Sexual Anatomy
arn...@my-deja.com
If H.erectus was like the other placental mammals for 150 million
years, including our closest relatives, chimps and gorillas, then the
females of that species went into heat.
Oddly, females of H.sapiens do not go into heat. There is ovulation
and a fertility cycle but the phase of intense female receptivity is
absent. Yes, women are more likely to have sex while ovulating, but the
magnitude of this tendency is the same as is found in the non-mammalian
vertebrates during ovulation. These vertebrates ( fish, amphibians,
reptiles, birds) do not have an oestrus portion in their fertility
cycle .
Oestrus (heat; estrus) is confined to placental mammals: ie-
eutherians.
But it is absent in humans.
I believe our absence of oestrus is due to a single physiological
change in the pelvic floor of our species, rather than the accumulation
of responses to hypothetical environmental or social pressures.
The importance of the loss of oestrus in this way ( as secondary to
a change in the pelvis ) means that our behaviors adjusted to our new
anatomy.
It is most likely that language, for instance, is an elaboration of
the vocalization which non-eutherian vertebrates have always used in
mating. A female eutherian without the compulsion to mate that is
oestrus, is still provided with the inherited behaviors of ancestral
species.
Absent oestrus, female choice is possible.
And female choice is the most powerful factor in Sexual Selection,
as noted by Darwin. Combine female choice with geographic isolation and
we see the diversity which makes our species unique among the placental
mammals.
Traits do not pop-up in isolation in complex species such as
vertebrates. One change of a trait will, through embryonic induction,
alter other systems in an organism.
When the oestrus "switch" was turned off, the results were complex
and extensive. Reproduction, after all, is one of the primal functions
of any living organism.
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Before you buy.
Jois Lombard
been?
Jois
Dave Timpe
"Jois Lombard" <lomb...@erols.com> wrote in message
news:39BE385F...@erols.com...
[Arne about a physiological change leading to loss of estrus]
| Arne, what do you think the single physiological change would have to have
| been?
I'm sure he'll tell you (it has something to do with genital anatomy) but
I'd guess the most likely physiological cause is functional loss of the
mammalian pheromone system and vomero-nasal organ (VNO). I recently read a
news report that they'd finally discovered a human analog to a rat's
pheromone detection gene. The only problem is that the rat has a hundred or
so, while of the 8 or so human genes, all but one were defective.
Pheromones must play a big role in signaling sexual state in species with
estrus. I think if we had a functioning system our anatomy wouldn't matter
all that much (it's more in the hormones and head than the genitalia,
anyway).
School must be back in session. All of last year's half-baked ideas are
showing up again. Maybe they'll get the oven timer set right this year. At
least the sophomores should now be "junioric", but some people seem to be
perpetual freshmen.
--
Dave Timpe
davetimpe at cybrzn dot com
Jois Lombard
ours we will have a host of new information that (maybe) will make sense. I
just saw (and nearly posted) an article comparing our genes with cows' and the
areas that are solidly conserved from mutation/evolution. Another noted
(honest!) the birds still have teeth genes, unexpressed but they are there! Who
knows?
Jois
pete
`areas that are solidly conserved from mutation/evolution. Another noted
`(honest!) the birds still have teeth genes, unexpressed but they are there!
This has been known for a long time. Disabling another gene which suppresses
the tooth gene allows them to appear. That was first done around 20
years ago, but naturally occuring faiures of the mechanism have
been recorded throughout history. Seems to me "rare as hen's teeth"
goes back a fair ways (Shakespeare? new testament? not the old, as
hens weren't in asia minor yet...)
--
==========================================================================
vin...@triumf.ca Pete Vincent
Disclaimer: all I know I learned from reading Usenet.
arn...@my-deja.com
Jois Lombard <lomb...@erols.com> wrote:
> Arne, what do you think the single physiological change would have to
have
> been?
>
> Jois
>
It is what is termed the "vestibular bulbs". In other mammals
this is a spongy piece of tissue which site almost on top of the glans
clitoridis; the end of the clitoris.
At oestrus, it swells up and raises the venous pressure in the glans.
This duplicates the action of androgens; it makes the female sexually
excited. When oestrus is over, the gland deflates and she loses all
interest in mating. This explains why the female oestrus mammal does
not have any significant change in her testosterone levels during her
cycle. Testosterone is the one-and-only substance which can cause
sexual excitement in a vertebrate.
In women, the "vestibular bulbs" are not adjacent to the glans of
the clitoris. Therefore, even though they swell during ovulation, there
is no great sexual excitement similar to heat in the other mammals.
