Capital punishment, self-defense, warfare, justified police homicides, euthanasia, suicide: just to name the first few situations that come to mind.
"Biology" cannot offer any answers in those situations since they involve fully-grown human beings.
Indeed. Like many others who have considered the abortion question, I don't agree that a fetus is a human being: not yet. It has the *potential* to become a person when it is born: or, at the earliest, at the point of fetal "viability" at approximately the third trimester. Until then a fetus depends entirely upon the mother and her willingness to devote her womb to its care.
Just because the fetus's status as a human being is debatable (unlike the above situations) doesn't mean that's the only question involved here. The mother has rights in this situation recognized under the Constitution and continuously reaffirmed by the Supreme Court in abortion-related decisions from the past 45+ years.