Bacteria are a crucial part of human digestion. Hundreds of billions of them live in our stomachs and intestines, many helping us digest food. With the many different kinds of bacteria, and the many different types and habits of people, it would seem like each stomach and intestines would be unique - a less poetic metaphor for human individuality than a snowflake, but a more apt one. This, however, is not the case. We're far more uniform inside than we are outside. Human gut bacteria ecosystems fall into three different types: Bacteroides, Prevotella and Ruminococcus, each named for the bacteria that rules the roost.
Scientists believe that the reason for this conformity is that our guts can only configure themselves into a limited number of habitats for bacteria. In one habitat, one type of bacteria can dominate - in another, they are forced into a more niche group. Three different gut types is all that humanity can muster.
The ruling bacteria may influence our bodies, too. Gut types have been associated with different physical and medical conditions in people. A recent study found some bacteria process food more efficiently than others - this leaves more calories for their human hosts, and so they may have trouble losing weight. Another study found a correlation between certain bacterial strains and diabetes.
So do our stomachs create us or do we create them? Scientists aren't sure yet. All they've found is correlation - with no word on cause. They also don't know if people could change their gut ecosystems through diet, exercise, or medication.
