The idea that a person can be invaded by other human cells, which then go on to live and probably reproduce in the host body, following their own hidden agenda, is a reasonably disconcerting one. However, we’ve known for a long time this happens, and not just freak accidents like a twin getting absorbed in the womb; fetus cells often cross the placenta and take up residence in their mother’s bodies, and remain there for the life of the mother.
The easiest way to detect this is to look for y-chromosomes in women – if there is one, it’s due to microchimerism, where there are some male cells living in the female body. But now there’s this: Male microchimerism in women without sons: quantitative assessment and correlation with pregnancy history. This study found that one in five women were male microchimeric, which is a huge figure even if it’s skewed by women who had induced abortions (where one in two are male microchimeric).
We can infer some things from this. First, total microchimerism is probably double that reported, since there’s no real reason to assume that male cells are better at colonising a mother’s body than female cells, they’re just easier to detect. If we assume there is no greater tendency to abort male fetuses than female fetuses, we can also infer than effectively everyone who had an induced abortion is microchimeric and carries with them the cells of the fetus. This is the sort of creepy detail that can lead to b-grade horror sci-fi stories, but it can also be considered beautiful and romantic: No fetus really dies, it lives on within the mother. There’s also a high chance that any dead child continues to live in the body of its mother. I guess it depends on your point of view.
However, perhaps the most interesting result from the study was that of the women who had only had daughters 8% were male microchimeric, and the nulligravid (never-pregnant women) had a rate of 10% of male microchimerism. There are two ways to look at this. The first:
Sperm is alive. It is living cells. When it is injected into you it swims and attaches and burrows into your flesh. If its in your mouth it swims and climbs into your nasal passages, inner ear, and behind your eyes. Then digs in. It enters your blood stream and collects in your brain and spine. Like something out of a sci-fi movie.
This rather frenzied interpretation is the result of the conclusion stating: “Besides known pregnancies, other possible sources of male microchimerism include unrecognized spontaneous abortion, vanished male twin, an older brother transferred by the maternal circulation, or sexual intercourse.” Again, some people may consider it romantic that women carry around the living cells of the men they sleep with, and it gives a whole new meaning to the phrase “he got under my skin”. However, I think it unlikely that sperm manage to invade and survive in a woman’s body considering that: a) It’s a very hostile environment for sperm, and b) If the sperm don’t join with an egg cell they die in a few days. They can’t reproduce on their own because they only have one set of chromosomes.
So the second point of view is that all of those “freak accidents” that cause microchimerism that we think are so rare, like a vanished twin or maternal circulation, are actually far more common than we thought. Not just in women, either – a lot of these can apply to men too.
If you’re sitting around a campfire late at night this might raise other questions as well, such as: What does it mean for how we view an organism? Does it change our sense of self? Does it count as “consuming human flesh”?
(Here’s a story about Evil Sperm)