third trait that evolved in S. mutans is its ability to not only survive, but also thrive in acidic conditions. This trait gives S. mutans a selective advantage over other members of the oral microbiota. As a result, S. mutans could outcompete other species, and occupy additional regions of the mouth, such as advanced dental plaques, which can be as acidic as pH 4.0. Natural selection is most likely the primary evolutionary mechanisms responsible for this trait. In discussing the evolution of S. mutans, it is imperative to include the role humans have played and the co-evolution that has occurred between the two species. As humans evolved anthropologically, the bacteria evolved biologically. It is widely accepted that the advent of agriculture in early human populations provided the conditions S. mutans needed to evolve into the virulent bacterium it is today. Agriculture introduced fermented foods, as well as more carbohydrate-rich foods, into the diets of historic human populations. These new foods introduced new bacteria to the oral cavity and created new environmental conditions. For example, Lactobacillus or Leuconostoc are typically found in foods such as yogurt and wine. Also, consuming more carbohydrates increased the amount of sugars available to S. mutans for metabolism and lowered the pH of the oral cavity. This new acidic habitat would select for those bacteria that could survive and reproduce at a lower pH. Another significant change to the oral environment occurred during the Industrial Revolution. More efficient refinement and manufacturing of foodstuffs increased the availability and amount of sucrose consumed by humans. This provided S. mutans with more energy resources, and thus exacerbated an already rising rate of dental caries. Refined sugar is pure sucrose, the only sugar that can be converted to sticky glucans, allowing bacteria to form a thick, strongly adhering plaque. See also Mutacin 1140 Oral microbiology Streptococcus viridans'' Xylitol Caries vaccine References External links MCHoralhealth.org Type strain of Streptococcus mutans at BacDive - the Bacterial Diversity Metadatabase Streptococcaceae Gram-positive bacteria Bacteria described in 1924