Thursday, August 9, 2018

Cellular Conflicts and Fertility: Nature Is Pro-Choice

Barbara Ehrenreich has authored a long list of books on a variety of topics.  Perhaps her best-known work is Nickel and Dimed: On (Not) Getting By in America.  She has occasionally chosen topics that involve healthcare, but the focus was not such as to allow one to suspect that her formal education resulted in a doctorate in cellular immunology from Rockefeller University.  Apparently, her range of interests were too broad to be constrained by a career in such a narrow discipline.  It would be awareness of a growing revolution in knowledge of how the human immune system actually worked that would lead her back to her original field for the production of her recent effort: Natural Causes: An Epidemic of Wellness, the Certainty of Dying, and Killing Ourselves to Live Longer.  As the title suggests, Ehrenreich is dubious about the prospects of extending life indefinitely, and she is not at all optimistic about our prospects for making significant changes in our longevity by changing our personal lifestyles. 

“The body….is not a smooth-running machine in which each part obediently performs its tasks for the benefit of the common good.  It is at best a confederation of parts—cells, tissues, even thought patterns—that may seek to advance their own agendas, whether or not they are destructive of the whole.  What, after all, is cancer, other than a cellular rebellion against the entire organism.”

“I know that in an era where both conventional medicine and the wooliest ‘alternatives’ hold out the goal of self-mastery, or at least the promise that we can prolong our lives and improve our health by carefully monitoring our lifestyles, many people will find this perspective disappointing, even defeatist.  What is the point of minutely calibrating one’s diet and time spent on the treadmill when you could be vanquished entirely by a few rogue cells within your own body?”

It was recent knowledge gained about the role of our immune systems in determining our health that prompted her to write the book.  To perform its function of protecting us from things like microbes and parasites that are foreign to our bodies, the immune system consists of an impressive array of structures and processes designed to disable or destroy these things.  However, the power to destroy can be dangerous if malfunctions can occur.  And they do.  There are at least 80 types of autoimmune diseases where the immune system, for whatever reason, turns on specific body parts.  Examples include rheumatoid arthritis, lupus, celiac disease and Graves’ disease.  Her coverage of issues related to the immune system was discussed in Cellular Conflicts: Is Extending Life Possible—or Even Worth the Trouble? 

The topic here involves another instance of cellular conflict within our bodies: the human female reproductive cycle.  It has been recognized for over twenty years that pregnancy involved a competition between the host mother and the fetus she was carrying.

“In 1993….[David] Haig put forth the surprising view that pregnancy was shaped by ‘maternal-fetal competition.’  The fetus and the placenta that attaches it to the maternal bloodstream strive to extract more nutrients from the mother, while maternal tissue fights to hold on to its nutrients—often to the detriment of the mother.  For example, the fetus may interfere with maternal insulin production, leading to elevated blood sugar levels that are injurious to the mother but deliciously nourishing to the fetus.  Or the fetus and the placenta may release chemicals that raise the mother’s blood pressure—apparently to guarantee a steady flow of nutrients to the fetus—although at some risk to the mother and ultimately to the fetus as well.”

What is less well known is that cellular conflict begins much earlier in the process.  In preparation for encountering a recently created embryo, the uterus generates a relatively thick layer of cells referred to as the endometrium.  It was thought that this layer was produced in order to provide an efficient harbor in which an embryo can dock and set up shop.  However, it seems that a woman’s uterus is very particular about which embryos it is willing to allow to attach to it.  The role of the endometrium is, counterintuitively, to make it difficult for an embryo to attach and access the mother’s blood stream.

“Today the emerging scientific consensus about menstruation hinges on the conflict within our species—a possibility that would until recently have been deeply disturbing to biologists.  In this view, the buildup of the uterine lining does not serve to entice embryos to implant, but to prevent all but the most robust and agile embryos from ever having a chance.”

To support this view, Ehrenreich references an article by the evolutionary biologist Suzanne Sadedin: Why do women have periods? What is the evolutionary benefit or purpose of having periods? Why can’t women just get pregnant without the menstrual cycle?  From it, this quote was extracted.

