Today, I want to share some thoughts, actually a chain of thoughts about how very few hormonal changes may effect various aspects of the phenotype.
One of the most visible phenotypical differences between East- and West Eurasians are the eyes (epicanthic fold of many East Eurasians) and the nose ('Bigger' nose of West Eurasians compared to East Eurasians). The latter one is the topic of my post.
So what makes the nose grow big? Besides embryonic development, most guys with a big nose know the answer: puberty.
Puberty is characterized by a hormonal change maturing a child body to an adult body. For men, this means change of the voice, beard growth, body hair, and nose growth. All these mayor phenotypical changes are mainly caused by one molecule,
Testosterone (and its derivative Dihydrotestosterone or short DHT) .
Testosterone and DHT are hormones produced in the testes (in the Leydig cells), so both are messengers, transmitted as a little molecule from one part of the body (testis) to another part of the body (e.g. nose, hair follicle, etc.) via the blood vessels (to be precise, the skin can produce DHT by converting Testosterone to DHT). To receive and 'read' this transmitted molecular information, these tissues express a specific receptor called Androgen receptor. The timing, time duration and the strength of the information (testosterone concentration in blood) as well as the sensitivity/number of the Androgen receptors contributes to final outcome of the phenotype.
For example, baldness is associated with a mutation in the Androgen receptor causing hypersensitivity, which makes body hair darker and longer, and hair on the scalp progressively thinner after adolescence. The Androgen receptor is located on the X-chromosome, so this baldness-causing mutation is inherited from the mother (recently, mutations on other chromosomes has been associated with baldness, too). More severe mutations in the gene of the Androgen receptor can cause a loss of function (Complete androgen insensitivity syndrome or CAIS). Male individuals with such a non-functional Androgen receptor have a female appearance and different from both men and women, they mostly lack secondary terminal hair (e.g. underarm hair).
To get an better idea where the Androgen receptor is present and most likely crucial for phenotypical outcome, I can recommend this website: http://biogps.org/#goto=genereport&id=367
Higher expression (and most likely more presence) of the Androgen receptor can be found in various tissues, most of them are important for sexual differentiation of men and women: skin,
Deltoid muscle, heart atrium, Skeletal muscles, in the epithelium of the
Fallopian tube,
Adipose tissue, breast (Breast ductal cells, breast lobular cells,
mammary glands, nipple cross section), Penis, Prostate glands, Vulva, Vagina,
Urethra, Cervix, Ovary, etc.
So, do men with more body hair have a more prominent nose? Viewed from a global perspective, I would say yes but I don't have any data for that.
Does the sexual dimorphism differ between the ethnic groups? Viewed from a global perspective, I would say yes but I don't have any data for that, either. I believe that sexual dimorphism is more pronounced in West Eurasians than in East Eurasians.
I believe that men with a more prominent nose are perceived as more dominant, similar to men with more facial hair. You might heard of the term 'Aristocratic nose', which is basically describing a bigger nose. And maybe big-nosed men are more dominant because Testosterone and the Androgen receptor are also present in the brain tissue where both together play an important role in behavioral outcome (e.g. aggression).
So, maybe there is a correlation between hormonal regulation, behavior, and 'nose' phenotype.
So where did the 'prominent nose people' first emerge? Evolutionary speaking, it is believed that narrow noses are an adaption to colder climate, and bigger noses are an adaption to warmer climate, so the first people with a more prominent nose must have been living in a warmer climate. Interestingly, ethnic groups speaking Indo-European and Semitic languages tend to have more people with prominent noses.
