One of the most contested questions in history is a seemingly simple one: When does life begin? Different cultures and societies have battled to answer this question, and to date no consensus has been reached. Of course, the answer to this question has profound ethical, legal, moral, and philosophical implications. As the United States debates the merits and pitfalls of topics like embryonic stem cell research and abortion, the arguments for the beginnings of life have found themselves renewed. Along the timeline from preconception through birth and beyond, there are several stops where one group or another has drawn a line in the sand and proclaimed that life has officially begun. In the interest of providing some clarity on this issue, let us examine the rationale behind why these groups picked their points. As a reference, a textbook on developmental biology will provide some framework.

Preconception

The earliest stopping point is held by many members of the Catholic Church, with their proclamation that “every sperm is sacred.” The held rationale is that every sperm has the possibility to fertilize an egg, become implanted, and eventually grow into a human being. Since God’s charge is to go forth and procreate, any type of hindrance to that process such as the use of condoms or birth control pills are interfering with God’s plan and therefore not allowed.

Conception

The greater religious community generally view the “moment of conception” as the standard for when life begins. However, the definition of conception is subject to variability. Some take the word conception to actually mean the act of ejaculation. Others consider conception to be the process of fertilization. Still others consider the fusion of genetic material into a new set of chromosomes to be meant by conception. The problem with any of these definitions is that the process is not instantaneous. From the time of ejaculation, sperm take 7 hours before they become active and able to fertilize an egg. Once the sperm meets the egg, a chemical cascade begins and the sperm begins to bore its way through the egg, which may take up to an hour. Once the sperm actually enters the egg, it’s another 12 hours before the sperm DNA makes its way to the egg’s DNA, and then another 24 hours for the restructuring and packaging process of new chromosomes. All told, the “moment of conception” could take anywhere from 2-3 days to complete.

Gastrulation

Another argument that is raised against the “moment of conception” line of thinking is the twinning argument. Once the genetic material is completely packaged together, a new individual is created. However, for as long as 12-14 days afterward, the embryo can split into twins or more multiples. That process would create more than one individual with identical genetic material from the same moment of conception. To account for this discrepancy, some argue that life begins at gastrulation, which is when the window has closed, the embryo has implanted in the uterus, and is now committed to grow into one human being. Supporters of this theory would therefore support stem cell research, which harvests embryos that have neither the intention nor ability to be implanted into a uterus.

Week 8

The eighth week of pregnancy is a special one, because at this point the precursors to all organs have been formed. Philosophers therefore argue that with the beginnings of a brain, the fetus now has the ability to think and react, and that marks the onset of life. Opponents argue that the rudimentary nervous system is not functional at 8 weeks, and the fetus cannot process information or move in response to a stimulus, therefore not making the fetus alive.

Quickening

Those same groups which argue against the week 8 model suggest that life begins with the “quickening,” which is when the fetus begins to exhibit voluntary movement inside the womb, usually around 14-16 weeks. At this point the fetus is able to react to external stimuli, which is held as the standard for life.

Week 20

Although the fetus can move at week 14, the movements are little more than jerky reflexes. They are not driven by higher cortical functioning. Therefore, another school of thought is that life begins at week 20, when the thalamus is completely formed. The thalamus is the relay center of the brain, and helps to connect the cerebral cortex to the spinal cord and peripheral nerves.

Week 25

A sizable contingent would assert that life begins at 25 weeks. The rationale for this starting point is based on our definition of death. The definition of death is not disputed, and is considered the time when electroencephalography (EEG) activity ceases. EEG measures brain activity and must demonstrate regular wave patterns to be considered valid. Therefore, by this rule the onset of life would be the time when fetal brain activity begins to exhibit regular wave patterns, which occurs fairly consistently around week 25. Previous to that time, the EEG only shows small bursts of activity without sustained firing of neurons.

Birth

Perhaps the second-most frequently held conviction is that life begins at the time of child birth. In Jewish Talmudic Law, for example, the writing states that once the head of the child is delivered it cannot be touched and is granted equal rights to life as the mother. Other religious groups maintain that the soul is delivered to the newborn with their first breath of air.

Self-consciousness

A minor group of philosophers maintain that the criterion for human life is self-consciousness, or self-awareness, which does not occur until well into childhood. This group believes that abortion is morally equivalent to infanticide, and that both are condonable under certain circumstances. Their viewpoint is extreme, and has generally been rejected by mainstream ethicists and theologians.

While this accounting is by no means comprehensive, and perhaps oversimplifies some concepts for the purpose of clarity, let it serve as a starting point for obtaining more information. With debate on this topic wide open, and no clear answers in sight, the best hope is to understand all viewpoints and draw an informed conclusion as to when life begins.

Reference

Gilbert, Scott F. DevBio, a Companion to Developmental Biology, Eighth Edition. Sinauer Associates Inc., March 2006. Chapter 2, subsection 1.