As long as I wrote about the Creation vs. Evolution debate yesterday, I might as well today write about when human life begins.
The short answer is "I don't have any idea." The longer answer adds, "And neither does anyone else."
First of all, I need to clarify two definitions, well-established by past doctinal dicussions. Personhood is when a life is first able to be treated as a human being -- a real person. Ensoulment is when a life gains a human soul.
Scripturally these are not the same. In Jeremiah 1:5 we read that personhood can begin before conception (Psalm 139:15-16 seems to agree). This is not a position people know how to deal with. What does it mean for issues of contraception, abortion, and infertility treatments if in God's eyes conception is (sometimes or always) the transition to Part II of our existence?
Among other things, it means that God places little value on prenatal life. Current research estimates that as many as 70% of fertilized eggs do not implant in the uterus, and as many as 40% of pregnancies end in miscarriage (about half of those pregnancies ending so early that they would never be noticed by the parents). It is nonsensical to assert that every conception is highly valued by God.
Either God does not see value fertilized or even newly-implanted eggs as he values human life, or he is content to let about two-thirds of humanity "skip" living in This World and go straight to the World to Come. I seldom see either alternative espoused by believers.
A different set of issues is presented when we ask when ensoulment begins. Until 14 days, an embryo lacks a "primitive streak" (what becomes the spinal column) and can split into twins. Anyone claiming ensoulment begins at conception must have an explanation for how a life with a human soul can go through twinning.
To add to the confusion, what counted as "standard belief" among believers has changed over they years.
Judaism has had more consistency. Since before the first century it taught that any fetus people know about is
a life made in the image of God. Any pregnancy is thus to be cherished! The one exception is a pregnancy that endangers the mother. In that case the fetus is classified as a rodayf, a hostile persuer (still a person), whose threat must be neutralized: by surgery if possible, or by abortion if necessary.
