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Why do humans have eyebrows?

Why do humans have eyebrows?


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Why do humans have eyebrows? It seems that it isn't necessary but only humans have them, correct? So what is the use of them for humans? I hear that they protect our eyes. However, isn't that what eyelashes do? What other functions do eyelashes have?


Eyebrows function to protect the eyes from perspiration and provide shade.

Eyelids function to protect the eyes from foreign objects and sunlight.

Eyelashes function to protect the eyes from foreign objects, produce sebum (a lubriant that the eyelids) and acts as protection for the eyes from tears [1].

The above seems to be backed up by health how stuff works and the anatomy of the eye from emedicinehealth.

However, note that biologist dont have any concrete reasons for the eyebrow. This is just what many of them agree on I suppose. Here is another resource from sciencefocus.


How to Tell a Girl You Like Her

Let me bring you back to high school: You’re an awkward teenage boy, and you see your high school sweetheart staring you in the face. You don’t know how to ask her out, so what’s the best way to nonverbally tell her you dig her? Should you:

  1. smile at her
  2. wink at her
  3. show her your muscles
  4. flap around like a chicken

Trick question—there is no right answer! By the time you’ve decided to signal your interest, she’s likely ALREADY sent you dozens—if not hundreds—of tiny micro signals that indicate if she’s interested in YOU. Signals that might have gone right over your head if you don’t know what to look for.

Most early signaling is done by women. Women are truly the “selectors” who attract attention by displaying subtle nonverbal signals 1 . So if you know what to look for, there’d be no need for your awkward high school self to muster up the courage to face rejection in the first place.

Knowing how to spot the telltale signs of attraction will help you be ahead of 99% of men out there.

So what should you look for? Here’s what to look for to successfully read a female’s body language.


Why Do Men Have Nipples?

Every day, people have their tonsils, appendix, and wisdom teeth removed&mdashand after the pain subsides, they proceed without a hitch.

The truth is, it&rsquos not all that apparent why many parts of your body are there, or what they actually do.

&ldquoEvolution moves toward features that are advantageous over others, so at some point all anatomical features were important to our early ancestors,&rdquo says Anthony Weinhaus, Ph.D., director of the University of Minnesota&rsquos Human Anatomy program.

Some of these still serve a purpose&mdashjust not necessarily a function crucial to our survival anymore. Here are real explanations for these seven seemingly pointless body parts.

Let&rsquos get the biggest news out of the way: All men start off as women.

&ldquoAll embryos begin female, and if it masculinizes, it becomes male but keeps much of the same anatomy,&rdquo says Weinhaus.

Nipples are the same in men and women, but without an influx of hormones like estrogen, they&rsquore simply chest ornaments on men.

2. Armpit Hair

There&rsquos no definitive story for underarm hair, but its location offers a clue.

There are two types of sweat glands in your body: eccrine and apocrine, the latter of which are mostly in your armpits, explains Daniel Lieberman, Ph.D., professor of human evolutionary biology at Harvard University.

You use apocrine for sexual signaling. Presumably, the hair holds on to the secreted odors so they&rsquoll stay around long enough for a potential mate to catch a whiff, he explains.

The evolutionary purpose of eyebrows is debatable: In one camp, scientists believe brows keep sweat and rain off your eyes, which would help in primitive hunting and navigation.

Lieberman favors the hypothesis that eyebrows serve to communicate your emotions, but they may also communicate your identity.

Behavioral neuroscientists from Massachusetts Institute of Technology found that people were less likely to recognize pictures of celebrities without their eyebrows than without their eyes.

The researchers speculate that eyebrows have remained because they&rsquore crucial to identifying faces and navigating social circumstances.

The appendix is a vestigial organ, which means it has lost most of its ancestral function.

&ldquoOne idea is the human appendix is remnant of what used to be a larger fermenting chamber in our gut,&rdquo Lieberman says.

Since humans stopped eating uncooked or low-quality foods like grass, this chamber is no longer useful.

Recent research, though, suggests the appendix might be an essential hangout spot for healthy bacteria.

&ldquoYour microbiome is very important to digestive tract function, so this reservoir would allow microbes to recolonize your gut after inflammation or digestive issues,&rdquo he explains.

Tonsils are technically lymph nodes&mdashpart of the lymphatic system, which is vital to your immunity.

&ldquoYour oral cavity is an entryway to your body, so immune cells in your throat can help you fight respiratory infections,&rdquo Lieberman explains.

Sometimes your tonsils get inflamed and infected, which is when they&rsquore removed.

Your lymph nodes are incredibly important, but there&rsquos some redundancy, so if a pair is taken away, you can survive without them, Lieberman adds.

