The idea that an embryo or fetus is biologically human but not a person runs into a serious consistency problem. Any standard proposed to exclude unborn humans from personhood must be applied evenly—and when it is, it either strips rights from some born humans we clearly regard as persons or else extends personhood to nonhuman animals we clearly do not.
Human beings who are already born vary enormously in characteristics like age, size, sex, ethnicity, intelligence, and physical or mental ability. Despite these differences, they are treated as moral equals with the same fundamental rights, including the right not to be killed. By contrast, animals such as squirrels are not treated as members of this equal-rights community. This means there must be some grounding factor that all humans share equally and that nonhumans lack.
Attempts to ground equal rights in present abilities fail. Intelligence comes in degrees and varies widely among humans. Consciousness cannot be the basis without implying that sleeping people, newborns, or those in temporary comas lose their rights. Sentience is too broad, since it would include many animals we do not treat as rights-bearing persons. Each of these criteria either excludes some humans we know have rights or includes beings we know do not.
A more coherent explanation is that equal human rights are grounded not in what someone can do at a given moment, but in what they are—their human nature. If human nature is what explains why all born humans have equal rights despite vast differences in abilities, then unborn humans, who share that same nature, must be included as well. On that understanding, affirming equal rights consistently requires recognizing that embryos are rights-bearing persons with an equal right to life.
Key Takeaways
Equal-rights consistency: Any standard used to deny embryos personhood either removes rights from some born humans or grants them to animals, making it morally incoherent.
Ability-based criteria fail: Intelligence, consciousness, and sentience cannot ground personhood without excluding infants, the disabled, or temporarily unconscious humans.
Human nature as the grounding factor: What explains equal rights among all born humans is shared human nature, not present performance or development.
Logical extension to the unborn: If human nature grounds rights for born humans, unborn humans share that same grounding and therefore possess an equal right to life.