Why Does Baldness Exist? Ctd

A reader advises:

Please urge your female reader who wrote you complaining of her hair loss to get her thyroid checked.  Thyroid disease is a common cause of hair loss in women.  I lost about half of my hair when I got sick several years ago, and all I can say is, it is a good thing I had so much hair to begin with.  I think most of us experience hair loss with age, but 26 is far too young to be having such problems.

Another has a "warning to those men who are reading the posts exclaiming the positive impact of hair transplants":

Like your reader who had a follicular transplant, one of my good friends also had this procedure when he was in his mid-20s; receiving rows and rows of transplanted hairs placed in neatly symmetrical patterns over the entire top of his head.  In the short run, this procedure, I'm sure, did much to help the self-esteem of a young man prematurely balding and panicked about his looks and the impact on his attractiveness to prospective mates.  

The problem is that someone experiencing balding that severely in his early/mid-20s, is likely going to continue to bald.  Now, in his early 40s, my friend has the top of his obviously implanted head cut extremely short – making the unnatural pattern even more noticeable – because the balding has extended down creating a bare ring of head before the fringe of hair at his ear level.  The worst part of all of this: because of the horrible scarring created by the removal of the strip of hair from the back of his head to create the transplants, fully shaving  his head is no longer a reasonable option.  It's an unfortunate example of having to live with a constant reminder of the vanity of youth.  He would have been better to just have left his hairline to nature.

Another provides a science lesson:

In the study of classical genetics, male pattern baldness is often used as the textbook example for what is termed an "X-linked" chromosomal trait. These are traits that demonstrate an instantly recognizable inheritance pattern in a family tree. Because it's the sperm's contribution that determines your gender, if you are male you definitely got your X-chromosome from your mother, and your Y-chromosome from your father.

A woman with two X-chromosomes might have 1 chromosome that produces malfunctioning hair follicle genes, and another that is fully functional. If the functional proteins mask the effect of the dysfunctional ones (which they do for baldness), she would carry the dysfunctional gene without ever showing its effects.

Thus, there wouldn't be much pressure from sexual selection to reduce the amount of male pattern baldnessbecause that gene is carried by a mother who never shows any signs of the trait. She passes the gene on in equal probability to both sons and daughters, so even if bald men were to never reproduce, the gene would still be passed on from one generation to the next.

From looking at an image of the human sex chromosomes, it's not hard to imagine how much information lives on the X-chromosome that is missing from the Y! Mom is hard at work, determining if you have hair, or hemophilia, or are color blind, or a number of other issues, whereas dad never lifts a finger.