 “Far from offering a nurturing embrace, the endometrium is a lethal testing-ground which only the toughest embryos survive. The longer the female can delay that placenta reaching her bloodstream, the longer she has to decide if she wants to dispose of this embryo without significant cost. The embryo, in contrast, wants to implant its placenta as quickly as possible, both to obtain access to its mother's rich blood, and to increase her stake in its survival. For this reason, the endometrium got thicker and tougher – and the fetal placenta got correspondingly more aggressive.”

Sadedin included a reference to a more detailed scientific paper that provides even greater enlightenment: Natural Selection of Human Embryos: Decidualizing Endometrial Stromal Cells Serve as Sensors of Embryo Quality upon Implantation.  This paper was authored by 18 individuals with mostly unpronounceable and, certainly, untypable names.  A critical insight provided by these authors is that a significant fraction of human embryos are defective at a chromosomal level.

“Monthly fecundity rates in fertile couples average around 20%, which is disappointingly low compared to many species.  While this lack of intrinsic reproductive efficacy may reflect a multitude of complex social and biological factors, for example the loss of estrous behaviour and concealed ovulation, it is foremost attributable to the high prevalence of chromosomal abnormalities in human embryos, which limits their developmental potential and accounts for the age-dependent decline in fertility.”

Unless humans evolved some mechanism for dealing with this, a woman’s pregnancy would often be unproductive, wasteful in terms of maternal resources, and dangerous for the woman.  Consequently, endometrial cells, driven by hormonal surges produced during the menstrual cycle, undergo a transformation referred to as decidualization.  It is these decidualized cells that query the integrity of the embryo and attempt to destroy those deemed unacceptable.

“Pregnancy is widely viewed as dependent upon an intimate dialogue, mediated by locally secreted factors between a developmentally competent embryo and a receptive endometrium. Reproductive success in humans is however limited, largely because of the high prevalence of chromosomally abnormal preimplantation embryos. Moreover, the transient period of endometrial receptivity in humans uniquely coincides with differentiation of endometrial stromal cells (ESCs) into highly specialized decidual cells, which in the absence of pregnancy invariably triggers menstruation.”

“….rather than being passively invaded, these observations suggest that decidualizing ESCs actively encapsulate the early human conceptus. If so, the phenomenal response of decidual cells to a developmentally impaired embryo could represent a mechanism for controlled embryo disposal, mediated by induction of menstruation-like tissue breakdown and shedding.”

“….once the endometrium undergoes a decidual response, the integrity of the tissue becomes inextricably dependent upon continuous progesterone signalling. In the absence of pregnancy, declining progesterone levels triggers a switch in the secretory repertoire of decidual stromal cells….which activates a sequence of events leading to tissue breakdown and menstrual shedding.”

So, there you have a concise description of the process of uterine attachment by an embryo.  The endometrial layer captures and “encapsulates” as many of the defective embryos as it can and destroys them by flooding them with menstrual blood filled with cells capable of consuming the decidual layer and flushing the debris away.  Within the debris are the remnants of what were once embryos.

What we are encountering here is a process akin to contraception or abortion.  This evolutionarily developed process decides which embryos are desirable and destroys the rest.  Nature has devised a scheme by which abnormal or otherwise unwanted embryos can be forbidden to make a permanent attachment to the uterus and continue into pregnancy.  Contraception and abortion, by this rendering, are not “unnatural” processes as often claimed.  They are, in fact, perfectly natural—and critical to the health of our species.

It would seem that nature is pro-choice, and, if one wishes to believe that humans were designed by God, then God is pro-choice as well.  People who would determine during pregnancy that a fetus is damaged in some way have the technology to safely terminate that pregnancy.  In doing this, it would seem that they are assisting in the plan laid out by nature—and God.  Those who would legislate rules that require a woman to carry a damaged fetus to term are certainly following an unnatural—and un-Godly—path.

The interested reader might find the following articles informative:

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