PART 1
DieHappy said:
Wow, so many high minded insults, so many semantical errors, and so much mis-information in one post!
Example?
DieHappy said:
Wow, so many high minded insults, so many semantical errors, and so much mis-information in one post!
Example?
DieHappy said:
Wow, so many high minded insults, so many semantical errors, and so much mis-information in one post!
Example?
DieHappy said:
gladiatrix said:
No, that is NOT what Teddy means. To miscarry means that a pregnancy has been established. However, most conceptions/early zygotes don't manage to establish a pregnancy and are simply washed away with the other menstruation detritus (conservative estimate is that +65% of conceptions FAIL to every result in a live birth).
Prove it.
I listed my references at the end of my post. What have you got in the way of evidence? (oh yeah, your one-liners...NOT!) But I'll make a single attempt to humor your "request" (even though it is simply an attempt to shift the burden of proof from yourself).
Here's an expert on reproduction, stem cell research and bioethics, Dr. Arthur L. Caplan:
Caplan (during an interview on Earth and Sky):
In nature, if you have embryos made by old fashioned birds-and-bees sex, in the back seat of cars, or in bedrooms, you need to understand that only 20 percent of those embryos become babies. Most are miswired. Most don't implant. Most fail. There's a huge failure rate in embryos. If you know that, then you don't really want to hold the view, I think, that most embryos are a person, because most embryos aren't. So I would try to appeal on factual grounds to a poorly understood fact that while every life begins at conception, not every conception begins a life.
There's a reason for this kind of failure rate. Ironically evidence for just why so many fail was uncovered during
in vitro fertilization (IVF). Bear in mind that doctors go to great pains to insure that the woman's body is optimally prepared to receive the zygotes generated by IVF (her temperature, uterine lining, and hormonal state are peak). However, despite their best efforts, the success rate of IVF at producing a pregnancy is only marginally better than that of getting pregnant the old-fashioned way (~25%). When one actually looks at cells from these embryos we now know why, most of them have chromosomal defects that make them non-viable.
Or as the reseachers here have observed:
As researchers seek new ways to boost the success rates of in vitro fertilization (IVF), they are finding that most fertilized human eggs appear destined for the evolutionary trash heap. A surprising number of botched chromosomes in eight-day-old embryos may explain why IVF clinics often have to try and try again to start a viable pregnancy.
British scientists recently reported a new chromosome-imaging technique that may allow clinics to improve the odds for IVF success. And their findings highlight the possible reason for all-too-common failures: Only three of 12 embryos sampled from couples undergoing IVF had the proper complement of chromosomes, according to the study by Dagan Wells and colleagues at University College Medical School, in London.
IVF workers have long suspected that some human conceptions carry a number of genetic mistakes. The new approach, which involves a genome 'check-up' prior to the implantation of the embryo, reveals just how many mistakes can occur. "I don't think people suspected the error rate would be as high as 75 percent," says Harvey Stern, director of the preimplantation genetic diagnosis program at the Genetics and IVF Institute, in Virginia.
Embryos whose chromosomes all appear healthy have an increased potential of making a baby, says Stern, who contrasts this with the "horrendously chaotic chromosome patterns" seen in some embryos. The abundant errors probably cannot be attributed to the practice of fertilizing in a dish. Although the embryos were donated by couples undergoing IVF, who may have included older women with inferior eggs, or men with problems producing sperm, the fact that three of the embryos were normal suggests to Stern that biology rather than technology is to blame.
Why is there such an "error rate" ("bad" eggs/conceptions)?
1. Upon ovulation eggs have a very short "shelf life", i.e., they start to deteriorate after 24 hours. An egg can't "wait" in the Fallopian tube indefinitely, for the right sperm to come along (so to speak). Now suppose that the egg is fertilized after 24 hours, the odds of this conception forming a viable pregnancy have just plummeted because the egg is damaged (timing of fertilization is critical).
Sperm are hearter cells, but after 72 hours, they also start to undergo the same kind of deterioration. So let's say a woman had sex 3 days before ovulation and a number of sperm have made it to the Fallopian tube where they "lay in wait' for an egg (as it were). Upon ovulation,that egg, while still prime is unlikely to be fertilized by a viable sperm.
The fertilized egg may be of poor quality, but that doesn't mean that it won't start to divide and begin it's migration to the uterus (many don't make it). It may even have the "right stuff" to accomplish an implantation and become a pregnancy, BUT, somewhere down the developmental pike, the damage catches up with the developing embryo and a spontaneous abortion occurs before the end of the 1st trimester.
2. Not all fertilizations occur when there's an endometrial lining in good enough condition to house the zygote IF it gets to the uterus. Zygotes usually don't implant in a the muscle of the uterus, they need a warm, cushy lining (nutrients, blood vessels, etc.) to house them. Again timing is everything. The blastocyst may get there too soon (no mature lining) or too late (menstruation is in progress). Either way, it passes out of the woman who never has a clue that she had conceived (a conception does NOT a pregnancy make).
