11 Wild Facts About Human Bodies

Alfred Blaschko, the German dermatologist, named the stripes on humans. In 1901, he spotted line patterns on his patients' skin.V-shaped lines extend over the spine. U-shaped lines appear on the chest and upper arms. S-shaped lines run across the torso. Perpendicular lines go up and down the arms and legs, and spirals appear on the head.V-shaped lines extend over the spine. U-shaped lines are on the chest and upper arms, and S-shaped lines run across the torso. Additional perpendicular lines go up and down arms and legs, with spirals on the head.

These are now called Blaschko's lines.Blaschko's lines.These lines are usually not visible to the human eye. Ultraviolet light shows them; they appear clearer in some skin conditions, mostly skin problems.

People with an inner monologue might find it surprising that not everyone has one. If you lack one, you might not even realize an inner voice exists.you might not even realize an inner voice exists.An inner voice exists.

Psychologist Russell Hurlburt admits studying the voices in people's heads—or the lack of them—presents a challenge. His research found thathis research found thatMost people believe they think in words. Many people are wrong.Visualizing one's self in a situation happens more often for many humans. They think in images instead of words.Visualizing one's self in a situation happens more often for many humans. They think in images instead of words.

Writing things down helps people without an inner voice. Some people claim very little thought exists. Still, many people think inmultiple ways and have several inner voices.they go simultaneously.

Hurlburt found his subjects talked to themselves only about 25% of the time.about 25% of the time.Research into how that inner talk happens revealed more findings. A 2015 studya 2015 studyconcluded that "internal interlocutors" fell into four groups: faithful friend, ambivalent parent, proud rival, and helpless child. A subsequent 2019 studya subsequent 2019 studyindicated that inner dialogues come from "self-reflection, self-observation, cognition, and... accompanying activities."

School taught that the human body has 206 bones. Most of the time, this is true, except for rare extra bones. One possible outlier has always been a person with a fabella—a second kneecap.

About 100 years ago,less than 10% of humans had a fabella, but 2019 research shows that percentage has more than tripled.more than tripled.In 2018, 39% of people were thought to have fabellae.

This small sesamoid bone grows in the knee tendons. It may happen more often in humans because knee joints face more pressure. As humans weigh more, the body might form extra bones to strengthen the knee. But,as researchers point out,"it could be doing nothing at all."

A human pregnancy lasts 38 to 40 weeks, or roughly 10 months.roughly 10 months.If a woman's toenail falls off the same day she gets pregnant, she waits for it to grow back when her child is born.

Not everyone'stoenailsgrow atthe same rate,regrowing one can takeas many as 18 monthsThe toenail takes longer to grow back than a small pinky toe nail does to grow.

Toenails are keratin, the same material as hair and fingernails. They are also the same material as animal hooves, horns, and claws. Humans possess both toenails and fingernails.Toenails and fingernails.It takes two or three times longer for toenails to grow than fingernails. Scientists do not fully know why, but they think it relates to different uses and blood flow.The uses for and blood flow to the hands and feet.The hands and feet.

As far back as the 1970s, there were studies.as the 1970s., there were.Studies.Studies indicated the human body had more bacterial cells than human cells. Ruth Ley, a microbial ecologist from the Max Planck Institute, stated that while bacteria on and in humans are "essential to your health," the data showed a different reality.UC San Diego's Rob Knight spoke.Researchers in the 2010s tried to measure the difference between human and bacterial cells.

The highest estimates showed a 10:1 ratio of bacterial to human cells. Scientists like Ron Sender, Shai Fuchs, and Rob Milo now suggest a 1:1 ratio instead.Scientists likeRon Sender, Shai Fuchs, and Rob Milo offereda 1:1 ratio.These revised numbers let researchersquote "a better estimate" without ignoring the human-bacteria link.researchers (and anyone wanting a surprising fact at a dinner party).

Being lactose intolerant might seem limited to a few people, but about two-thirds of adults actually struggle to digest milk sugars, specifically lactose.Two-thirds of adults have this issue.actually have problems digesting milk sugars (lactose).

Babies drink milk when born, either from their mothers or another mammal. They digest it because their intestines have high levels of lactase enzyme. As humans age, the lactase in the body drops, making milk harder to digest.

