“It’s a killer, Bella. Look at yourself.”
“The fetus isn’t compatible with her body. Too strong, for one thing, but she could probably endure that for a while. The bigger problem is that it won’t allow her to get the sustenance she needs.”
So Bella was stronger now, but the thing was, too. You couldn’t starve one without starving the other, and healing worked just the same. No way to win.
From Breaking Dawn by Stephanie Meyer.
Ok, so what does this have to do with for realsies pregnancy? A lot.
Dr. Haig argues, a mother and her unborn child engage in an unconscious struggle over the nutrients she will provide it.
Dr. Trivers argued that families create an evolutionary conflict. Natural selection should favor parents who can successfully raise the most offspring. For that strategy to work, they can’t put too many resources into any one child. But the child’s chances for reproductive success will increase as its care and feeding increase. Theoretically, Dr. Trivers argued, natural selection could favor genes that help children get more resources from their parents than the parents want to give.
As Dr. Haig considered the case of pregnancy, it seemed like the perfect arena for this sort of conflict. A child develops in intimate contact with its mother. Its development in the womb is crucial to its long-term health. So it was plausible that nature would favor genes that allowed fetuses to draw more resources from their mothers.
A fetus does not sit passively in its mother’s womb and wait to be fed. Its placenta aggressively sprouts blood vessels that invade its mother’s tissues to extract nutrients.
From Silent Struggle by Carl Zimmer, available here.
Just as Meyer described, in real life pregnancies, the woman and the fetus are engaged in a struggle for nutrients. The fetus manipulates the woman’s body, putting her in danger sometimes, in order to get more. For example, right now, all my rage is raising my blood pressure. This is dangerous for me, but it is allowing the fetus to get more nutrients. So it’s like the little vampire inside me wants me to be pissed off all the time. I’ll remember this when he’s a teenager! Yeah, you want to borrow the car? Well, I wanted to not be on bed rest! Tough luck. (I was on bed rest for about one month with my first because of high blood pressure.)
The punchline proving Meyer’s intelligence? This is related to “imprinting,” the expression or silencing of certain genes.