Dr.O'Connell did the first accurate anatomy of the human clitoris
and found that the vestibular bulbs were not where the texts say they
should be. Apparently the earlier anatomists assumed that a human
clitoris was built like a non-human clitoris, and put the glands where
they supposed them to be. O'Connell proposes that the name be change
to "urethral bulbs" to reflect the true location.
(O'Connell HE; Hutson JM; Anderson CR; Plenter RJ. J Urol, 159(6):1892-
7 1998 Jun)
Arne
rwal...@my-deja.com
It sounds like there is some confusion here. The human vestibular
bulbs lie to either side of the vaginal orifice, in the region known as
the vestibule. They correspond to the bulb of the penis. Both are
composed of the corpus spongiosum. In the human male, the corpus
spongiosum continues along the ventral surface of the penis and houses
the urethra. It eventually forms the glans of the penis. The
remainder of the shaft of the penis (its dorsal surface) is formed by
the two corpora cavernosa. They also form the two crura of the penis.
Likewise, in the human clitoris, the shaft of the clitoris is composed
of the two corpora cavernosa. In the human female, the corpus
spongiosum, as noted, forms the bulbs of the vestibule and are
homologous with the bulb of the penis. There is some debate about
whether there is any corpus spongiosum contributing to the glans of the
clitoris, but the bulbs of the vetibule are certainly not, nor have
they ever been suggested by any reputable anatomist, to lie in the
glans of the clitoris.
--
Robert A. Walker, Ph.D.
Biological Anthropologist
Anatomist
Waterloo, New York
arn...@my-deja.com
>
> It sounds like there is some confusion here. The human vestibular
> bulbs lie to either side of the vaginal orifice, in the region known
as
> the vestibule. They correspond to the bulb of the penis. Both are
> composed of the corpus spongiosum. In the human male, the corpus
> spongiosum continues along the ventral surface of the penis and houses
> the urethra. It eventually forms the glans of the penis. The
> remainder of the shaft of the penis (its dorsal surface) is formed by
> the two corpora cavernosa. They also form the two crura of the penis.
> Likewise, in the human clitoris, the shaft of the clitoris is composed
> of the two corpora cavernosa. In the human female, the corpus
> spongiosum, as noted, forms the bulbs of the vestibule and are
> homologous with the bulb of the penis. There is some debate about
> whether there is any corpus spongiosum contributing to the glans of
the
> clitoris, but the bulbs of the vetibule are certainly not, nor have
> they ever been suggested by any reputable anatomist, to lie in the
> glans of the clitoris.
> --
> Robert A. Walker, Ph.D.
> Biological Anthropologist
> Anatomist
> Waterloo, New York
Hi,
Yes, you are quite correct about the location of the
vestibular bulbs.
What Dr.O'Connell contests is the term "vestibular" since they do
not lie adjacent to the human "vestibule" which is a triangular patch
of epidermal-like tissue between urethral fossa and clitoris.
In non-human eutherians, the "vestibule" is a more elaborate
structure, resembling a miniature vulva with the urethral fossa and
entrance to the vagina within it.( A good reference anatomy for the non-
human eutherian is "Miller's Anatomy of the Dog". As a veterinary
reference it references structures not only to other species but also
to humans.)
In NH eutherians the female vestibular bulbs are homologous to the
corpus spongiosum in the male penis. This relationship gives us a clue
to the morphology and evolution of this part. In marsupials the
marsupial bones are long thin bones originating at the ends of the
pelvis, in the place where the pelvic symphysis will unite the pelvis
in eutherians. These bones and their associated tissues are very
sensitive to testosterone. During mating, they join together to form a
primitive trough-like penis for the male marsupial.
In the NH eutherian the bony remnants of the marsupial bones form
the free-floating os penis. The non-ossified portion of the os penis is
actually the corpus spongiosum. In the male NH, the corpus spongiosum
is that structure which swells up after intromission (!) to lock the
penis in the vagina. Although part of the penis, it has a seperate
blood supply, a most important point.
It is my contention that a similar swelling in the NH vestibular
bulbs (homolog to corpus spongiosum) results in a rise in venous
pressure within the glans clitoridis, similar to that recorded in the
glans penis. There just are no androgen blood levels to support the
sexual excitement of oestrus in NH eutherians. I propose that the
vestibular bulbs inflate at the beginning of oestrus and deflate when
it ends, ovoiding the need for continuous (3-9 days)androgen
stimulation.
Because their location in women is different than in NH, we lack
oestrus.
Cheers
Arne