6. Wisdom Teeth

Like monkeys, men have three permanent sets of molars.

Until recently, wisdom teeth were never an issue for humans: &ldquoTeeth don&rsquot change size. They&rsquore grown before you use them, and then they erupt to the surface,&rdquo says Lieberman.

Jaws are bone and, like the rest of your body, need to be supported and used in order to grow properly. Since humans now eat soft, cooked foods as children, our jaws don&rsquot grow to the full capacity.

This leaves inadequate space for all your molars, so your wisdom teeth grow in crooked and need to be pulled.

Male foreskin takes years to separate from the glans (head), which is unusual enough of a process to suggest one if its main functions may help prevent infection, especially in infants.

It helps shield the opening of the urethra from any contaminates or bacteria, explains Weinhaus.

It also protects your reproductive chances: Without a foreskin, the glans rubs against objects, like your clothes, and develops a thick layer of skin to desensitize itself, Weinhaus says.

Foreskin keeps men more sexually sensitive, which would&rsquove encouraged our ancestors to reproduce more.


How hair, eyelashes and eyebrows grow

If I had to sum up some of the most frequently asked questions on TIA, they are mostly about eyebrow and eyelash growth and they run along the lines of:

Will over-plucked eyebrows ever grow back?

Why did my eyelashes start falling out when I started to use a growth product?

Will I have to use these growth products for the rest of my life/What will happen when I stop?

How long before I see results?

There isn't a short answer to any of these and I am afraid that they require at least some understanding of how hair growth works: yep, it's time for hair growth 101.

The hair growth cycle

All hair &mdash whether on the head and brows, the eyelashes or the unmentionables &mdash grows in phases. There are three of them, to be precise. The only thing that differs (from, say, lash to head hair) is how long the phases take. But we'll come back to that.

Anagen &mdash the growth phase

Each follicle can grow many hairs over a lifetime: on average, each grows a new hair around twenty times. The phasing of the growth cycle is staggered amongst the follicles. Which prevents us from periodic phases of baldness when the growth cycle stops.

The growth phase is called anagen. How long anagen lasts is determined genetically, and varies between the sexes and from one person to another. It is the length of this time that determines how long the hair will grow. For head hair, the anagen phase can last from three to as much as seven years.

Fun fact/myth buster: It is not true that cutting your hair makes it grow faster or thicker. Nor does shaving your legs make the hair grow coarser. The length of the growth phase and the width of the hair shaft are the results of your genes, and are not affected by anything you do to your skin or to the hair shaft itself.

Catagen &mdash the intermediate phase

The anagen phase is followed by a short resting phase. This catagen phase lasts between two and four weeks. No pigment is made during that time, and the follicle stops producing hair. The base of the follicle moves upwards towards the surface of the skin.

Telogen &mdash the shedding phase

The telogen phase lasts for three or four months. During this time a new hair begins to grow from the hair follicle. As it grows upwards the old hair will be shed naturally or may be pulled out. Tweezing is easily and painlessly done with telogen hairs. These are the hairs that come out when you shampoo or brush your hair.

Shedding is part of the normal process of the replacement of old hair with new. At any one time, around one in ten of the follicles on an individual's head are in the shedding phase.

The new hair emerges from the same opening at the surface of the skin as the old one, and the hair cycle begins again.

As people age, the hair cycle can become shorter (this isn't true for everyone and depends on your genes). The follicles gradually give up producing long, strong hair, and the hairs become thinner and shorter. This can happen to lashes, brows, leg and arm fuzz and so on.

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What's different about lashes and brows?

Not much. Eyelashes shed just like head hair. It may be that people who think their new eyelash growth product is causing their lashes to shed are nothing more than the victims of coincidence. On the other hand, it could seem to be a more dramatic loss than normal. This could be due to the fact that some eyelash growth products, specifically the ones that contain prostaglandins, speed up the growth cycle prompting a bout of shedding.

The growth cycle of eyebrows and eyelashes are a mere blink of the eye compared to head hair. Eyebrows take up to 64 (give or take) days to come back fully. Eyelashes are even more fleeting, taking only four to six weeks to come and go.

Follicles &mdash the growth engine

Each individual hair is formed inside a hair bulb deep in a hair follicle. The follicle is a tiny but powerful factory. Although some male balding is due to testosterone, there is a growing understanding of the role the follicle plays in other kinds of hair loss (female hair thinning, sparse lashes and brows). A healthy follicle apparently produces nice strong hair.

If you pull a hair out of a follicle another one will grow up in its place. Not so, say some of you: "I over-plucked by eyebrows during the 80s when I didn't know better and now they won't grow back."

