Is the male variant of species an evolutionary modification of the female variant?

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Discussion by: Timman
Is the male variant of species an evolutionary modification of the female variant? 

Preamble:
[References are available on request] The Anti-Müllerian hormone, (abbrev: AMH), is a glycoprotein hormone that in humans, is encoded by the AMH gene.It is secreted by the Sertoli Cells of the testes during embryogenesis of the fetal male

And also: 
(a)    Known to inhibit the development of Müllerian ducts in the male embryo.

(b)   Prevents the development of the Müllerian ducts into the uterus and fallopian tubes.

(c)    If no AMH is produced from the gonads, the Müllerian tubes automatically develop, while the Wolffian ducts, which are responsible for male reproductive ducts, automatically die.

(d)    The gene for AMH is located on chromosome 19p13.3.
      Another gene, identified, codes for it’s receptor on chromosome 12.(e)    In men, inadequate AMH activity can lead to the Persistent Müllerian duct syndrome (PMDS) in which a rudimentary uterus is present and testes are usually undescended.The genes mentioned above are usually found to be abnormal.     

(f) AMH is also present in fish, reptiles, birds and mammals. 

Debate
:
 Do the above facts suggest that the male variant of species is an evolutionary modification of the female variant?

Additional to this: Men possess rudimentary breast tissue, including aveoli and nipples.]In common terms: Does it imply therefore that without AMH, an individual will sexually develop internal female sex organs and be devoid of male sexual characteristics?

There are examples of natural cell apoptosis in the body’s immune system which can be accepted to exist for the purpose of regulating the immune system, (through the tumour necrosis factor receptor or other similar routes), but to actually have a naturally produced protein substance in vivo to cause cell death to prevent the existence of certain structures is somewhat mind-boggling. 

I am purposefully melodramatic here to entice a debate….another example of “The magic of reality?”
 
Yours sincerely, 
Dr.Pierre van der WaltMBChB
MMed(Chem.Path)
Chemical Pathologist,Private Lab. Practice
Pretoria,South Africa. 

15 COMMENTS

  1.  I suppose you could say this as sexual development in humans in defaulted to female unless the SRY  control gene region ( sex determining region ) is activated at about 8 weeks into gestation.

    I assume parthenogenesis, fission and the like preceded sexual dichotomies by some time and all organisms were ” female, ” so to speak.

  2. I am not a medical doctor, or biologist but I find this topic very, very interesting. Topic reminded me at book of prof. Dawkins “Selfish gene”,… I am not sure, but didn’t he wrote there that a sperm originated (evolved) from eggs? I also wandered why men have tits, ha,ha,ha,ha.

  3. “Do the above facts suggest that the male variant of species is an evolutionary modification of the female variant?”

    Probably, I expect there’s more evidence for this out there too.

    The success of such an offshoot in mixing the genepool this way is obvious..

    Cloning for example as another type of reproduction has more drawbacks (see Dutch Elm Disease for example) but some plants and animals do still employ it, although random mutations may still take place to provide some variance through the inaccuracies present in those types of reproductive systems.

    To assume that females are an offshoot to the males begs the question of how did the males breed the first female? As females contain the actual bulk of the reproductive mechanism, which the males simply “activate” so to speak it seems far more likely that females were the initial breeders, though the male/female dichotomy only applies really after the males appear.

    Females breeders without a male counter part do exist (some lizards use this method), and they appear to be females that have adapted to reproduce without the males, but I’m not sure if that is a throwback to earlier times, or a later adaption from a previously male/female reproduction system in their ancestors….

    So yes, females first, so to speak, though I personallly would be cautious about there ever being a first human female as such, this stuff happened probably before mammels emerged at all…..

  4. Man did not suddenly drop from the heaven with 150 trillion cells. Man evolved from a smaller lifeform and it from a smaller lifeform until a lifeform is composed of one cell. Unicellular organism is the beginning of all living things. For it to survive, it must divide into two cells and two into four and so on. But sometimes in nature there are mistakes either internally or externally causing mutations where two cells did not completely divide. Then you may have four cells clumping together unable to complete cell division. Cells within this clump began to diverge responsibilities and functions. Some became sensors, some became propelers, and some responsible for reproduction of youngs only. Now you have the beginning of parthenogenesis where all lifeforms evolved into females. Chicken and egg dilemma is solved! Parthenogenesis ensures plentiful offsprings but genetic variation is slow. Mutations struck again and over time the male sex evolved to assist with genetic variations. Sexual reproduction ensures survival of the fittest.

