Though you're born with an entirely sterile digestive tract, your guts fill with microbes as you grow up. In fact, these gut bugs outnumber your cells 10 to 1. And every species grows its own unique group of microbes.
In fact, a study published today in PLoS Biology shows that our gut fauna are so unique that you can identify a creature's species entirely by analyzing the output of its digestive tract.
This new study flies in the face of the idea that you are what you eat, a truism which has defined scientific thought on where we get all those microbes from. Previously, it was believed that the creatures in your gut were determined by the foods you ingest and where you live. But in fact, it's your species that determines it. No matter where people live, and what they eat, they tend to have the same microbes in their waste. PLoS Biology summarizes:
[Howard] Ochman and colleagues found that diversity in the composition of these gut communities, not including those occasional transients and unwelcome visitors such as pathogenic bacteria, depends primarily upon the host species.
Using genetic markers, the team measured the diversity and abundance of various microbial species found in fecal matter of five great ape species collected in their native ranges and discovered that bacterial populations assorted to species. Moreover, the relationships of the microbial communities matched that of their host. In other words, not only is it possible to differentiate chimpanzees from humans by examining the microbial populations within their guts, but these gut microbes have been tracking the evolution of their hosts for millions of years.
That's right: If Gaius Baltar really wanted to know the difference between human and cylon, he could have done it just by analyzing stool samples.
via PLoS Biology