I'm not sure if the over-plucking theory is no more than urban myth, but I couldn't find any hard evidence to support it. What I did find, over and over again, were unsubstantiated statements along the lines that over-plucking causes follicle damage. How? Look at the diagram: the follicle is snuggled below the epidermis and the root is way down. Unless the tweezer is used as a probe, I don't get it.

Furthermore, more scientific references I have come across say that there isn't much environmental damage that can be done to a follicle that would stop it producing hair. There would have to be severe physical damage such as burning or scarring to achieve that.

Some (tentative) answers to the FAQs

Over-plucked eyebrows should, theoretically, grow back if the follicles are given some TLC (which is what products such as Truth Vitality Brow Vitality Complex ($39 in the shop), with copper peptides and emu oil, are supposed to do). I regularly (approximately every other day) apply Brow Vitality Complex and my once-moth eaten brows are nicely filled in and the hairs are darker and thicker.

You do have to resign yourself to continued use of these products if you want to continue to have results. When you stop using an eyelash growth product, your growth cycle will revert back to normal. Plus, you may (depending on your age) need to counteract the post-42 thing.

As far as results go, this will vary from each person because of the genes that gave them their follicles and dictated the length of their growth cycles. And if you are lucky enough to start using a product during the telogen cycle, you might see results more quickly because you were just about to go into a growth period anyway.

Watch Marta's video in which she explores the reasons behind hair loss and offers solutions for stimulating the growth of healthy hair at any age:

Read more about Truth In Aging's Truth Vitality hair care collection:


Why Do We Have Eyebrows? Finally We Have an Evolutionary Explanation

Eyebrows. What’s the point? Science has an answer at last.

Highly mobile eyebrows that can be used to express a wide range of subtle emotions may have played a crucial role in human survival, new research from the University of York suggests.

Like the antlers on a stag, a pronounced brow ridge was a permanent signal of dominance and aggression in our early ancestors, which modern humans traded in for a smooth forehead with more visible, hairy eyebrows capable of a greater range of movement.

Mobile eyebrows gave us the communication skills to establish large, social networks in particular to express more nuanced emotions such as recognition and sympathy, allowing for greater understanding and cooperation between people.

The study contributes to a long-running academic debate about why other hominins, including our immediate ancestors, had gigantic brow ridges while anatomically modern humans evolved flatter foreheads.

Senior author of the paper, Paul O’Higgins, Professor of Anatomy at the University of York, said: “Looking at other animals can offer interesting clues as to what the function of a prominent brow ridge may have been. In mandrills, dominant males have brightly coloured swellings on either side of their muzzles to display their status. The growth of these lumps is triggered by hormonal factors and the bones underlying them are pitted with microscopic craters – a feature that can also be seen in the brow bones of archaic hominins.”

“Sexually dimorphic display and social signalling is a convincing explanation for the jutting brows of our ancestors. Their conversion to a more vertical brow in modern humans allowed for the display of friendlier emotions which helped form social bonds between individuals”.

Using 3D engineering software, the researchers looked at the iconic brow ridge of a fossilised skull, known as Kabwe 1, held in the collections of the National History Museum.

It belonged to a species of archaic hominin – Homo heidelbergensis, who lived between 600,000 and 200,000 years ago.

The researchers discounted two theories commonly put forward to explain protruding brow ridges: that they were needed to fill the space where the flat brain cases and eye sockets of archaic hominins met, and that the ridge acted to stabilise their skulls from the force of chewing.

Professor O’Higgins said: “We used modelling software to shave back Kabwe’s huge brow ridge and found that the heavy brow offered no spatial advantage as it could be greatly reduced without causing a problem. Then we simulated the forces of biting on different teeth and found that very little strain was placed on the brow ridge. When we took the ridge away there was no effect on the rest of the face when biting.

“Since the shape of the brow ridge is not driven by spatial and mechanical requirements alone, and other explanations for brow ridges such as keeping sweat or hair out of eyes have already been discounted, we suggest a plausible contributing explanation can be found in social communication.”

According to the researchers, our communicative foreheads started off as a side-effect of our faces getting gradually smaller over the past 100,000 years. This process has become particularly rapid in last 20,000 years and more recently, as we switched from being hunter gatherers to agriculturalists – a lifestyle that meant less variety in both diet and physical effort.

Co-author of the paper, Dr Penny Spikins from the Department of Archaeology at the University of York, said: “Modern humans are the last surviving hominin. While our sister species the Neanderthals were dying out, we were rapidly colonising the globe and surviving in extreme environments. This had a lot to do with our ability to create large social networks – we know, for example, that prehistoric modern humans avoided inbreeding and went to stay with friends in distant locations during hard times.

