined carbohydrates) but the common people had a very low caries incidence (no access to sugar or refined carbohydrates)—nothing to do with rats.”

Something to ponder as the dentist’s drill descends.

10 Comments

1. 1. Jean 12:37 PM 2/6/13

   Caries are cavities

   Reply | Report Abuse | Link to this

2. 2. Sherris in reply to Soccerdad 01:47 PM 2/6/13

   Was it faster to write and post that comment than it would have been to look it up on, say, Wikipedia?

   Reply | Report Abuse | Link to this

3. 3. jduringer in reply to Sherris 02:39 PM 2/6/13

   Was your comment relevant to the article? Effective in enlightening Soccerdad to more efficient resources? Only he could say.
   
   Soccerdad, be not abashed in thine ignorance ;-). I celebrate your reading of the holy script of SA and your brief query of the community.
   
   Rock on. Enough of our digression, the caries/sugar connection is a bigger factor, IMHO. Nevertheless, the species hopping of a microorganism bit is pretty cool: a new species, though more parasitic than symbiotic. Anybody got other examples of it?

   Reply | Report Abuse | Link to this

4. 4. Carlos Solrac 02:53 PM 2/6/13

   The author of the article should read the Chapter 38 Oral and Craniofacial Diseases and Disorders by
   Douglas Bratthall, Poul Erik Petersen, Jayanthi Ramanathan Stjernswärd, and L. Jackson Brown.
   
   Below there is a paragraph of it:
   
   Dental caries develops by the localized dissolution of the tooth hard tissues, caused by acids that are produced by bacteria in the biofilms (dental plaque) on the teeth and eventually lead to "cavities." The biofilm consists of microorganisms, including the highly cariogenic mutans streptococci, and a matrix made up mainly of extracellular polysaccharides. The destructive acids are produced when fermentable carbohydrates (sugars) reach these biofilms, each episode resulting in tooth damage (attack). If this process does not occur frequently, then the natural capacity of the body (through saliva) to remineralize will prevent formation of a cavity.
   
   Therefore caries are caused by frequent sugar intake. This may be news to many; but Dr L. Jackson Brown published an uncontested scientific paper making it clear more than twenty years ago.

   Reply | Report Abuse | Link to this

5. 5. Sherris in reply to jduringer 04:48 PM 2/6/13

   Obviously in your eyes my curiosity is worth less than others'. It must be because the answer to my question isn't readily available in 5 seconds of Google searching.

   Reply | Report Abuse | Link to this

6. 6. ssm1959 06:35 PM 2/6/13

   Bear in mind the necessary interaction of Host-Pathogen-Environment for disease to occur. Bacteria are opportunistic and will not colonize new hosts unless the environment is favorable. It is reasonable to presume that as diet changed with the development of agriculture so did the constituents of oral biofilms.
   
   The authors citing of Dr Browns research really does not counter the argument regarding the origin of S. Mutans. Many isolated native populations have experienced significant grace periods between the arrival of refined carbohydrates in their diets an the onset of disease. During and immediately after WW2 sugar in large quantities was made available to ALaska natives. Sugar use skyrocketed in their diets yet for several years it appeared there was no increase in caries. In fact a few researchers had proposed that ALaska native may be the only people on the planet who were naturally immune.
   
   However shortly after this, decay exploded in these populations. The increased communication with the outside world brought not only the sugar but also people who were carrying the flora necessary for caries. The Native "caught " tooth decay just like you might catch a cold.

   Reply | Report Abuse | Link to this

7. 7. chubbee 06:24 AM 2/7/13

   Perhaps the short pre-agricultural lifespan of our species played a roll in the presence of tooth decay as well

   Reply | Report Abuse | Link to this

8. 8. S. N. Tiwary 08:19 AM 2/7/13

   Now-a-days, teeth decay is common. To know the exact reason for decay is extremely important for everybody because almost everybody is suffering from this.
   The present article is very useful for all.
   S. N. Tiwary
   Director

   Reply | Report Abuse | Link to this

9. 9. Jason Lewis 04:39 AM 2/14/13

   Interesting theory
   but In my opinion our <a href="http://portalada.com.au/ADA_CPD" title=""> Dental health</a> is nothing to do with rats.
   Statistical data given above is may be relatively true to some aspects.
   I appreciate the efforts of our scientist to find out something immeasurably small.
   It was informative and interesting
   Thank you
   

   Reply | Report Abuse | Link to this

10. 10. Raiken3712 02:21 PM 3/3/13

    http://www.jackkruse.com/brain-gut-6-epi-paleo-rx/
    
    A paleo diet without the grains greatly reduces the sugar. Grains and starchy vegetables break down into sugar. Sugar that feeds the bacteria and this diet also wrecks the bacterial balance in our bodies.
    
    A healthy bacterial system includes the right balance of bacteria which is messed up by a diet rich in sugar including grains and starchy vegetables.
    
    Raw milk is a great bacterial source and rawmilk.com has plenty of good information on it.
    
    westonaprice.org is another good source of information for keeping strong teeth as well as Ramiel Nagels Youtube videos on Curing Tooth Decay

    Reply | Report Abuse | Link to this