We owe it all to our moms

Besides teaching us how to eat, talk, use the bathroom, get dressed, and interact with people, moms probably do a lot more for us as well.  Some studies of IQ suggest that the environment in the womb may have a more important affect on IQ than our genetic make-up, and we know that toxic substances in the womb may really cause a lot of problems in the development of an infant.  It turns out that the environment of the womb and the environment experienced immediately after birth may have a huge effect on the composition of our gut flora as well.  Just as all people have unique fingerprints, all people have unique gut flora. No one is sure yet why our gut microbes are different, but it is starting to look like it depends on our mothers.  Twins, (both identical and fraternal) have gut that are more similar to each other than to other people, including parents or siblings.  If only identical twins had this similarity, then it would seem that genetics of the individual determine gut flora, but since fraternal twins have gut flora more similar to each other than everyone else, the shared early environments in the the womb and shortly after birth are the most likely sources of variation.  

Why is this important?

Gut flora composition has been implicated as a factor in obesity, colitis, irritable bowel syndrome, and other gut related disorders.  Cultivating a healthy gut flora in early infancy may help a person have better health throughout his/her entire life.

That said, don't go blaming your mom for all your gut problems (should you have them).  There are measures we can take on our own to have healthy gut flora.  We can eat complex carbohydrates such as those found in vegetables and whole grains.  We can also eat yogurt. These types of food change the composition of gut flora towards the microbes associated with healthy people.