Discussing about the existence of evil in the universe, and why God allows it, sometimes comes to our minds why would a benevolent God create a spirit for a child, conceived intentionally by evil parents to be sold or use in human sacrifices, like it actually happens in some parts of the world.
It is definitely shocking and repugnant to imagine that a God, who knows everything, would agree to concede a child to be born knowingly that it has been conceived with no love and for immediate evil purposes. Not even the old explanation that God allows freedom of choice to humans, suffices to calm our disgust, when even human laws would deny giving a car to someone who they know, will use it immediately to run over people or to be used in a terrorist activity.
However, there is nothing that expressly says in Scripture that God creates every single spirit that comes into a human embryo.
God created Adam’s spirit. He made his body out of physical matter and then blew ‘Nismat-Hayyim’ (נִשְׁמַ֣ת חַיִּ֑ים), or ‘Breath of Life’ (Genesis 2:7) in him; but when He created Eve, we are told that she was made from Adam’s body, denoting that Eve did not undergo a similar process as Adam did, but was born from an already existing human substance; and so it is with the rest of us, through sexual reproduction.
That God gave humanity the capability of reproduction, and this power is under our control, since we can choose to have or not to have intercourse, or even use artificial methods to avoid conception; it is clear that this power was given totally to our control and discretion. The power to procreate was given to humanity in Adam and Eve, and from them we inherit our human nature and our capabilities.
And since we procreate similar beings according to our kind, it is only safe to deduct that even the birth of spirits is included in this faculty.
God gave humanity the capability to reproduce other human beings, not human bodies. When babies come out of their mother’s wombs, they come a full human being, in the process of growing and maturing, but essentially, we are all born alive and full human beings, not in waiting.
It seems to be that in this capability the spirit forms itself as soon as the embryo is born (Luke 1:15). If this is correct, then the responsibility is even greater than if God would fabricate every spirit every time there is a conception on Earth. It would be up to us to carefully take care of this capability, knowing that in us resides the capability to confer life.
That would explain why the consequences of the sin of Adam are inherited, and why some of us can chose to conceive human lives, for evil purposes. This is called Traducianism.
But however it is, we know that human life can only be reproduced from us, not from any where else, not even in clonation, or in-vitro; so our responsibility is great before God, the ultimate author and sustainer of life, and we will answer for it at the Judgement Day.