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Q: sperm evolution and response to birth control ( No Answer,   6 Comments )
Subject: sperm evolution and response to birth control
Category: Science > Biology
Asked by: nonprofitstuff-ga
List Price: $3.50
Posted: 22 Aug 2006 10:13 PDT
Expires: 21 Sep 2006 10:13 PDT
Question ID: 758426
I'm seeking some information that I read in an article a couple of
years ago. Please provide hyperlinks and/or summary of scholarly
literature that discusses an increased male human spermatoza response
to female human use of birth control. I recall the article that I read
said something about sperm becoming stickier to the uterus thus
decreasing the effectiveness of birth control by use of "the pill".
There is no answer at this time.

Subject: Re: sperm evolution and response to birth control
From: dops-ga on 22 Aug 2006 11:19 PDT
Sound like a scientifically flawed article! The premise makes no sense
The primary mechanism by which BCPs prevent pregnancy is by preventing
ovulation. The sperm can hang-out all month long and there will still
be no conception without ovulation. Many pills have the side-effect of
causing an increase in the mucus outside of the cervix, which could
presumably slow sperm entry into the uterus, but this is only an issue
if there is ovulation.

I've read article before about sperm evolution under sexual
selection/competition (very interesting), which suggest that humans
did not evolve under monogamous conditions. Never have I heard any
indication that BCPs are a selective force in sperm evolution.  The
only thing that I could imagine is that in some women, BCPs can cause
a change in the vaginal and uterine environment (chemistry, pH, etc.),
perhap this could be a driving force for compensatory changes in sperm
motility or viability, but again this would not circumvent the
effectiveness of the BCPs because they act to prevent ovulation.
Subject: Re: sperm evolution and response to birth control
From: aj999-ga on 22 Aug 2006 11:47 PDT
Also, there has only been about one, maybe two human generations since
the Pill was invented.  It would take many, many generations for
evolution to happen.
Subject: Re: sperm evolution and response to birth control
From: nonprofitstuff-ga on 22 Aug 2006 13:23 PDT
Your comment is very interesting. Perhaps the article that I read was
flawed. However, if the pill prevents ovulation as you remark in your
comment, why do women still have a period whereby releasing blood
among other liquids once a month?
Subject: Re: sperm evolution and response to birth control
From: dops-ga on 22 Aug 2006 13:57 PDT
Ovulation is not required for menses. Most BCPs contain estrogens and
progesterone. Amongst other processes estrogens act to cause an
increase in the thickness of the endometrium (the lining of the
uterus). Normally estrogens increase slowly through the menstrual
cycle and culminate right around ovulation. With use of BCPs one has a
high level of estrogens at the beginning of the cycle. The high levels
of estrogen early inhibit the production of follicle stimulating
hormone (FSH), so that no egg is matured (and no ovulation occurs).
There has already been however, an increase in the endometrium, this
is not dependent upon FSH. When estrogen levels decrease toward the
end of the menstrual cycle (or when one stops taking the BCP for the 7
days off) this triggers shedding of the endometrium. So in human
females mentrual bleeding is independent of ovulation or a fertile

I don't think this is true of animals that undergo estrous. In these
animals the "bleeding" is an indication of ovulation and receptivity.
Subject: Re: sperm evolution and response to birth control
From: keystroke-ga on 22 Aug 2006 15:41 PDT
I would also like to add that the human sperm would somehow need to
know that a female was using the pill to prevent pregancy in order to
pass this information on to the testes to tell them how to change in
order to bypass this.

As far as the sperm, testes and male are aware....ejaculation is as
good as a pregnancy, whether the female is on the pill or not.

Subject: Re: sperm evolution and response to birth control
From: dops-ga on 23 Aug 2006 09:12 PDT
Hi Keystroke,

This isn't really a problem. If one were discussing a form of birth
control that inhibits sperm's ability to access the egg, for example
spermicidal gels, then one could conceive of a situation in which the
widespread use of spermicidal gel was causing selection for resistent
sperm. For example by chance a sperm cell carries a mutation that
causes it to be resistent to compound X (the active agent in the
spermicidal gel). This resistent sperm cell is able (against all odds)
to fertilize an egg. Since sperm are haploid, there is 100% chance
that this gene will be passed onto the next generation. Assuming the
birth of a son, 1/2 of the son's sperm cells will have this new trait
(resistence to compound X).  Compared to the rest of the population
this male will have higher fertility, since there is the chance to
reproduce with or without the use of the spermicide. He will then pass
on this allele to his offspring and so on... Even assuming that the
initial resistent sperm cell resulted in the birth of a daughter, 1/2
of her sons would produce sperm cells that segregatged 1:1 for
resistence to compound X. In cases where selection is acting directly
on the gametes, changes in the frequency of benefial alleles can occur
very quickly (that is not the frequency with which they arise- this is
just a reflection of mutational rate) in a population.

Having said all this. There is some evidence that "knowing" is
involved in sperm production. Apparently when a man is with a woman
that he suspects of infidelity or when he has been away from partner
for an extended period of time, he apparently makes more of a specific
type of sperm cells, whose pupose is to attack foreign sperm. I don't
know what the mechanism is for this. I suspect it may have something
to do with emotional stress causing changes in hormone levels, but it
is nonetheless intriguing.

There is also this odd situaltion in bats where female infidelity has
resulted in the selection of males with large testes (larger testes
more sperm production). Apparently the production of testes comes at
the expense of brain formation (both are expensive to produce).
Compared to the a related species in which female fidelity is greater,
males who mate with promiscuous females have smaller brains and larger

You have to wonder who funds these experiments.

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