I admit, I have no evidence of an imminent Zombie attack. Maybe Invasion of the Body Snatchers would have been a better sociocultural reference. In any case, here's the news: Researchers have found male DNA in the brains of women that appears to have come from male fetuses they carried when pregnant.
Melissa Healy in the Booster Shots blog at The Los Angeles Times calls the story "astonishing," and I agree. Here is her nice, evocative lede:
For decades after a woman has carried a male child in her womb or shared her mother's womb with a brother, she carries a faint but unmistakable echo of that intimate bond: male fetal DNA that lodges itself in the far recesses of her brain.
Note the mention of an alternative explanation: The male DNA could have come from genetic scraps left around in their mothers' wombs by older brothers. It's not entirely clear to me from Healy's story how the researchers determined that some of the DNA comes from fetuses, not older brothers. The study in PLOS1 says "the most likely source" of male DNA in women's brains is being pregnant with a male fetus. I don't find that tidbit in Healy's story.
At New Scientist, Sara Reardon does quote one of the study's authors on that point, that pregnancy is the most likely source for the male DNA. And she notes that the researchers did not know which of the brains they autopsied came from women who had been pregnant. Reardon also mentions, high in her story, that the discovery could explain why Alzheimer's disease and other neurological disorders "are more common in women who have had children."
Charles Choi at Live Science gives us a clean, straight reading of the study, quoting one of the researchers to the effect that this DNA in mothers' brains has "the potential for positive and negative consequences." Whether this is a net advantage of disadvantage is not clear, the researcher tells Choi. His story also hints that DNA from female fetuses can also cross into mothers' brains, but he doesn't say so outright. It was easier, he reports, to look for male DNA and reason it came from the fetus, than to try to disentangle mothers' and daughters' DNA in brains.
If that's the case, the stories might have been a little more gender-neutral, reporting that DNA from male and female fetuses might cross into mothers' genes, even if the evidence from this study all came from males.
Melissa Lee Phillips, writing for Science Now, quotes an outside researcher saying that "the presence of fetal cells" in the female brain could prevent disease. Notice the researcher did not say "male" fetal cells.
It's an astonishing story. I don't think it presages a Zombie apocalypse. But I didn't see anyone saying it doesn't.