Life, in the context of human development, is most commonly understood to begin at fertilization or conception—the moment when a sperm cell from the male meets and fuses with an ovum (egg cell) from the female, creating a single-cell entity called a zygote. This zygote is genetically distinct and represents the beginning of a new human organism. Human embryologists affirm that from this point, a new human life has begun, containing its entire genetic makeup and the potential to develop through successive stages into a fully developed human being. At no other stage before fertilization is there a scientifically sound point to say that life has begun. Embryos, at any stage, are considered very young humans who have retained their human identity from this inception.
There are alternative perspectives that consider other milestones such as implantation (when the embryo attaches to the uterine wall) or later developmental stages like gastrulation (about 14 days after fertilization) as significant points in human development. Additionally, philosophical, theological, and ethical viewpoints also contribute to diverse opinions about when personhood and life truly begin. However, scientifically, fertilization is the fundamental starting point of biological human life.
Thus, the predominant scientific consensus is that life begins at fertilization, where the biological process of a new, genetically unique human organism begins.