3. Couple this with the fact that meiosis (
the reduction division that creates gametes--ANIMATED TUTORIAL) is prone to error (whole, duplicated chromosomes must segregate, not always done correctly). It seems that females don't have the same "checkpoint" during the process that male sperm undergo, so if there's a screw-up and the chromosomes don't segregate properly (
non-disjunction), meiosis for the egg continues (despite the genetic damage that would send most dividing cells
into programmed cell death or apoptosis). This is the most likely reason why the IVF professionals observe so much genetic carnage when they look at the embryos they create. Here are articles that addresses this issue of nondisjunction directly:
From Lack of Checkpoint Control at the Metaphase/Anaphase Transition: A Mechanism of Meiotic Nondisjunction in Mammalian Females
A checkpoint mechanism operates at the metaphase/anaphase transition to ensure that a bipolar spindle is formed and that all the chromosomes are aligned at the spindle equator before anaphase is initiated. Since mistakes in the segregation of chromosomes during meiosis have particularly disastrous consequences, it seems likely that the meiotic cell division would be characterized by a stringent metaphase/ anaphase checkpoint. To determine if the presence of an unaligned chromosome activates the checkpoint and delays anaphase onset during mammalian female meiosis, we investigated meiotic cell cycle progression in murine oocytes from XO females and control siblings. Despite the fact that the X chromosome failed to align at metaphase in a significant proportion of cells, we were unable to detect a delay in anaphase onset.
Based on studies of cell cycle kinetics, the behavior and segregation of the X chromosome, and the aberrant behavior and segregation of autosomal chromosomes in oocytes from XO females, we conclude that mammalian female meiosis lacks chromosome-mediated checkpoint control. The lack of this control mechanism provides a biological explanation for the high incidence of meiotic nondisjunction in the human female. Furthermore, since available evidence suggests that a stringent checkpoint mechanism operates during male meiosis, the lack of a comparable checkpoint in females provides a reason for the difference in the error rate between oogenesis and spermatogenesis.
This lack of discrimination in female meiosis (genetically damaged eggs not sent off into apoptosis) will occur no matter what the woman's age. What one can expect is that this kind of genetic screw-up will only increase as she ages (why the incidence of Down's syndrome increases dramatically with age).
Other primary journal articles on the above topic of female non-disjunction:
1. Meiotic and mitotic nondisjunction: lessons from preimplantation genetic diagnosis
2. Sex matters in meiosis
More References on the topic of conception loss:
3. Goldstein SR. Embryonic death in early pregnancy: a new look at the first trimester. Obstet Gynecol. 1994;84:294.
4. Jauniaux E, Gavriil P, Nicolaides KH. Ultrasonographic assessment of early pregnancy complications. In: Jurkovic D, Jauniaux E, eds. Ultrasound and Early Pregnancy. Carnforth, United Kingdom: Parthenon Publishing; 1996:53.
5. Gary Cunningham et al., Williams Obstetrics, 21st Ed. Chapter 2-Pregnancy: Overview, Organization, and Diagnosis pp 3-15 (*this text is one of the most used in the field, over 20 editions)
6. Gary Cunningham et al., Williams Obstetrics, 21st Ed. Chapter 4-The Endometrium and Decidua: Menstruation and Pregnancy pp. 65-84
7. Moore, G., Essentials of Obstetrics and Gynecology, 3rd. ed., Chapter 7-The Menstrual Cycle, Ovulation, Fertilization, Implantation and the Placenta pp 59-75
Furthermore, it is antichoicers like you and livingproofGM who assert that human BEING is present from conception. The burden of proof is on YOU (the one with the affirmative claim has the burden of proof). However, the scientific evidence (gestational development, so many conceptions "expendable") is disproof of such a claim which is why the vast majority of embryologists, ob/gyns, and biologists (myself included) don't hue to the bogus notion that a human being is present at conception (also in my references).
DieHappy said:
gladiatrix said:
IOW, just because a woman has conceived, i.e., a egg is fertilized (in the Fallopian tube), starts dividing (now a zygote), doesn't mean that she is pregnant.
That zygote still has to migrate from the Fallopian tube to the uterus and implant itself in the uterine lining (provided there is one).
The fact is that most zygotes don't manage this instead end up on a sanitary napkin/tampon or swirling down the toilet upon urination during the woman's period.
Prove it.
It? (a number of statements above...to which do you refer with the indefinite pronoun "it"?)
Fertilization in the Fallopian tube? Migration to the uterus? Definition of a pregnancy (implantation in the uterine lining of the blastocyst , i.e., stage of the zygote)?
From Kimball's Biology Pages
Pregnancy (Excerpt)
Development begins while the fertilized egg is still within the fallopian tube. Repeated mitotic divisions produces a solid ball of cells called a morula. Further mitosis and some migration of cells converts this into a hollow ball of cells called the blastocyst. Approximately one week after fertilization, the blastocyst embeds itself in the thickened wall of the uterus, a process called implantation, and pregnancy is established.
Most zygotes don't make it to the implantation stage? Consult references above (yes, you may actually have to open a real textbook or peer-reviewed journal)
DieHappy said:
gladiatrix said:
She may have conceived, but never actually gotten pregnant (that zygote failed to establish a pregnancy or the uterus wasn't ready...any number of reasons for failure).Does life really begin at conception? Is there any kind of scientific basis for that assertion?
Yes.
And your evidence is? Wow from one-liners to one-worders as an argument. I am totally underwhelmed.
continued in Part 2. . . .