Isn’t that kind of what Christians who believe we have a spiritual soul AND who believe in evolution kind of assume happened? Ok, NOT an alien from a space ship, but some sort of divine intervention at some point in the evolutionary history where humans had advanced enough for souls to be inserted “into the program,” so to speak. IF I was to ever think humans had this “soul” I’d assume that when God saw that humans had developed enough consciousness and reason…blah blah blah, to understand morality, he’d simply enmass endow everyone that met the criteria with a soul, mothers, fathers and children. It’s not hard to imagine once one believes there is a God who could do such a thing.
Some Christians do indeed think this way, I’m sure. Some Christians view the “soul” as an aspect of the physical person, the “mind,” which emerges from our biological existence, rather than as some other substance added into it.