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Instead of just using carbohydrates for energy as they work, mammalian muscle cells shift and start metabolizing fats and amino acids, too. That switch is a lot like the “second wind” endurance athletes talk about: when you start to get tired, but then somehow you feel energized again.
One of the big changes that happened in hominin evolution, starting—we presume—around Ardi’s time and continuing through to modern humans, is that we became “gracile”: the Eves that led to humanity evolved lighter bones and different sorts of muscles. It’s generally assumed we did this because walking upright is calorically expensive.
The fastest human can run only thirty miles an hour, and only for a few seconds.
So maybe, the argument goes, Ardi and her kin invented hominin monogamy to make the trade more appealing: that way, the guys would be motivated to bring home the bacon in exchange for a little lady waiting faithfully under the canopy.
But if females bear a greater need for food—in terms of both having pregnancies and needing to feed their offspring—then it seems safe to assume that added food pressure would be a driver in selecting for evolutionary change.
In a changing world with increasing food variability, Ardi would have had to venture farther to get enough food, and once she got it, it would have been highly beneficial for her to be able to walk away carrying a bunch of it in her arms—doubly true if she had to carry a baby, too.
If the female hominin were a primary driver of bipedalism, what would becoming upright mean for the evolution of our bodies?
The evidence is all around us: The food-hoarding behavior of extant chimps. The metabolic advantages of female skeletal muscle, which decline once women pass menopause.
The muscles that anchor your lower spine to your lower back, your hips, the top of your buttocks—those are slow-twitch fibers.
your jaw muscle is both the strongest muscle in your body and, no surprise, predominantly fast-twitch. You didn’t evolve to constantly chew.
The quads tend to have more fast-twitch muscle, good for explosive movement. The hamstrings, meanwhile, tend to have more slow-twitch fibers, powering more fluid movement over a much longer period.
the back side of the lower human body is better able to deal with feats of endurance than the front.
Women recover from exercise more quickly than men do.
That’s a matter not of being stronger or weaker but of metabolism and tissue repair.
Coaches can run men into the ground, in other words, but then they have to bench them. Women, meanwhile, have to hit the bench for a rest sooner, but then we can go back onto the field.
Being able to think with any amount of clarity when you’re really, really tired.
Kurdish women are allowed to join the Peshmerga. And they have. They fight, and they win. They believe ISIS fighters fear death at their hands, worried that if they’re killed by women, they won’t be allowed to enter heaven. “It’s a weapon for us,” one female Peshmerga fighter told a Western journalist. “They don’t like to be killed by us.”
What’s more, the rate of sexual assault is no higher in mixed-sex groups than in male-only ones.[*19]
In men, relaxin is produced by the prostate, but it mostly goes into semen rather than circulating in the bloodstream, and seems to help with sperm motility
The early hominins Kubrick portrays mostly ate grasses and bugs and fruits and tubers. Like other primates’ today, our ancestors’ first “tools” were probably rocks to break open nuts and sharp sticks to dig up some kind of ancient turnip.
Generally speaking, innovation is something that weaker individuals do in order to overcome their relative disadvantage.
As a primatologist in Kenya told me years ago, “Women do clever things because we have to.”
Habilis—“handy man,” or in this case “handy woman”—lived in the grassy highlands of Tanzania between 2.8 and 1.5 million years ago. This Eve of tool making was a pinch over four feet tall, with long arms and strong legs and a brain around half the size of ours.
In the places where we’ve found her fossils, we’ve also found hundreds of stone tools.
The Oldowan tools are one good reason we should think of Habilis as an Eve of tools.
Habilis was by no means the top of the food chain. Like many hominins, she was often prey.
Aside from the usual suspects—stone tools, hunting, growing really large brains—one of the big topics is how vulnerable our babies are. They’re needy not just as newborns but for an extraordinarily long time.
Therefore, in order for hominins to flourish, some kind of cultural revolution around child care must have occurred.
Species don’t really get a harder problem than the one we have to deal with: We’re really, really bad at reproducing ourselves—demonstrably worse at it than many other mammals. We’re worse than most other primates.
Most of the features that make our reproduction such a crapshoot were probably already in place by the time Habilis arrived. And they only got worse for her descendants.
The most important human invention—the very reason we’ve managed to succeed as a species—was gynecology.
In the wild, a chimp female is very unlikely to die because of pregnancy-related complications. Among wild chimps, maternal death of that sort is so infrequent that primatologists haven’t even agreed on a representative number. It’s probably quite low.
Human women, meanwhile, hover between 1 and 2 percent. If that still seems low, remember that’s the maternal death rate: the percentage of us who actually die because of pregnancy and birth within a narrow window.
The pregnancy and birth complication rate—which, again, can readily stop a genetic line in its tracks—shoots up to a full third of human women.
Fifty-eight percent of American women have continuing health problems associated with the pregnancy more than six months after giving ...
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There are two likely reasons why human reproduction is so dangerous. First, the risk of internal bleeding. Our deeply invasive placentas can rupture veins and arteries (rare), can separate from the uterine wall before it’s time (less rare), or can hemorrhage during or just after birth (still rare, but one of the leading causes of maternal death).
The second reason our reproductive system causes so much trouble is what’s called the obstetric dilemma. Compared with other apes, human women have a really small pelvic opening and human babies have a really big head.
Today’s American woman averages six and a half hours for labor. Chimps labor about forty minutes. Eves like Habilis presumably would have been somewhere between the two.
Gestation was probably getting longer, too: modern human pregnancies take about thirty-seven days more than you’d expect for an ape of our size.
There are fewer than 300,000 chimps in the entire world and fewer than a million olive baboons, even though their bodies are better suited to rapid population expansion.
These Oldowan tool users were individuals who spent a lot of time together. Flint knapping isn’t fast or easy.
It’s something you need to learn how to do.
It’s also true that in order to do something like help someone else give birth, these Eves had to become a heck of a lot less chimpy than earlier ones.
Our Eves would have needed a social structure that rewarded helpful behaviors. Mothers could help daughters, sure, but for midwifery to become widespread, collaboration between members of a wider social group would also have been key.
But to invent gynecology, our Eves needed a cooperative female society. Females needed to be able to trust
Dominant female chimps are known to kill the offspring of females with lower status. Maybe they do it out of spite or maliciousness, but from a biologist’s perspective it’s probably because it helps them maintain their social position. They don’t just kill the baby. They may even eat it in front of the crying mother.
And somewhere in the middle of all that sex, there’s one strict rule in bonobo society: nobody messes with the kids.
If a troop member harasses or harms a juvenile, they’re quickly reprimanded by nearby adults.
a bonobo give birth. She went into labor in the late morning, in a nest in a small tree, with two other females in the tree with her.
So maybe, in the evolution of human gynecology, early hominins were more like bonobos than chimps.
