A new study shows that our microbial companions may play a significant role in the process of our evolution. Evolution can be defined as the change in the gene frequency of a population over time. Key to the process of evolution is natural selection. Natural selection is when certain heritable traits impart a greater chance of survival and reproduction for individuals that have said traits than individuals without, under prevailing environmental conditions. A new twist on these concepts is the hologenomic theory of evolution. This theory proposes that the object of natural selection is not just the individual organism but includes the microbial communities that are associated with them. To test this theory University of Vanderbilt associate professor of biological sciences Seth Bordenstein performed research using three species of the wasp Nasonia. Two of these species were closely related and had only diverged from each other around 400,000 years ago. The third wasp was much more distantly related. The two closely related wasps had similar microbiomes while the third had a microbiome very different from the other two. These three wasps were crossbred and the viability of the hybrid offspring were observed. The resulting hybrids of the closely related wasps had a low mortality rate and had microbiomes similar to the parents. The hybrids of the distantly related wasps and either of the other two wasps had a mortality rate of near 90%. When the microbiomes of these hybrids were examined they appeared completely different to those of the parents. To test whether the high mortality rate in these hybrids was due to their microbiome, wasps were raised in microbe free environments. These germ free hybrids survived as well as purebred larvae. When germ free hybrids were given gut microbes from regular hybrids their survival rates plummeted. This shows that a species microbial community has a large impact on the viability of its offspring and is an important factor is the process of speciation. In a way you are yourself because of the microbes you carry.