The modern abortion debate among Bible-believing Christians and others involves the question of when life begins. Perpetuating the debate is the fact that the Bible itself does not explicitly state a precise moment when human life begins. That omission has led theologians, religious scholars, and laymen across all political spectrums to put forth a variety of interpretations and opinions about when life begins.
Some say that life begins at conception, citing Psalm 139:13–16 as evidence, where the Psalmist speaks of being formed in the womb by God. Others argue that life begins at birth, when a newborn takes its first breath, pointing to the creation account in Genesis 2:7 where God breathed the breath of life into Adam. Still others maintain that life begins at some unspecified point between conception and birth, referencing Exodus 21:22–25, in which accidental injury to a pregnant woman that endangers the life of her fetus is addressed. These and other life-defining passages in Scripture have resulted in conflicting opinions among Bible believers on exactly when human life begins.
From a scientific viewpoint, there is also diversity of opinion among researchers. In general, however, life is defined by biologists using criteria that distinguish living organisms from non-living matter. While specifics may vary by context, the following are commonly used criteria to determine if an organism is alive:
- Cellular Organization: Living organisms are composed of one or more cells, which are the basic structural and functional units of life. Cells carry out various metabolic processes necessary for life.
- Metabolism: Living organisms exhibit metabolism, defined as chemical reactions that occur within cells to maintain life. These reactions typically involve the conversion of nutrients into energy and the synthesis of molecules needed for growth and repair.
- Homeostasis: Living organisms maintain internal stability and balance through homeostasis, which involves regulating factors such as temperature, pH, and nutrient levels within a defined range.
- Response to Stimuli: Living organisms respond to stimuli from their environment—such as light, temperature, touch, and chemical signals. These responses may be behavioral, physiological, or biochemical.
- Reproduction: Living organisms have the capacity to reproduce, either sexually or asexually, to produce offspring that inherit genetic traits from their parents.
- Adaptation: Living organisms can adapt to changes in their environment over time through evolutionary processes, such as natural selection, mutation, and genetic variation.
Based on those criteria, many in the scientific community consider a human being to be present from the moment of conception, when a single cell (zygote) is formed through the fusion of a sperm and an egg. From that point onward, the developing organism begins to meet several of the criteria for life—such as cellular organization, metabolism, response to stimuli, and potential for growth and reproduction.
Many Christians are surprised to discover that the scientific definition of life, as outlined above, closely parallels the perspective on life advocated by the modern “pro-life” movement—aside from points involving asexual reproduction and evolution. That movement asserts that life commences at conception, when a sperm fertilizes an egg, forming a zygote with unique DNA. It is argued that the zygote possesses all the genetic material necessary for human development and should therefore be regarded as a human being with inherent rights, including the right to life. That argument serves as the foundation for the movement’s opposition to abortion, viewing it as the deliberate termination of human life.
In the discussion that follows in the remainder of this section, it should be noted that no attempt is being made to pinpoint the exact moment when human life begins. Instead, the focus is solely on what the Bible says about identifying when life is present in an organism, as opposed to determining the moment an organism first acquires life.
As Bible believers, we are blessed to have a criterion revealed by God and recorded in the sacred text to guide us in determining the presence of life in an organism. That singular criterion is found in Leviticus 17:11(a), which says, “the life of the flesh is in the blood.”
While the original context of that verse concerns sacrificial law and the sanctity of blood in atonement, the wording itself presents a broader truth: “the life of the flesh is in the blood.” That statement from the Bible is not limited to animals used in offerings, nor does it depend on ritual context—it is presented as a general reality about all living flesh. It is a universal principle that is the foundation upon which the sacrificial system is built, and it remains valid beyond that specific application. In that sense, it may be rightly applied to the discussion of life in the womb.
It provides a simple yet profound statement about the relationship between life, flesh, and blood—stating that when flesh contains its own blood, it is to be considered to have life in the eyes of God. Conversely, if flesh lacks its own blood, then it is not regarded as alive by that biblical standard.
What implication does that definition of life in Leviticus—requiring the presence of blood for flesh to have life—have on the various secular interpretations about when human life begins? To answer that question, one must consider the latest research findings from Embryology and Developmental Biology, which investigate the sequential stages of human development in the womb, with special attention given to development of the blood system from zygote through embryo to early fetus.
In human development, the embryo begins forming its own circulatory system early in gestation, though the process unfolds over several weeks. Early in the third week after conception, the embryo forms three primary germ layers: the endoderm, mesoderm, and ectoderm. The mesoderm, which develops into various bodily structures including the cardiovascular system, begins differentiating to form blood vessels and blood cells. By the end of the third week and into the fourth, the embryo’s circulatory system begins to emerge. A primitive heart and blood vessels begin forming, and the yolk sac starts producing early blood cells. The circulatory system will begin to interface with the mother’s blood system through the placenta, which enables nutrient and gas exchange.
Around the fifth week of gestation, the embryo’s rudimentary circulatory system becomes more distinct and independent. Early heart tubes fuse and begin to pulse, forming a basic pumping mechanism. Circulation begins as this proto-heart sends blood through developing vessels. The liver and spleen begin to take over blood cell production from the yolk sac. By the end of the embryonic period (around weeks 7–8), the major components of the circulatory system are established. The heart is nearly fully formed, and blood vessels—arteries and veins—are well developed. At this point, the embryo becomes a fetus with its own functioning circulatory system, though it still relies on the placenta for oxygen and nutrients until birth.
While there is some variation in exact timing between individuals, all researchers agree on this key point: no blood is present in the single-cell zygote at the moment of conception. Based on the biblical criterion in Leviticus 17:11, which associates life with the presence of blood in the flesh, it would appear that the zygote, though biologically alive in a scientific sense, does not yet meet the biblical standard for being considered alive in the eyes of God.
Likewise, during the early embryonic stages, prior to the development of a functioning circulatory system, the embryo may not yet qualify as “alive” according to that specific scriptural definition. However, once the embryo develops a beating heart and circulatory system that moves its own blood through its flesh, which occurs by the end of the seventh or eighth week of pregnancy—and certainly no later than the close of the first trimester—it may rightly be considered a living human being under the biblical criterion.
At that stage, the fetus not only meets the biological definition of life but also aligns with the biblical standard of life in the flesh, and may be seen as a human being made in the image of God. As such, the fetus is deserving of respect and protection, and arguably entitled to the unalienable rights derived from that unique status.
This post is based on an article in the book Searching for the Serpent (available for download in PDF format on this website) that discusses ways in which many Christians have added interpretation to the clear meaning of Scripture.