Everything is a sanskara. What we have done in the past, past in many, many life and what you have done in past this life. That create a good luck bad luck. Good karma, bad karma. So,

you are born because of past life.

We have blood that is come from father and mother, but we have only mind which is coming from the past, sub conscious mind, that sub conscious mind what is our past? It is there.

That has selected the mother and father also.
Father and mother seed together, one father egg and I don’t know this together, How makes that and all memory how is combination, How combine?
There is because this life come when you are not rise there is no mind. only sub conscious mind force you to born good place, bad place reach place, poor place so, that make you to select born work.