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this female advantage is present in a number of other mammalian species, too,
A typical teenage male will grow a nose about 10 percent bigger than a typical girl his size.
estrogens enhancing OSN performance and the androgens somehow suppressing or interfering with their smelling abilities.
In 2014, one lab
Though the sample size was relatively small—only so many cadaver brains to go around—the results were clear: women’s olfactory bulbs have massively more neurons and glial cells than men’s do, even controlling for size.
More than 50 percent more. Women’s are simply more dense. And given the way olfactory bulbs process signals, density might have a large effect on overall function. The density, and thereby strength, of any given signal is enhanced. The ripples spread faster over the pond. And given that women have the same number of odor receptors as men do, the primary site for how women’s olfactory system differs from men’s might be here in the bulbs. Given how primitive olfactory bulbs are, this difference may be present from birth.
For example, pregnant women sometimes suffer from pica: the uncontrollable urge to eat things like dirt or hair or pencil shavings. The placenta sucks a lot of iron out of a pregnant woman’s body, and women who have pica also tend to have iron deficiencies.
pregnant woman’s
Some of the nausea is simply a result of basic indigestion: a pregnant woman’s hormones also tend to slow down her intestines, making her feel bloated and generally nauseated.
Cyanide famously tastes and smells of bitter almonds—in fact, almonds would still be dangerous today if ancient farmers hadn’t managed to breed the cyanide out of them.
Because their bodies do so much of the heavy lifting when it comes to reproduction, the death of a female is always going to be far costlier for the species’ local fitness than the death of a male.
the size of the visual processing portions of the brain increased dramatically.
The defining circumstance is hunting at night, when it’s that much harder to see things, so being able to utilize a parallax is important. In this line of thinking, maybe primates’ eyes slowly moved forward because it’s hard to catch insects in the treetops at night.
Most paleontologists assume that our early mammalian Eves were largely nocturnal insectivores, skittering about in the safety of moon shadow.
Most mammals are color-blind—unable to differentiate between red and green.
This is how color vision works: special receptors on our retinas, called opsins, respond to different wavelengths of light; longer waves skew red, while shorter waves are bluish. The retina takes these different color wavelengths and “mixes” them in the underlying nervous system. One receptor activates for blue, and another for red, and the brain sees purple—so long as you have those two different receptors.
The genes responsible for our red-green color vision arose by gene duplication roughly forty million years ago, right around the time a bunch of proto-monkeys floated on a land raft across the Atlantic Ocean and created a new monkey kingdom on the North American continent.
The genes for creating that opsin, as luck would have it, are located on the X chromosome.
The groups with a mixture of color vision among their members appear to be slightly better at foraging as a group.
Attention directs perception just as perception influences attention: the sensory array and its corresponding brain centers are in near-constant communication with one another and signals go both ways.
Generally speaking, human eyes do two things: saccades and fixations. Saccades are the twitchy ways eyes move from one spot to another in a visual field, and when they linger on a spot, it’s called a fixation.
And as the artist learns that the forehead usually takes up a full third of a human face below the hairline and begins to internalize ways of “correcting” his or her brain’s normal interpretations of the visual field, the face on the canvas starts to look more human.
Because women are generally born with two X chromosomes, some are actually tetrachromats—they see the world not in three color dimensions but in four.
Like birds, these women can tell far subtler differences between red, green, and yellow wavelengths, potentially making them able to see as many as 100 million distinct colors: a full 99 million more than the average human being.
women who have the genetic predisposition to see all those extra colors usually don’t. That’s because the color receptors aren’t what fundamentally decide what colors we perceive. There’s a directional stream of information between the eyes, the optic nerve, and the vision regions of the brain.
As many as 12 percent of all human girls may be born tetrachromats.
But because they grow up in environments that will never ask them to use it, they’ll never know that they have this ability. It simply won’t develop.
The strange extra cones in their retinas will lie dormant, or maybe their optic nerve just ignores them.
The very first fruiting tree was probably some sort of gingko (Zhou and Zheng, 2003).
Still, if you know only 900 characters, you’ll be able to read about 90 percent of a Chinese newspaper.
Adult men tend to have fifteen times more circulating testosterone than women of reproductive age.
The big reason pig farms castrate male pigs is that otherwise, once they reach puberty, their testicles pump out androstenone, which becomes concentrated in their adipose tissue and can make the meat taste like sweat and piss. It’s called boar taint.
We’d have done the same for oak trees, but their toxins are more complex than almonds’, so acorns are best left to squirrels.
Because retinal cones are more diffuse toward the edges of your retinas, your peripheral vision is largely red-green color-blind for smaller objects (Hansen et al., 2009).
from tests of human tetrachromats, it seems the fourth type of human retinal cone is sensitive to wavelengths in the middle space between red and green. The fourth bird cone is specially dedicated to UV wavelengths.
ETHIOPIA, 4.4 MILLION YEARS AGO
Many scientists think we actually started that process in the trees: walking on our hind limbs along larger branches as we used our hands to pluck fruits and bugs on tiny, higher boughs, especially when the trees were shorter and hanging was better supported than sitting on branches. It was easy to take that behavior and apply it to walking upright on the ground.
By 4.4 million years ago, we were doing it regularly. That’s when Ardipithecus ramidus walked the earth—the Eve of human bipedalism—about 3–4 million years after the last common ancestor of chimps and humans.
Standing about three feet eleven, Ardi was somewhere between a chimpanzee and a really furry human, which is to say, she walked upright but still spent a lot of time in the trees.
Walking for Ardi was probably a bit like walking in a snowshoe—she hadn’t yet evolved the ability to roll smoothly from heel to toe.
Modern humans inherited the problems that come with any sort of bad design. Our feet are, in many ways, the biological equivalent of duct-taping your car’s bumper back on when you don’t have the money to send it to the body shop.
Combine that with a female body that tends to “sway” in motion (wider hips, funky knees, more butt fat), and eventually something’s gotta give. It’s probably going to be the big toe joint—both the most flexible part of the foot and the one that receives the most pressure.
Unlike men’s, women’s femurs come into the knee joint at an angle.
Because our hips are wider than men’s, our knees are somewhat closer together to help balance that differing center of gravity.
That sexual dimorphism lines the pockets of orthopedic surgeons, who regularly perform significantly more knee...
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Consider that every pound of body weight normally puts an extra pound and a half of pressure on the knee join...
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Despite their heavier weight, their masculine body traits—straighter knee joints, more leg muscle, and lower levels of relaxin, all of which make men’s knees and backs less prone to injury than women’s—make drag queens less likely to suffer long-term damage from their high-heel habits.
Relaxin will also never mess with the ligaments tying together a drag queen’s foot bones—something every pregnant woman has to deal with.
But our lumbar spine—the tiny tailbone, the fused sacrum, and the rest of the vertebrae that rise to our waist—absorbs more of that distributed force than our mid- and upper spine does.
Somewhere in puberty, men’s and women’s average body plans diverge, with men’s shoulders and chests broadening and bulking up, while women’s hips widen and their breasts develop.