“Eyebrow movements allow us to express complex emotions as well as perceive the emotions of others. A rapid “eyebrow flash” is a cross-cultural sign of recognition and openness to social interaction and pulling our eyebrows up at the middle is an expression of sympathy. Tiny movements of the eyebrows are also a key component to identifying trustworthiness and deception. On the flip side it has been shown that people who have had botox which limits eyebrow movement are less able to empathise and identify with the emotions of others.

“Eyebrows are the missing part of the puzzle of how modern humans managed to get on so much better with each other than other now-extinct hominins.”

Source: Eurekalert/University of York
Image: Paul O’Higgins, University of York


Answer

We put this question to Des Tobin, Professor of Cell Biology, University of Bradford.

Hair growth is very susceptible to hormones, to the so-called sex steroid hormones: principally oestrogens and androgens. The dominant hormone for males is in the androgen category, particularly testosterone.

Surprisingly, the levels of testosterone continue to increase with age up until the age of 70. Since most male hair is responsive to androgens, with age and with increasing hormone levels you tend to get more and more vigorous hair growth, particularly in the areas that were perhaps not as robust as when the individual was younger. For example, on the nose, ears and on their eyebrows.

The nose and the ears have got thousands and thousands of hairs. They're so small you can't see them. In fact, the tip of the nose is the hairiest part of the body in terms of density of hairs per unit area.

With time, these tiny - formerly invisible - hairs can be stimulated with these male hormones, which go up with age, and can therefore become more cosmetically visible with age. The same applies for the eyebrows and for the ears.

In women, oestrogen levels drop after menopause, and their lower levels of testosterone become more engaged with the process of hair growth because they stimulate whereas oestrogens tend to inhibit.

So you're just releasing more stimulatory power from the androgens we have.


Types of hand gestures

Hand gestures, just like side dishes in a meal, come in many varieties. According to researcher David McNeill&rsquos classification of hand gestures, there are 4 kinds&mdashiconic, metaphoric, deictic, and beat.

Iconic Gestures

Iconic gestures are visual images of what we&rsquore talking about. For example, if you were talking about how great it is to walk on grass bare feet, you might form your index and middle finger into &ldquolegs&rdquo and walk them through the air.

Iconic gestures don&rsquot have any meaning on their own. A spinning finger might mean someone pirouetting or a tornado the meaning will depend on the context.

Metaphoric Gestures

Metaphoric gestures are visual metaphors. These gestures come up when we have to talk about abstract ideas, such as philosophy or math. When people are asked to describe algebra problems (&ldquohow many hours would it take for x workers to complete a construction&rdquo type question), they gesture using long sweeping motions to show &ldquochange&rdquo or small taps or zig zags for other elements of the problem.

The four types of hand gesture. (Photo Credit : Shutterstock)

Deictic Gestures

Deictic gestures are pointing gestures. They indicate a direction of something, somewhere or someone.

Beat Gestures

Lastly, beat gestures consist of tapping to the beat of your speech. Every time you stress a word, your hand might move downwards to enhance the effect of what you&rsquore saying.


A History of Eyebrows: See How They Transformed Over the Years

Eyebrows are a hotter topic than ever in 2014. Not a day goes by that we don’t hear about so-and-so’s amazing brows, or marvel at things like eyebrow extensions and even lace-front brow wigs, but brows have more history—and more to do with history—than you’d ever suspect. Follow us through a comprehensive history of brows, from ancient civilizations until today.

Ancient Egypt: As depicted on the bust of Queen Nefertiti, Ancient Egyptian women sported arched brows darkened with powders made from minerals. Greek historian Herodotus documented that when a cat died in a home, everyone who lived there would shave their eyebrows in mourning. When a dog died, everyone in the house would shave their whole body as well as their head.

Ancient Greece and Rome: The ancient Greek people valued purity, so women often left their brows untouched or darkened slightly with black powder. In both cultures, unibrows were prized as beautiful, desirable features worn by the most intelligent and lusted-after women. If one didn’t have a unibrow, they would create one with black paint.

The Middle Ages: The forehead was the most important feature of the medieval period, which is why women often removed their eyelashes and eyebrows. Later in the 15th century, Queen Elizabeth’s reddish blonde (these days we’d call it strawberry blonde) inspired many women in her country to dye their hair and brows in similar reddish shades.

Victorian Era: Women who wore obvious makeup were frowned upon in this era and thought of as prostitutes, which is why ladies of breeding left their brows quite bushy and untamed.

