The average human body has about 90 Trillion bacteria living in and on it (give or take a few dozen Trillion), and there are new species hopping aboard every minute of the day. Essentially, you are a biological train hurtling forward through time, collecting and depositing passengers on a regular basis.
So the question may have occurred to you, after catching a cold from your child or having your dog slobber all over you after licking his own genitalia for half an hour, which is dirtier? Which one of these creatures contributes more to your personal biome?
The answer, surprisingly, is the dog.
A new study led by the University of Colorado at Boulder looked at the type and transfer modes of microbes in the gut, tongues, and palms of 60 different American families and their pets, as well as their feces.
What they found was that the microbial connection was stronger between pet and owner than between owner and child.