For a technical definition of
soul, see
What happens to your soul when you die?.
When does human soul life begin?
American Standard Version, Genesis 2:
7 And Jehovah God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul.
It seems that when a fetus receives a (detached) breath from God, it becomes a living soul.
English Standard Version, Ecclesiastes 11:
5 As you do not know the way the spirit comes to the bones in the womb of a woman with child, so you do not know the work of God who makes everything.
Psalm 139:
13 For you formed my inward parts; you knitted me together in my mother’s womb. 14I praise you, for I am fearfully and wonderfully made. Wonderful are your works; my soul [H5315 nephesh] knows it very well.
Ensoulment:
In the time of Aristotle, it was widely believed that the human soul entered the forming body at 40 days (male embryos) or 90 days (female embryos), and quickening was an indication of the presence of a soul. Other religious views are that ensoulment happens at the moment of conception; or when the child takes the first breath after being born;[1][2] at the formation of the nervous system and brain; at the first detectable sign of brain activity; or when the fetus is able to survive independently of the uterus (viability).[3]
When does consciousness begin?
According to
this Scientific American article:
Consciousness requires a sophisticated network of highly interconnected components, nerve cells. Its physical substrate, the thalamo-cortical complex that provides consciousness with its highly elaborate content, begins to be in place between the 24th and 28th week of gestation.
Elizabeth was pregnant for about half a year, Luke 1:
41 When Elizabeth heard Mary’s greeting, the baby leaped in her womb, and Elizabeth was filled with the Holy Spirit.
Wiki:
Some early Christians believed that the embryo did not have a soul from conception,[11][18][19][20] and consequently, opinion was divided as to whether or not early abortion was murder or ethically equivalent to murder.[13][17]
When does the human soul begin?
It seems to be somewhere between the time of conception to the time of full-term birth. If we don't know whether a fetus has soul life, is it okay to terminate it?