You carry your mothers’ cells in your body and she carries your cells in hers. This is what researchers at the Fred Hutchinson Cancer Research Center in Seattle reaffirmed when they found pockets of male DNA (characterized by a Y chromosome) in the brains of 18 out of the 26 women studied. Scientists have long known that there is cellular exchange between mothers and their fetuses during pregnancy, leading to foreign cells present in the blood, liver, heart, and other organs of the mother many years after the fact. However, scientists were surprised to find that these foreign cells are able to cross the blood-brain barrier which acts like a wall in order to prevent foreign bodies from entering the brain. Preliminary results also seem to suggest that fetal cells integrating themselves into the mother’s brain can actually be beneficial since women who had Alzheimer’s also had less foreign DNA in their brains. These results are not yet conclusive. Still, it is reassuring to know that we are all guilty of clinging to our mothers in a way that is much more profound than a daily phone call—and this is not necessarily a bad thing.  What is the distinction between preliminary observations (ie. the correlation between foreign DNA in the brain and Alzheimer’s) and accepted findings? How much evidence is necessary for a theory to become accepted as fact?