Embryogenesis is the name given to the process that begins with sperm bumping into an egg and ends when a fetus is formed. There are many observable stages to embryogenesis: day 1 is fertilisation, day 2 is cleavage, day 3 is compaction, day 4 is differentiation, day 5 is cavitation, and so on.

Some people believe that human life gets a soul at conception. Except for when Saint Alphonsus Liguori, in the 18th century, pulled from his derriere the idea that a fetus receives a soul around 40 days after conception, and thus abortion was acceptable within during that period.

When exactly does a blastocyst, zygote, or fetus receive a soul?

One can easily state human life begins at conception, or the soul is bestowed sometime in the first 40 days, or babies are assigned a soul at birth. To the inquisitive, rational mind the question of when is imperative. The Catholic Church will not, and arguably can not, be specific about when the soul is bestowed.

Even if Catholics fingered the soul-bestowing moment during pregnancy, the soul is a metaphysical concept, and conveniently said to be beyond scientific inspection.