We need More Vegetables...that must be it....
In a follow-up experiment, Bercik's team corralled two strains of mice born and raised in a sterile environment: timid BALB/c mice, and NIH Swiss mice, known for their courageous, exploratory behavior. The researchers then colonized each group of these "germ-free" mice with bacteria from mice of the opposite strain. The result of this microbial swap was uncanny: The normally anxiety-prone BALB/c mice became much more fearless explorers, while the typically daring NIH Swiss mice suddenly grew more hesitant and shy. The results, Bercik says, underscore that at least in laboratory mice, some seemingly intrinsic characteristics are driven not solely by the animals themselves, but also by microbes inhabiting the gut. Whether the pattern holds up in humans, whose guts harbor more diverse microbial communities, remains to be seen, Bercik says.