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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". |
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There is no answer at this time. |
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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 period. 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. --Keystroke-ga |
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 testes. You have to wonder who funds these experiments. |
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