As an embryologist and the author of embryological textbooks, I can say with absolute assurance: There is no consensus among embryologists as to when an individual human life begins.
The view that gastrulation is the beginning of an individual life has been popular in Great Britain, where embryologist Lewis Wolpert has forcefully commented, “It is not birth, marriage, or death, but gastrulation which is truly the most important time in your life.”
A third group of embryologists claims that human life begins around week 24-28, when the human-specific electroencephalogram (EEG) waves are seen. This marks the physiological states necessary for consciousness. In America, we say that the loss of the EEG (i.e., flat-lining) is the end of a human life, even though other organs are still functioning. Thus, according to this view, if we are willing to accept the loss of the EEG pattern as the death of a person, such personhood would arise when the EEG pattern was established. This period of EEG acquisition is also the period where the fetus becomes viable were it to be born prematurely.
|Remember when these human beings weren’t “people”?|
Finally, there is the fifth position that finds the question about when individual human life begins to be unscientific, if not silly. One of America’s foremost biologists, Theodosius Dobzhansky, put it this way, “The wish felt by many people to pinpoint such a stage probably stems from the belief that a soul, conceived as a preternatural entity, descends upon a formerly soulless living stuff, and suddenly transforms the latter into human estate. I hope that modern theologians can accept the idea that the transformation is not sudden, but gradual.”