I think that idea of transmigration of souls is a most viable one and I have reasons to believe in it myself. My only problem had been, and still is from a highly personal human perspective, is the limited human phenomenological understanding of time.
What I mean by this is that there is much evidence to postulate that linear time is an illusion, and if this is the case then the linear understanding of a transmigration as it were might be a little flawed.
Linear postulates of time have as a tendency the tendency to create hierarchy; that is I am this person now because of what I did and I will be this person in the future because of what I am doing now (I was bad before but now I am ascending towards become enlightened and better). But what if all time is a 'spacious present' as I like to call it?
In which case there is no migration or separation per se, all exists now, and the separation between one self and the other (or the movement of the soul from one body to another as it were) is an illusion brought about by a limited 3 dimensional perspective.
Sorry not trying to be cryptic, just trying to expand on the ideas of the article by asking the reader to contemplate the idea that all might be far more complex than one might suppose at first, and that there might not be any such thing as evolution but that all exists now in an ever expanding present point.