The presence of the DNA persisted into old age and correlated with a slightly decreased risk of Alzheimer's disease. No word on behavior changes, but there's a joke in there about football or another hilarious but not-too-sensitive gender normative topic.

DavidDuprey/AP

PROBLEM: We know of relationships between parity (bearing children) and likelihood of developing certain diseases later in life, but the mechanisms are unclear. Studies with mice had shown that DNA of a fetus can cross the blood-brain barrier and get into the brain (suggesting involvement in neurologic effects), but it hadn't been shown in humans.

METHODOLOGY: Researchers out of the University of Alberta looked at autopsy specimens of the brains of 59 women (ages 32 to 101). They used PCR to scan the brain tissue for a gene that's only found on the male Y chromosome. The women's histories of pregnancy weren't available to the reseachers.

RESULTS: Male DNA was present in 63% of the female brains. It was distributed throughout the brain, not just in a particular area, and across all ages.

CONCLUSION: Male DNA is often found in the brains of women -- reasoned by the researchers to be a remnant from pregnancy with a male fetus -- and remains present into old age. That would mean fetal DNA is able to cross the blood-brain barrier, which hadn't been demonstrated before in humans.

