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What Changes In Birthing Mean For Evolution


Do you know what time of day you were born? A lot of us used to be born in the middle of the night, but not anymore. Most babies are now delivered Monday through Friday, 9 to 5, according to a new report out by the Centers for Disease Control. What's most interesting about that report is the effect these changes in U.S. birthing culture could have on human evolution. Julienne Rutherford joins us from member station WBEZ in Chicago. She's got a pretty interesting job. She's a biological anthropologist, and she is an associate professor of women, children and health sciences at the University of Illinois at Chicago. And she's been studying this.

Thanks so much for talking with us, Julienne.

JULIENNE RUTHERFORD: Oh, good morning.

GARCIA-NAVARRO: First of all, why are so many births happening during work hours?

RUTHERFORD: Well, with a recent study and what we've known for some time, births are much more likely than they were in generations past to occur in hospitals. We're also seeing dramatic increases in inductions of labor that often results in cesarean sections. Those are medical procedures that have to be scheduled. And the - usually best time of day for the physicians performing those procedures is...

GARCIA-NAVARRO: Working hours.

RUTHERFORD: ...In the morning. Yeah.

GARCIA-NAVARRO: What effect could this have centuries from now from an evolutionary perspective?

RUTHERFORD: One of the major features of human birth is that our babies are big, so that head has to get out of the mother's body through a pretty narrow and complicated pathway. And it's different than we see in a lot of the other primates, where these heads are a much more manageable size. What we know from the clinical literature is that when you look at kind of the range of head sizes for babies, the bigger-headed babies are associated with poorer outcomes, worse birth outcomes for both the babies and the moms.

GARCIA-NAVARRO: So possibly bigger-headed babies. How could women's bodies change if this continues?

RUTHERFORD: There is some controversy about what the range of pelvic sizes really means. But certainly, it has to be big enough for the head to come through. And so if you remove the pressure of that fetal head in the pelvic dimension, then you have a wider range of women sizes.

GARCIA-NAVARRO: So maybe there might be shorter birth canals, for example.

RUTHERFORD: It is certainly something to consider.

GARCIA-NAVARRO: But does bigger heads mean bigger brains? And does that mean that we as a species might be evolving into a more intelligent species because we are intervening in that way?

RUTHERFORD: What we know from kind of current studies of human variation and the relationship between head circumference and brain size suggests that that's probably not the avenue by which our species is going to increase in intelligence. You know, we might have slightly bigger heads that measurably, you know on paper, you see this increase but biologically and certainly cognitively may have absolutely no significance whatsoever. I can assure your listeners we're not going to be producing super genius babies because of C-sections.

GARCIA-NAVARRO: Just have another question for you. Is this also wreaking havoc for astrologists working out birth charts? I'm kidding.


GARCIA-NAVARRO: I just feel like now we're just going to have to question the entire science of astrology.

RUTHERFORD: Well, you're just going to have to follow up next week with an astrologist.


GARCIA-NAVARRO: Indeed. Julienne Rutherford is an associate professor of anthropology and of women, children and health sciences at the University of Illinois at Chicago. Julienne, thank you so much.

RUTHERFORD: Thank you, Lulu. Transcript provided by NPR, Copyright NPR.