Answer behind hair variations in Europeans distinctively
So I feel this deserved its on thread for what I found that may explain why there is hair variations that can determine why it may be curly (some what of a primary focus), wavy and straight hair in both Asians/Europeans.
This is a copy/paste from my another answer from another thread that I thought deserved its own so here it is:
If you want updated findings of the impact of neanderthals/Denisovans on the Eurasian/Pacific populations that is tied in with some humor on the slideshow to keep your attention. Also, it shows additional findings recent that ties in with it that is present by Svante Pääbo giving a lecture at Berkley that is approximately an hour long: https://www.youtube.com/watch?v=8flcCtIkTUc
Fun fact: Tibetans inherited a gene from Denisovans possibly that helped them require less oxygen intake at the altitudes that they live in.
Overall from what I could gather from neanderthal studies is that Eurasian populations inherited genes that encoded for one's keratin to have straight hair follicles overall. Nonetheless, when the divergence between Asian and European populations occurred Asian inherited some neanderthal genes that predisposed them with a higher density ratio of the hair follicles (that are quite straight in its own right) possibly from other hominins in general. As the article conveys in the study by Medland et al. (2009):
Quote:
The EDAR gene that controls hair thickness shows one of the most convincing signatures of positive selection in the East Asian genome. 4
Whereas Europeans within the three-cohort (generational differences) study based in Australia, they found the phenotypic variation in Caucasoids is more common in Northern Europeans in general by the TCHH gene:
Quote:
The T allele at rs11803731 is the derived state and shows a striking geographic specificity to Europe and western-central Asia, reaching its highest frequency in Northern Europeans ( Figure 1E), suggesting that the variant arose somewhere in this broad region. The modern frequency and distribution of de novo mutations will generally be determined by random genetic drift and migration. However, because rs11803731 influences a highly visible phenotype, it is an intuitively obvious target for natural or sexual selection. 13 [...]
Alternatively, rs11803731 may be associated with structural variation. TCHH is a single-stranded α-helical protein with two or three highly repetitive regions, depending on the species (Figure S8). In sheep, the reference protein (CAA79165.1) is 1549 amino acids long, but variation in the number of complete and partial repeats in the C-terminal repeat region is seen across different strains.25 and 26 In the human TCHH protein, repeat lengths range from approximately 6 to 30 amino acids, corresponding to 18 to 90 bp of DNA sequence. A number of SNPs and insertion or deletion polymorphisms are present, particularly in the first and third repeat regions (dbSNP; see Web Resources), and this gene might harbor allelic length variants, as seen in sheep and in another highly repetitive gene in the human chromosome 1p21 region, involucrin (IVL), where alleles differ across human populations in the number of both short tandem repeats and single base changes within repeated sequence. 27 and 28 Such length variation has not been reported for TCHH, and it remains to be determined experimentally whether such variation is common, affects the structure or length of the protein, and/or is tagged by SNPs flanking the repeated regions.[...]
In conclusion, we report a quantitative trait locus that affects hair form in Europeans. The association accounts for ∼6% of the variance in hair morphology in this group and falls within the Trichohyalin gene, which has a known role in hair formation. The patterns of allele frequencies are striking, with the highest frequency of these variants observed in Northern Europeans (Figure 1), paralleling the observation of the straight-hair EDAR variant in Asian populations ( Figure S9).
Here is the percentage of this phenotypic variance of hair follicles in Europeans as well as a possible explanation for curly hair:
Quote:
Hair morphology is one of the more conspicuous features of human variation and is particularly diverse among people of European ancestry, for which around 45% of individuals have straight hair, 40% have wavy hair, and 15% have curly hair.1 [...] The degree of curliness is correlated with the distribution of hair keratins and cell type within the hair fiber, with the number of mesocortical cells decreasing as the curl intensifies.
As of right now the reason behind curly hair is unknown as of right now for the time being:
Quote:
However, the genetic variants influencing hair curliness in Europeans (which has been shown to be highly heritable 5) are unknown.
Nonetheless as the study says they are yet to experiment with this further since the reason behind curly hair is unknown as of right now with multifactorial (interaction between environment and genes) traits:
Quote:
So that we could take full advantage of the information available in the ordinal scale, the data were analyzed via a multifactorial threshold model that describes discrete traits as reflecting an underlying normal distribution of liability (or predisposition). Liability (predisposition) [sic], which represents the sum of all the multifactorial effects, is assumed to reflect the combined additive effects of a large number of genes and environmental factors, each of small effect, and is characterized by phenotypic discontinuities that occur when the liability (predisposition) reaches a given threshold.10 [...]
The association was found in all three samples, suggesting that the effect is robust to the age differences between the samples and that the liability (predisposition) threshold model accounted for the differences in the phenotypic definition across the samples.
http://www.sciencedirect.com/science...02929709004649
Essentially what this is saying is that each population has a distinctive allele (variation in genes) that plays a role in one's inheritance that can result in variations in one's genotype (genetic makeup of an individual that determines one's distinct physical appearance) that goes can be affected during prenatal development (environment) of an offspring. Hence, it is largely multifactorial that it differentiates its self from polygenic (interaction between two or more genes) inheritance such as eye color.
