Yesterday, I responded to a blog post on “Why Men Can Speak on Abortion.” with: “This article is simply a rehashing of age-old arguments about why males should control women and their bodies. The fetus is part of a woman’s body until it’s born.” I received a couple of stinging replies, which suggested to me that those respondents didn’t understand much about human biology.


So I thought I’d offer an overview of what happens after fertilization in the normal course of embryonic and fetal development, in order to put the biological dimension of the abortion issue into perspective. It also seemed like it might work as a blog on this site as well. This version is more detailed than that response and I may have to split it into two segments. Again. Sorry for the wordiness!

Human Embryonic Development

The production of a new human being is a long, slow process, fraught with danger for both the developing embryo/fetus and for the mother who carries it. Until the advent of contemporary medicine, many women died during pregnancy or in childbirth – approximately one woman for every six births. The death toll among embryos and fetuses was, and still is, even higher, between 30% and 50%. Most are spontaneously aborted because they are not viable for a variety of reasons, including genetic abnormalities, improper implantation, developmental mishaps, hormonal imbalances in either mother or fetus, and environmental toxins to which the woman has been exposed. These natural accidents cause things to go awry; it’s truly amazing that anyone is born normal.

Things start out with a fertilized ovum. The ovum is produced in the woman’s body, and the fertilizing sperm is thrust into it from outside. The union of an ovum and a sperm is called a zygote; the term conceptus is also used for the product of the union of ovum and sperm and the very earliest period of development.

The ovum provides all nutrients necessary for the first week of development, and it contains the mitochondria that will produce energy for development; thus, the developing organism’s mitochondria will carry only the maternal genes. So Mom’s huge cell is carrying the load here; it offers nutritional molecules and energy production. The itty bitty sperm simply provides some DNA. A great many new cells are produced by cell division following fertilization, until the resulting conceptus is a microscopic ball of cells that looks rather like a Volvox.

After several days to a week, the ball of cells implants in the uterus, and begins to burrow in, developing membranes that are designed to suck nutrients from the mother’s blood supply like a parasite. After the placental membranes have been established, only then does the embryo, itself, begin to develop. During those first two weeks of development, the vast majority of the cells produced will become embryonic membranes. (Would the placenta be considered a human being? Should we keep it alive after birth? Should we develop vast warehouses to nourish old placentas because they were once part of a conceptus. Should we bury them and give them gravestones?)

The Embryonic Stage

As an embryo begins to develop, it takes on a variety of shapes, undergoing a metamorphosis from a worm-like creature, to a fish-like creature with gills, to a quasi-human creature with a tail, holes in its heart, and webbed hands and feet. Indeed, the embryo passes through several stages that reflect the evolutionary history of mammals. The embryo will remain attached to the mother’s uterine lining during the remainder of development. It will absorb nutrients from the mother’s blood and will slough some of its own cells into the mother’s blood stream.


Some of the sloughed embryonic cells can lodge in organs throughout the mother’s body, and they may continue to live and even divide outside the womb. These parasitic remnants may give the mother trouble in years to come in the form of “autoimmune” diseases, from which women suffer at a much higher rate than men.

The early months of pregnancy are usually difficult for the mother, who often suffers from nausea and vomiting, enormous fatigue, and general malaise. Her body must accommodate to a foreign body growing rapidly inside her like a tumor, diverting her blood supply to its purposes and absorbing a large share of the nutrients she digests.

(to be continued…)