More on this book
Community
Kindle Notes & Highlights
Human “gynecology,” at each stage of its evolution, also includes many types of birth control, abortion, and other fertility interventions.
While genes go about the business of trying to perpetuate themselves, female animals are also generally trying to stay alive.
If you put a pregnant mouse in an enclosure with a male who isn’t the father, she’ll abort (this is called the Bruce effect
recognized the Bruce effect in the 1950s, researchers started finding it all over the mammalian world.
But we humans don’t. And that’s rather telling.
But even more tantalizing, for our purposes, is the fact that no gelada male will successfully rout a dominant male without the support of that male’s current sexual partners.
After running blood tests on wild herds, scientists determined that roughly a third of foals aren’t sired by the dominant stallion.
Abortion is just one of the things that female mammals do.
If anything, the fact that human women don’t have long-evolved internal mechanisms to support female reproductive choice is what’s unusual.
Apparently, 5 percent of American rapes result in pregnancies.
That might not sound like a lot, but the chance of pregnancy resulting from a single bout of intercourse on your most fertile days is only 9 percent, with that chance dropping to near zero on non-fertile days.
Why human women have so many miscarriages after the egg implants in the womb may also have little to do with the partner. Most miscarriages occur in the first thirteen weeks of pregnancy, and even more commonly in the first eight.
And most of them seem to be due to chromosomal abnormalities. That means one of two things: either the egg or the sperm already had some genetic issues, or at some point in early cellular division something went wrong.
Ancient hominins just weren’t all that rapey. If they had been, women would probably have fancy vaginas, men would have hi-tech penises, and women would have a more reliable miscarriage response to rape and male threat.
Homo erectus males stood a full five feet ten—a good inch taller than the average height of today’s American men.
Erectus a tool user, but also she was the first hominin to take down big game and the first to use fire.
Erectus improved on Habilis’s tool tech. She invented the Acheulean tools: long, thin, elegant hand axes and choppers.
Despite making it out of Africa and colonizing a number of places, leaving fossils and her stone tools along the way, Erectus went extinct over time.
creatures who aren’t prolific reproducers hit environmental and competitive challenges and, lacking suitable work-arounds, they fail to adapt.
Maybe that’s why as few as 50 percent of human pregnancies actually produce a human baby.
This is the first record we have of the hominin success story: the fact that our Eves were able to adapt to a wide variety of new environments.
By one recent calculation, the MVP for a reproductive group of humans isolated for 150 years would be fourteen thousand, with forty thousand being a much safer bet.
minimum viable population
In other words, for each transition point in humanity’s ancient migrations, you should expect to find a group of skinny, scrappy people just barely producing enough kids to replace themselves, finding ways around the inherent problems of inbreeding, and miraculously surviving.
the placenta regulates a pregnant mother’s immune system, as it does for most mammals. But it’s especially true in the human body, where our extra-invasive placenta has to work extra hard to hold its ground. Evolving ways to make the maternal immune system look the other way makes perfect sense for the embryo, because in the trench warfare of maternal-fetal competition, you really do want to strip the enemy of its bigger guns as soon as possible.
In places where malaria is endemic, a full 25 percent of all maternal deaths can be directly tied to malaria. Pregnant women are three times more likely to suffer a severe version of the disease, and nearly 50 percent of those women will die.
Thinking about malaria as a gynecological problem—not simply that women and fetuses are “vulnerable,” in other words, but that human pregnancy might be an important feature of how the disease works in a larger mixed-sex population—requires a similar shift.
If something like malaria uses human placentas as reservoirs, hiding from the mother’s immune system, what could we accomplish by offering women safe, healthy choices about their reproductive destinies?
When, in other species, physiological evolution would have created a newly evolved feature to enable female reproductive choice, hominins used behavioral innovations instead—some of them social and others involving new tools and pharmaceuticals.
That control we have over the most powerful levers of our evolutionary fitness got us to where we are today. It allowed the early human population to finally explode, expanding into nearly every ecological niche our ancestors stumbled upon.
The symbols of our ultimate technological achievements shouldn’t be the atom bomb, the internet, the Hoover Dam. Instead, they should be the Pill, the speculum, the diaphragm.
Most do assume tool use is a fundamental trait in the primate line, which does imply some sort of “hard wiring,” but its arrival wouldn’t be as obvious as the expansion of the visual centers of the brain.
Fire came into widespread use some half a million years after Habilis chipped away at her rocks
It’s possible that bargaining of that kind—a bit of a nutrient-dense placenta in exchange for protective and assistive behavior—could be part of how hominin midwife culture got started.
In general, the hominin evolutionary line has progressively less sexual dimorphism—the closer you get to Homo sapiens, the more similar the sexes’ body size.
what’s rarely mentioned is that, for Homo sapiens at least, having too many pregnancies spaced too closely together—particularly if those pregnancies come to term—significantly increases the complication and mortality risk for both offspring and mother
This effect occurs in pregnancies less than thirty-six months apart: less,
That’s a large part of how malaria does so much damage to the body’s organs: it gums up the works in delicate blood vessels. Because placentas are especially rich with small blood vessels, that may also be part of how the protozoan ends up there.
book—a book about the evolution of sex differences.
the oddest thing about our species might be that the female human brain doesn’t seem to be all that functionally different from the male.
Adult human “female” brains are remarkably similar, in nearly every way one can measure, from cellular structures to outward function, to adult “male” brains. That’s not true of rodents: male rodents have distinctly rodent-masculine brains, and the females have pretty obviously female brains; both are clearly about the same size, proportional to their bodies, but the way a female rodent’s brain reacts to something like a particular pheromone is drastically different from what a male brain does.
why aren’t most women’s brains more functionally different from men’s?
The IQ scores of boys and girls up to age fifteen are about equal. But at puberty, boys start to have slightly higher mean IQ than girls, implying that grown men are naturally “smarter” than women. If that’s true, then the “Female Brain” might really exist—or start to exist—somewhere around puberty.
Right now, most researchers think IQ is anywhere between 50 and 80 percent heritable, and the latest research proposes that it’s closer to 80. That does
For one thing, white Americans tend to have higher IQ scores, on average, than African Americans. But if you control for family income, most of those differences disappear.[*5]
The bell curve of IQ test results for any group of human beings tends to have a long tail in either direction.
The same can be said for the differences between the scores of men and women. The average woman and the average man will both tuck themselves neatly under the big hump of that curve.
Where you tend to find the most difference is at the tails. That’s why the mean shifts for men—they have wider variability overall, but this shows up in some areas more than others.
For example, if you isolate those things we call mathematical ability, male test takers have far more variability than females, with more male geniuses on one end of ...
This highlight has been truncated due to consecutive passage length restrictions.
On many measures of quantitative and visuospatial ability, men and boys have more spread in their results.