1920-1930: As seen on silent movie starlets like Clara Bow, women wore their eyebrows extremely thin and straight by way of extensive plucking, lending to a dramatic, pensive look. They also used petroleum jelly or Vaseline to groom and add shine and emphasis to slender brows. The 󈧘s were the first era in which regular women began to cull inspiration from celebrities and entertainers, which has continued into today.

1930-1940: Women continued to wear dark, shiny and severely tweezed brows, but rather than sport straight lines, they favored dramatic high, rounded arches, which sometimes extended all the way to the temple. Jean Harlow‘s thin, curved brow defined the era.

1940-1950: A softer, more natural look came into popularity in the 󈧬s, with movie stars like Lauren Bacall bringing heavier, prominently arched brows into vogue as regular women followed suit. The Old Hollywood red carpet looks we see today are heavily inspired by the thick, well-groomed brows and cherry red lips of this era.

1950-1960: Think Audrey Hepburn, Marilyn Monroe, and Elizabeth Taylor—the celebrities of this time sported thick, dark brows that were often penciled in to achieve a bolder, more enhanced look. They retained similar arched shapes to the brows of the 󈧬s, but the effect was stronger and more pronounced as the defining feature of the face.

1960-1970: Sophia Loren had the most storied brows of the decade, and for good reason: She shaved them off entirely, then would painstakingly pencil them back in using super-short, precise strokes. Audrey Hepburn‘s straight, natural brows remained popular, while art scene “It” girl Edie Sedgwick blackened hers to contrast her platinum hair for a serious statement look.

1970-1980: A handful of brow looks were favored during this time, including thicker, more natural brows as worn by the hippies of the decade and the thinner, more pronounced arches worn by disco enthusiasts. Actresses like Lauren Hutton popularized natural, “fresh-faced” beauty looks, and eyebrow trends followed suit, with many women setting aside their tweezers.

1980-1990: Bushy brows were the ticket to 󈨔s glamour, with Brooke Shields as the cover girl du jour. Thick, ungroomed “caterpillar” brows were all the rage, and a heavy, almost disheveled look was desirable and emulated with the help of brow pencils and powders.

1990-2000: Anyone who came of age in the 󈨞s will remember it well: Super-thin, over-tweezed brows ran rampant this decade, with stars like Drew Barrymore and Pamela Anderson rocking teeny-tiny arches that often resulted in a perpetually shocked-looking expression. The 󈨞s were not a good decade for eyebrows.

2000-Present: The early aughties held onto the past decade’s thin brows, but we’ve since gone the opposite way of over-plucking, instead favoring thick, lush looks and natural arches. Cara Delevingne‘s beloved brows dominate the catwalk, with everyone from celebrities to regular people using pencils, waxes, powders, gels, and more to emulate the bold, dark, statement brow effect. We’re also seeing a lot of bleaching, both on and off the runway, for a bizarre, otherworldly look.


Are Smooth Brains Bad?

Yes. Dear god yes smooth brains are bad.

You’ve probably heard of our cuddly friends the koala. While they’re critically endangered thanks to recent climate change events, koalas are also incredibly dumb.

Like even the food they eat is terrible for them. That’s why koalas are almost always sleeping. Eucalyptus leaves (basically their sole diet) are poisonous for most other animals–luckily the koalas are an exception. Unluckily, eucalyptus is not nutritious at all, and also is really hard to digest. Plus, while koalas are relatively resistant to eucalyptus poison, they’re far from immune. So it’s possible for koalas to poison themselves with their own diet if they go too far.

As for being hard to digest, so much energy is devoted to breaking down the leaves, so koalas have to sleep to make it all up.

It gets worse, because koalas are so dumb they only recognize eucalyptus leaves on a branch. If you plucked some leaves and put them on a plate for a koala, it wouldn’t recognize the food as food. Which means you could theoretically starve a koala to death in a room full of the only thing it eats.

Koala teeth also aren’t made to eat eucalyptus. Some herbivores get around grinding their teeth by having them grow nonstop, or what have you. Koalas don’t have that, so once their teeth grind down (often before they die of old age), they just… Give up and starve to death. That’s got nothing to do with smooth brains we just thought it was incredibly pathetic from an evolutionary standpoint.

These bears also fall out of trees a lot (this is because they’re dumb) so sometimes they’ll just die falling out of a tree.

Basically, koalas have really smooth brains and that’s why they’re so stupid.

Koalas and Climate Change

Stupid as koalas are, it would be a shame to lose them to rampant climate change (no seriously Australia is on fire). If you’d like to donate to our friendly bear-fiends, here’s a link.

Think you know your brain anatomy? Test your neurological knowledge here.