This means one-third of the world's population has broken the old rule. Many people can drink milk, eat cheese, and enjoy dairy without issues. This means the small group that tolerates milk has increased over thousands of years.

Scholars like this.Mark Thomas at University College London and Loren Cordain from Colorado State University say humans tolerate more lactose because they endure potential side effects from milk's nutritional value and the rise of good refrigeration.milk's nutritional value, and they developed better refrigeration.

If you run your tongue along the roof of your mouth, you may not feel much. People with a torus palatinus have a very different experience.torus palatinus.However, the experience is very different for those with a torus palatinus.

Most human mouth roofs are smooth with only a slight ridge. A torus palatinus creates a noticeable ridge that changes size a lot. This condition is more common in women and Asian people, affecting up to a quarter of the world's population.

Torus mandibularis, a condition causing bony growth on the bottom of the mouth, exists alongside torus palatinus, which is more common in males. Both conditions are harmless.Genetics likely cause these issues.Bruxism might also cause them, but the film-holding tabs push against the bony growths, making dental X-rays uncomfortable.

Humans breathe through mouths or noses, depending on many factors. Breathing through the nose gives humans filtration via cilia, temperature control, and moisture balance.Cilia in the nose filter air.Nose hairs moderate temperature and balance moisture.

Having two nostrils makes it seem like humans breathe through both at once. In reality, humans switch between nostrils, with the majority of air passing through one nostril and only a small amount through the other.Most air goes through one nostril.Only a minimal amount of air passes through the other nostril.This cycling happens throughout the day. This explains why single-nostril breathing feels much worse with a stuffy nose.Single-nostril breathing is much worse with a stuffy nose.This process helps optimize nasal efficiency.Nasal cycling also helps humans smell correctly.For decades, people widely believed all human embryos start as females.This belief stemmed from research showing the male (Y) chromosome does not activate until five or six weeks into embryonic development.

Researchers challenged claims that an embryo needs the Y chromosome to become male in 2014.Opposing a passive view of sex differentiation, researchers found some mammals' chromosomes need activation to develop female traits.In 2017, scholars found proteins that actively eliminate male genetic material, complicating the view of embryo development.This means sex determination and sex differentiation in humans are separate processes.One 2020 study found that until the sixth week of embryonic life, no sexual difference is observable in the fetus.Sex determination results from the chromosome makeup at conception, involving more than just X and Y material.Human beings have about 5 million hair follicles.

This number is roughly the same as chimpanzees. However, human hair shows less and less coarse texture than primate hair.2014Terminal hair covers eyebrows and heads. Vellus hair covers everything else.In 2017Archaeologists and genetic researchers suggest a climate change millions of years ago caused the shift.eliminated male genetic material.male genetic material.

What does this mean? Humans are not all "female by default." Sex determination andsex differentiationTwo parts make up human sex differentiation. One study shows this.from 2020The study determined that no sexual difference appears in the fetus until the sixth week of embryonic life.Sex determinationSex determination also comes from chromosome makeup at conception. This involves more than just X and Y genetic material.

Human beings have about5 million hair follicles. This matches chimpanzees. Human hair shows less and is less coarse than primate hair.

Chimps and other primates have what we call "fur." Humans haveterminal and vellus hair. Terminal hair forms eyebrows and head hair. Vellus hair covers everything else.

Hairiness similarities between humans and chimps point to shared ancestry. Differences show how our paths split.

Researchers suggest archaeologists and geneticists propose a climate change caused the differences.a change in climatemillions of years ago caused the shift.This means..., bipedal hominids needed to sweat after they began hunting and foraging in the sun; chimps stayed cool in the shade. Bipeds shed hair for running and sexual selection.

Throughout history, humans have tried to understand the organ in their heads—something that needed a name. This depended onThis is who you asked.in antiquity, people thought the brain wasThe brain is hollow., it held the soul or served as the center for thinking. From the Middle Ages through the 16th and 17th centuries, people explored theThe brain's anatomy is complex.this helped improve knowledge of its function.

Ancient Greeks called the brain ""phren," a word that meant the same as "mind" or "thought." The Latin word for brain is cerebrum; scientists still use it inneuroscience. As these languages affected others, words for the brain were made, used, and applied by humans and their brains as needed.