Zygote —> Embryo —> fetus —> neonate —> infant —> toddler —> child —> adolescent —> adult — these are the developmental stages of a human being. These are conceptual constructions for convenience of description, NOT separate entities. You grew from a single cell to the person you are now through cell division, and all the necessary DNA to create you was always present from the first moment that the egg and sperm fused to create you. Although only a single-cell, it possesses all the unique genetic code necessary for an individual.
Human zygotes, human embryos, human fetuses — these are human. They all have the genetic constitution and epigenetic primordia characteristic of human beings. Though immature, they are complete or whole organisms. From conception onward, the human is fully programmed, and has the active ability to develop into the next mature stage of a human being.
In the infant, fetal and embryonic stages, each of us was then what we are now: a whole living member of the species Homo sapiens. Each of us developed by a gradual, unified, and self-directed process from the embryonic into and through the fetal, infant, child, and adolescent stages of human development, and into adulthood. Each of us was once an embryo, just as we were once infants, children, and adolescents. In referring to “the embryo,” or “the fetus,” we are not referring to something distinct from the human being that each of us is, but rather to a certain stage in the development of each human being.
These are not matters of opinion, conjecture, speculation or theory. Rather, they are the expression of reality as determined by scientific observation and analysis. To deny them is to lose touch with reality.
Now just because someone can look at another human being and convince themselves they’re not really a human being, doesn’t make it so. They can call it a “non-sentient creature,” or a “seed” or even a “fluffy rainbow unicorn” if they really want to, but that doesn’t change what it actually is, and a fundamental divorce from reality does not justify the death of an innocent human being.