The first hypothesis says that curls are caused by more number of hair cells on the negative side of the hair strand. Curly hair is believed to be better in retaining mammals warm than just straight hair without any curls. In fact, straight hairs woven with curls makes the last line of protection against temperature loss. The second hypothesis suggests that the same thing happens to human beings. They may not be able to retain temperature as well but they are warmer than straights. This means that they might adapt to cold weather in winter and not get the hang of it in summer.
Both of these hypotheses are partly true. The difference between curly hair and straight hair depends on the existence of other genetic traits and environmental conditions. There are three major categories of genes that affect the texture of your hair. These are referred to as the Caucasian, European, and Oriental genetics.
The Caucasian genes affect the basic structure and look of curly hair. It includes the Alopecia Caesaris which is the irregular shape of hair shaft and the classification of Alopecia Totalis that includes total or partial loss of curly hair. This is usually caused by an excess of the protein keratin in the scalp and body. This protein is known to help the follicles in making and maintaining a regular shape and size.
In addition, this genetic type can also be influenced by the presence of two additionalalleles. These are the typed 2 and the non Typed 2 genotypes. The non Typed 2 genotype is referred to as incomplete dominance. This means that it is possible for a person to have one copy of the gene but lack the other one. It can still be advantageous in terms of appearance though. A person with one copy of the non Typed 2 genotype is still able to produce natural-looking curls even if the other one is missing.
The Caucasians that have the Caucasian genotype for curly hair all belong to the European ethnic group. They are known to have lighter skin compared to other people, as well as pale hair that turns darker when it’s exposed. These people have two other major phenotypes that affect the texture and curl pattern of their curly hair. These are known as the Ashkenazi and Jewish ancestry. The Ashkenazi is characterized by lighter skin tone along with dark hair and the Jews are characterized by their dark hair and light skin.
The European race or group has two major genotypes which are recognized as the Iberian and the Basque. These two ethnic groups have different physical features including the European hair texture. These consist of twoalleles that have an uneven distribution in humans. There are two alleles that are synonymous with curly hair i.e. the wavy hair and the hardy-weinberg equilibrium.
Both of these racial groups have variations in the distribution of their twoalleles. For example, the Ashkenazi has a high concentration of the wavy hair trait while the Basque has a high concentration of the hardy-weinberg equilibrium. These ethnicities have differences in the concentration of the hair follicles in the scalp as well as the structure of the hair strands. This is because of the genetic differences between the two races that determine the characteristics of curly hair.
One major difference between curly and straight hair is that, in case of the Basque, the distribution of the wavy hair trait is more in the upper part of the scalp while the straight hair follicles are more frequent in the posterior part of the scalp. In case of the Iberian peninsula, both types have more straight hair than curly but, they have more distribution of the straight hair than the curly one. The Iberian Peninsula has more distribution of the straight hair than the other ethnicities. Thus, the distribution of the hair follicles, structure of the hair strands and their characteristics are different for all three ethnicities and this results in differences in the type of curl patterns.
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