When we first learned basic reproductive science, giggling behind our hands in school, we learned that a vast number of tadpole-like sperm swim up to a round, floating egg somewhere in the mysterious geography of the female reproductive tract. Voila! An embryo is made, which (blah, blah, blah) becomes a person in roughly 40 weeks (give or take).
While this is not untrue, it is a remarkable simplification of processes that we can barely wrap our minds around. Consider that when the sperm and egg meet, they carry with them half of the genetic information for an entire human being. According to the National Institutes of Health Human Genome Project, human DNA contains about 20,000 genes on 23 pairs of chromosomes — half from each parent. All starting with that ridiculous-looking sperm and egg.
In terms of just the physical length, every human cell has about five feet of DNA (if you could pull it out, stretch it and measure it). How much information is encoded is still being studied, but scientists are studying ways to use DNA to store information since it is much more compact than computers as we know them, and its ability to store data is only just being understood.
So that’s what the sperm and egg bring to the table. Then, when their individual strands unite, we don’t just get a copy, a clone — we get an entirely new creature. Very much as a married couple become “one flesh,” their progeny do so in not only a spiritual but a magnificently beautiful chemical way. From that comes the remarkable development of a human being.
But what is the progression of that development? We hear a lot of talk that seems to minimize the development of a human life in the womb. But it could be that it is so overwhelmingly magnificent — but so common, in our experience — that we fail to see what it looks like, what really happens. I’m not an obstetrician or an embryologist, but here’s a quick summary:
In the first month, mother and baby form the amniotic sac (in which the baby will develop) and the placenta (which will nourish it). There is also formation of early cardiac cells, a heartbeat begins (not yet detectable by routine exam), and face and eyes begin to form. This small human is a few millimeters in length. (Take a second and get a ruler. You can come back.)
Next, the second month sees the early development of the beginnings of limbs (called “limb buds”). In addition, there is early formation of the neurological system, including the brain, further growth of the heart and even some bone development from cartilage. All within eight weeks of that sperm and egg delivering the instructions for assembly.
Soon after, the third month sees the full formation of all limbs, and all organ systems, with the baby beginning to move its extremities and mouth. There are beginnings of teeth, finger-nails and toenails. Blood is pumping through the circulatory system, and the urinary system is working as well. Imagine that. From two small cells, in three months a tiny human has formed. This amazing creature has all of the information in each cell that is necessary for it to go on to birth and live for decades — and it had all of it from the very beginning.
There’s more of the same in the fourth month as organs develop further, including reproductive structures. Facial features are more defined, including eyelashes and eyelids, and the neurological system becomes more active.
By the fifth month, fetal movement is increasing. We use the word “quickening” to describe onset of fetal movement that the mom can feel. Hair develops on the baby’s head, and a fine hair covering some other areas forms as well. This is called “lanugo.” There’s also a protective covering on the skin called “vernix caseousa” that is shed after birth.
This small, mostly complete human is by now about 10 inches long and between eight and 16 ounces in weight.
From here on out, most of what happens is further development, as the interaction of the mother’s body and the baby’s unique genetic instructions continue to develop him or her in preparation for birth and life.
At six months, eyes (one of the most complex structures in living things) begin to open, movement continues, and the baby responds to external stimuli like loud noises. Babies born at around 23 weeks can survive with aggressive medical care.
Month seven sees development of a layer of fat, decreased amniotic fluid (since the baby is getting bigger and needs room), more refined hearing, and even visual responses to light. The baby may be 14 inches long and weigh two to four pounds.
Moving forward, month eight is marked by further increased neurological development and growth in size and activity. However, the baby’s lungs are not yet fully developed. He or she has more fat as well. The baby may be 18 inches long and up to five pounds.
During the ninth and final month, he or she has increased neurological reflexes. The baby will begin to descend into position for birth, and, with increased size and decreased space, may be less active than before. It may be seven pounds or more, as many mothers will tell you.
If you take some time to read about any part of human development, or any part of human physiology, it’s evident that this process is beyond complex. It is not “simple biology,” nor can it be reduced to random clumps of cells — when, in fact, the precision and predictability of it is breathtaking. It is also more beautifully precise and well-orchestrated than the greatest work of art or music, as incredible as the stars in the sky.
The next time you contemplate your own existence, or the existence of every person you will ever know, meet or pass on the street, remember that their body, their existence, was the product of this process. Then praise God.
Some helpful online resources:
https://americanpregnancy.org/healthy-pregnancy/week-by-week/baby-development-month-by-month/
https://my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth