Human Life


When human life begins

“Before I formed you in the womb, I knew you.”  (Jeremiah 1:5)

‘What God knew about you before the first cells of (what is now called) your body began to develop’ is not a valid question for scientific investigation, yet the question of when human life begins certainly is.  The life of a distinct, living human organism begins at conception*—ultimately more than one organism, in the case of identical twins.

*Conception is the first step in the process of fertilization. cf. The Scientific Consensus on When a Human’s Life Begins – PubMed (

Through the application of reason, it can be shown that the organism resulting from the joining of human gamete cells is necessarily human and alive (i.e., that characterizing this organism as non-human or not alive is scientifically incorrect):

  • A fertilized egg that contains DNA inherited only from human gamete cells contains only human DNA and hence is necessarily a human organism.
  • If conditions for growth and development are maintained, the original copy of human DNA present inside the single fertilized egg is sufficient for the formation of a large, multi-cellular human body. 
  • Observed growth and development of the human organism is sufficient evidence of life (i.e., that the organism is alive).
  • Hence, a fertilized human egg that grows and develops must be scientifically regarded as continuously human and alive; a living human organism (i.e., not a non-human or non-living thing that spontaneously becomes human or becomes living; rather from the beginning classified as human life).

The fact that human life begins at conception can be problematic for those who assert an individual or institutional right to technologically manipulate or end human life in its early stages.

cf. New Danish law: human life begins at conception

Biological sex of the human body

“Male and female He created them.” (Genesis 5:2)

The Bible is not a science textbook, rather it is intended to reveal truths about God and His Creation that are outside the domain of science (i.e., knowledge that is not reducible to the scientific form of knowledge).  Genesis chapter five verse two—written in an ancient time—happens to be in accord with what world class experts in the life sciences authoritatively teach today: that humans are mammals whose 23 pairs of chromosomes are naturally inherited from one male human gamete cell (the biological father’s sperm cell) and one female human gamete cell (the biological mother’s egg cell).

cf. Dr. Allan Herbison, Professor of Neuroendocrinology, Cambridge University School of the Biological Sciences, Department of Physiology, Development and Neuroscience

Though rare accidents* can cause abnormal* genetic conditions (e.g., Intersex, Down Syndrome), the normal outcome of fertilization and development is either a 46-chromosome per cell male (‘XY-chromosomed’) body or a 46-chromosome per cell female (‘XX-chromosomed’) body, each body becoming capable of producing gamete cells respective to its own biological sex for the creation of the next generation.

*Chromosome Abnormalities Fact Sheet; National Human Genome Research Institute (National Institutes of Health)

No cells in female human bodies contain a Y-chromosome, yet all cells in male human bodies do, except approximately half of their sperm (sperm have a single chromosome). That approximately half of sperm are ‘X’ and half are ‘Y’ is the reason there are naturally about the same number of women as there are men in every generation.

In a recent article, The U.S. Centers for Disease Control and Prevention (CDC) describes “Biological factors”—specifically (genetic) chromosomal differences—as the cause of different “sex-specific disease outcomes” for men and women.

cf. Biological differences between females, males need to be considered in scientific studies; The Endocrine Society (posted by the American Association for the Advancement of Science (AAAS))

When the (Human) Right to Life begins

“Thou shalt not kill.” (Exodus 20:13)
Life ‘is always sacred and inviolable.’—Pope Francis
“We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.”—Preamble to the Declaration of Independence

The rights enumerated in the Preamble echo the original ideas of Fransisco Suarez (1548-1617) a Spanish Jesuit Philosopher and Theologian who proposed that rights originate from God and exist in a hierarchy.  When rights conflicts occur, a wise judge must prudently consider which right to elevate above others to serve the highest good (e.g., “Your right to life is a higher good than another’s pursuit of happiness that seriously endangers your life.”).  Indeed, in nations without the Right to Life, rights to liberty, property or the pursuit of happiness are often short-lived.  


Discussion or debate about Human Life can be polarizing, and it can revolve around how terms are defined.  While Catholic teaching about the Sanctity of Life is firmly and authoritatively grounded in Sacred Scripture and Sacred Tradition, the same conclusion must inescapably be drawn from the Right to Life stated in the Preamble to the Declaration of Independence:

  • According to the Preamble—inherent to which is the Founding Fathers’ declared theism (i.e., certainty of the Creator’s existence)—all fully developed human organisms (in 1776 referred to as ‘men’) are endowed by the Creator with the unalienable (certain, unchangeable) Right to Life.
  • If the Creator hypothetically does not endow a new human organism with the Right to Life at conception, then there is a hypothetical “waiting period” of unknown duration, after which the Creator certainly does endow the Right to Life.
  • Interruption or termination of the normal growth of a developing human organism therefore either
    1. Suspends or eliminates the certain (but hypothetically delayed) endowment of the Right to Life by the Creator OR
    2. Abolishes the Right to Life that had already been endowed by the Creator.
  • What the Preamble states as a Creator-endowed—and hence unalienable—Right to Life (capitalized in the original text) can in practice become a ‘privilege of life’ that is granted or not granted according to the choices of fully-developed humans.  
  • On this view, new human life has the same legal status as property—to be protected, used or discarded as the (apparent) ‘owner’ chooses.

Catholics are called to properly form our consciences in order that our choices bring about the highest good that can be achieved through licit means.  With charitable acknowledgment of the many good desires and intentions that can affect our decisions, the National Catholic Bioethics Center publishes formal ethical opinions about health care and biomedical research that are fully informed by sound science and medicine within the context of Catholic morality.