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Thanks for taking the time to actually reply @IdealForehead
Now you've said hair on the scalp is a different organ type to body hair. Ok. So why do you actually need this galea theory at all to explain the norwood pattern? If you're willing to concede that hair characteristics differ across the body why cant you accept that the reasons for balding are due to androgens and something intrinsic to the follicle itself?
Note that Androgenetic Alopecia is one of many hair loss types. DUPA, telogen effluvium, non androgenic alopecia. None of these fit into the galea theory.
Even look at androgenetic alopecia patients who bald in a diffuse manner! They dont start at the points of higher mechanical stress, all ths follicles on top fall out evenly, sometimes their hairlines are actually preserved. So even though their follices are in the galea, androgens affect them differently. How do you explain this?
Again, this theory exists only to explain the mechanism via which galeal tension leads to upregulation of androgen sensitivity genes in the Norwood pattern, which is the primary pattern of androgen sensitivity for probably at least 95%+ of men and women (once you account for scalp aromatase in women).
Differential patterns of the Norwood geography are likely best explained by this thread:
https://www.hairlosstalk.com/intera...alopecia-von-mises-2d-analysis-models.113276/
In it, you can see how with just very slightly different muscular stress patterns exerted on the galea the tension pattern changes dramatically. This can easily explain a great degree of variation in the patterns. Some patterns develop very even tension over the whole galea. It is conceivable these could be the diffuse thinners who simply thin all over until they hit NW7.
Telogen effluvium is a different type of hair loss altogether from androgenic alopecia. It is a condition where stress or other triggers cause hair cycles to become disrupted and go into premature telogen. This theory is not meant to explain that. Nor is it meant to explain auto-immune conditions or rare aberrations from the usual pattern, where there is likely some unusual extra unknown feature causing that aberration.
Scientific progress is incremental. This is not meant to provide an explanation for every single reason a person can lose their hair. Nor is it meant to be an explanation for how pubic hair develops. Saying you need an explanation for "everything all at once" or you will close your mind is not being reasonable.
As for "why" such a theory is necessary, in truth, it isn't. Many people don't have interest in knowing "why" anything happens in the body or life. There is no curiosity and there is no desire to figure out how things work. If that is your perspective, then none of this matters.
But from a developmental biology perspective, everything in the body happens for a reason. There is always a biochemical pathway that mediates differentiation of cells. If someone asks you how does a tooth develop, can you just say "by genetics" or "it just does because it does"? Well sure, genetics hold the code to making a tooth. But how does the genetic program get tweaked and modified, with parts activated and inactivated, until we go from a single celled zygote into eventually a tooth? Many cascading protein chains and environmental influences coalesce over the course of development to turn on and off genes and eventually produce that specialization.
The human body is too complex for anyone to yet explain every step of every tissue's complete development. Incrementally though, scientists explain one bit at a time. And little by little we get closer to learning the entire process that makes a human. How we make a muscle. How we make a pubic hair. How we make a head hair. How we make a Norwood zone.
In this case, we are talking specifically about the differentiation of the Norwood pattern. Just like everything else in the body, some sort of chemical signalling chain must occur in order for the Norwood zones to differentiate and develop their androgen sensitivities in that pattern. Genes don't turn themselves off and on automatically. Not directly, anyway. That's not how development works. There is always a process. This is the best explanation available based on current evidence for the process by which the Norwood pattern develops.
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