  5. I’m always in favor of more comments from Dawkins but in this case I don’t think its really such a difficult question. Just look at the responses from Logicism and ZenGardener, they pretty much covered it.

  6.  The OP data is a bit above my pay grade. I can understand I’d be posing if I wrote from it.

    In a book I once read (i forget the name, it’s unfairly popular first year reading at universities) it was said the question of ‘why are there sexes?’ can be reduced to ‘why are there males?’ This asserts females as a template. This is based on the logic that many sexed species have a parthenogenic option, so males are strictly superfluous but beneficial in creating evolution strategies through sexual-selection.

    I don’t find anatomy comparisons compelling, as sexual dimorphism runs the scale from identical to fish species where the female is 50,000X larger than the male (lucky bastards). On the whole, if it can’t be said for blue-green algae, I think it’s counting angels on the head of a pin. Another matter beyond my comprehension is the evolution of the Y chromosome, but attempting to study it seemed pretty divorced from intrinsic notions of sex.

    However, there is an overwhelming trend for sexual selection to be determined by the female (peacocks, the duck vagina labyrinth, cuttle fish sperm selection, but there are a few exceptions.

    Androgen Insensitivity Syndrome
    http://www.ncbi.nlm.nih.gov/pu

    Being insensitive, yes they do develop as females, and while this might be a natural phenomenon perhaps if we could simulate the ‘opposite’ we would have genetic females that develop as males… and maybe Congenital Adrenal Hyperplasia is a tempered expression of that possibility.

    I think it’s a great question and I hope I’m wrong, because that would be terribly interesting world where the work of Valarie Solanas could be validated.

  7. Surely sexuality evolved in hermaphrodite form a very long time ago , before separating into separate single sex individuals!
    Even in the world of vertebrates such as fish, there can be sex changes in both directions within the life time of an individual.

  8. Going back even further, I don’t think single cells with horizontal genetic exchanges and simple cell divisions, can be described as male or female.  This reproduction is asexual.  

    What the OP is talking about is present day embryonic development in particular species.

  9. Wonderful post Timman. I have pulled my Biopsychology text (Pinel, J. 1990) and on p. 280, the section “Fetal Hormones and the Development of the Reproductive Organs” is found. Here it is clearly stated “Figure 10.7 represents the structure of the gonads as they appear 6 weeks after fertilization. Notice at this stage of development, each fetus, regardless of its genetic sex, has the same pair of structures, called “primordial gonads’ – primordial meaning existing at the beginning. Each primordial gonad has an internal core or medulla, which has the potential to develop into a testis, and each has an outer covering or cortex, which has the potential to develop into an ovary.”

    “Six weeks after conception, the Y chromosome of the male triggers the manufacture of a protein called H-Y antigen, and this hormone causes the medulla of each primordial gonad to grow and develop into a testis. There is no female counterpart to the H-Y antigen; the critical event in the development of ovaries is the absence of the H-Y antigen.”

    So, reading this, it is generally accepted that by default, until the presence of a Y chromosome triggers the H-Y antigen, all humans proceed to develop as females. This occurs before either set of internal reproductive ducts are fully developed (Mullerian or Wolffian), so I would say the answer to your question “(Is) the male variant of the species an evolutionary modification of the female variant” has already been answered.

  10. LizE
    Wonderful post Timman. I have pulled my Biopsychology text (Pinel, J. 1990) and on p. 280, the section “Fetal Hormones and the Development of the Reproductive Organs” is found. Here it is clearly stated “Figure 10.7 represents the structure of the gonads as they appear 6 weeks after
    fertilization. Notice at this stage of development, each fetus, regardless of its genetic sex, has the same pair of structures, called “primordial gonads’ – primordial meaning existing at the beginning. Each primordial gonad has an internal core or medulla, which has the potential to develop into a testis, and each has an outer covering or cortex, which has the potential to develop into an ovary.”

     

    There is also an interesting effect in crocodilians where sex is determined by the temperature of the nest!

    http://www.jstor.org/discover/… –
    On the Effect of Temperature-Dependent Sex Determination on Sex Ratio and Survivorship in Crocodilians
    D. E. Woodward and J. D. Murray

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