"Teacher, I really didn't perm my hair!" - A desperate cry from a natural curly girl

——Why are some people naturally curly and some not?

——How is the self-curling curl formed?

——And, can Xiao Juanzi become Naoko?

Why is he a self-made

But I have a wig, oh no, straight hair?

Hair is mainly composed of a type of protein called keratin (keratin is also the main substance that makes up the stratum corneum of our skin and nails). The keratin in hair is rich in cysteine ​​residues, and the sulfhydryl groups in them can be oxidized to form disulfide bonds. When the two sulfur atoms forming the disulfide bond are very far apart, a force that causes distortion is generated.

Schematic diagram of disulfide bonds in proteins. | Wikimedia Commons

The more disulfide bonds there are that are far apart, the greater the curliness of the hair. The same principle is also used in hair perms. After destroying the original disulfide bonds in the hair, chemical ointments can be used to create new disulfide bonds in artificially curled hair, making the hair curly.

In addition to the distribution of disulfide bonds, the shape of hair follicles also affects how hair looks. Hair follicles are small cavities where hair grows. Their size determines the thickness of hair, while the shape of hair follicles affects the shape of hair: if the hair follicle is round, the hair growing out of it is usually straight, while for people with curly hair, the shape of the hair follicles is often oval or even asymmetrically curved.

Hair that grows from oval follicles or hook-shaped follicles is curly.

How natural is curly hair? Whether it is natural or not is mainly determined by genetics. Among Europeans, most people have naturally curly hair (40% have wavy hair, 15% have ringlets), while 45% of Europeans have straight hair. The probability of inheriting curly hair from parents is as high as 90%. In East Asia, most people have thick straight hair.

In 2009, researchers from the Queensland Institute of Medical Research in Australia published a paper in the American Journal of Human Genetics, finding that the gene TCHH encoding trichohyalin may affect the curliness of hair in people of European descent. As for East Asians' straight hair, it is related to a gene called EDAR. This gene encodes the Ectodysplasin A receptor, and its specific variant is believed to be closely related to East Asians' thicker straight hair, more sweat glands, and smaller breasts.

While it's unclear exactly how these different hair types evolved, one theory is that as early humans with curly hair expanded from Africa to areas with cooler temperatures and less sunlight, straight hair became more effective at protecting against the cold than curly hair, which is more adapted to strong ultraviolet rays. Some experimenters claim that curly hair is better at protecting against UV rays, while straight hair is better at retaining warmth - straight hair tends to reduce air loss close to the scalp, providing a layer of insulation for a part of the body that would otherwise easily lose heat.

What's the use of knowing this? It's really useful. If people understand the laws of hair shape, they can develop new ways to make hair curlier or straighter.

Not only that, it can also predict the likelihood of a baby having straight or curly hair. Of course, the coolest thing is that people may be able to extract effective information from DNA samples at the crime scene to determine whether the suspect's hair is straight or curly.

So, little test takers, your spring is probably coming soon.

Author: Nezha

Editor: Calo

Reference Information

[1]https://www.ncbi.nlm.nih.gov/pubmed/28370528

[2]http://www.sciencedirect.com/science/article/pii/S0002929709004649

[3]http://www.wisegeek.org/what-makes-curly-hair-curly.htm

[4]http://www.telegraph.co.uk/news/science/science-news/6751910/Curly-hair-gene-discovered-by-scientists.html

[5]https://en.wikipedia.org/wiki/Trichohyalin