HIDDEN GUESTS

Published in the Nov. 29, 2025 issue.

While you’re sitting at the table this Thanksgiving, say a few extra blessings for those whom (you think) are not present. 

Because they just might be. 

Read Lise Barnéoud’s “Hidden Guests” and you’ll be convinced of it. 

As pediatrician and geneticist Judith Hall wrote in 2003, “So you think your mother is always looking over your shoulder? She may be in your shoulder.” 

How? Via microchimerism. 

Microchimerism concerns the exchange of cells between a mother and fetus during pregnancy. Because it turns out the placenta is a two-way highway, allowing the migration of cells — cells that are able to assimilate into a new host.

Cracking open this little door, as Barnéoud lays out, creates a whole hallways of new doors and possibilities. Cells from your grandmother can conceivably have continued to hide away and multiply somewhere in your mother’s tissue for decades before migrating to you. 

*If you think this implausible, researchers have found that a line of immune cells survived over 51 generations in mice. In human terms, 51 generations = 1,000 years. 

Cells from your mother’s miscarriages, your unknown brothers and sisters, could (and have been proven) to end up in your body. 

In one mind-bending case, a woman named Karen Keegan discovers that her children’s DNA does not match her own. How? 

“She [Keegan] was destined originally to be fraternal twins. Both of the original fertilized eggs were girls. And so when these fertilized eggs – which presumably, because they were close to each other in her mother’s womb, or for reasons we don’t understand yet, fused at a very early stage of development – she developed with two separate cell lines. This dub le cell lineage extended to her ova: some matched her genetic profile while others originated from her vanished twin.” 

So she literally gave birth to her nephews, who had a mother who never lived. 

Of course, there are instances outside of pregnancy which also involve an exchange of cells. In one chapter, doctors discovered that a man from Reno who’d had a bone marrow transplant was slowly having his body being taken over. 

“DNA analyses would show that his cells were being depopulated and that cells with another genetic signature were emerging in their place. This strange substitution began in his blood, then spread to the insides of his cheeks and his saliva. One day, they found this new genetic signature in his semen … “ 

This led to a whole discussion about the efficacy of DNA evidence. Another chapter discusses the possibility that women may harbor the cells of former sexual partners. 

“It’s a mistake to think of ejaculate as nothing but sperm, which makes up just 2-3% off seminal fluid. The rest is proteins, sugars, hormones and other cells, including immune cells – cells that could make a break for it once they’ve entered the body.” 

Then consider that in one study of 54 deceased women, 63% had male cells in their brains.

“It showed neither where these cells came from nor whether they were neurons or one of the other types of cells that populate our brains. But it did make one thing clear: microchimeric cells can cross our blood-brain barrier.” 

One researcher’s suggestion: “If you don’t want to wind up with a head full of cells from multiple men, you’d better use protection.” 

Now how’s that for a Thanksgiving message from The Sheet!