I see this as a top-down process meaning the soul exists first, and then our astral/mental bodies form which then incarnates a physical fetus (all controlled and designed by higher intelligences).
The process in my view can not start with man putting a collection of physical parts together and then a soul jumps in. There are multiple non-physical bodies and layers to life required for an animate experience and these can not be manufactured by putting physical parts together. It is much more than a physical device and a soul as your argument implies.
I developed my view from decades now of study of the paranormal and the teachings of various wisdom traditions.
If you hold a materialist view (only the physical plane of nature is real and the spiritual planes of nature do not exist), I am not sure what your notion of a 'soul' is.
So, in your strange world-view, anytime someone gets an organ transplant, they also get a part of the donors soul?
Is that how this works? Because transplant recipients are, basically, "a collection of physical parts put together".
At what point is the break-over from one soul to the other? How many transplanted parts would it take?
Do blood transfusions count?
And when-- exactly-- does your hypothetical pre-existing soul jump into the body? What does it do, if it jumps into a blob of, say, 30 cells? Wait around until there are enough to fully house the soul?
Or does it simply hang out in the placenta? Or perhaps it sits in the amniotic fluid, until there are enough nerve cells to "inhabit"?
What controls the jumping threshold, anyway?
And what makes a human machine any different from a similarly functioning silicon based one?