Bacteroidetes: are the most prominent gut microbes in much of the world. They are thought to help protect against obesity because they do not digest fat well. The first settlers of Europe needed to be able to better digest fat, so they would have enough energy to survive brutal, Ice Age winters. People who had fewer Bacteroidetes and more fat-digesting Firmicutes therefore became the dominant players. Now Bacteroidetes are underrepresented in the guts of Europeans and North Americans, but the phenomenon doesn’t appear to be genetic. African Americans’ proportions of are more similar to fellow North Americans’ than they are to native Africans’. Fortunately, this fact means that with dietary and lifestyle changes, we should be able to grow our Bacteroidetes back especially since most of us don’t need to store up for the next saber-toothed tiger hunt. (source Ubiome).