Based on the facts of science, when does every new human life begin?
Per the "American Heritage Dictionary of Science," there are four defining characteristics of life: (1) growth, (2) reproduction, (3) response to stimuli, and (4) metabolism. Numerous scientific publications show that these features of life all occur during or within moments after fertilization. Thus, an embryology textbook explains that "fertilization" creates "a new combination of chromosomes that is different from that in the cells of either of the parents," and this "is the beginning of a new human being." With the exception of identical twins, once a woman conceives a pre-birth human, the genetic odds against her conceiving the same one again are greater than the number of atoms in the universe. While genetically the same, identical twins are biologically unique from each other due to epigenetic differences that affect the expression of their genes.