Hello, an7222
If you wish, I could send you a PM with some books about this subject. I will try and answer the best I can.
As I see it, you can imagine the soul as the part of the being that survives the flesh. If you consider that everything that is, in it's more elemental level, is a vibration pattern (this is sub-eletron, sub-quark level), you can consider the soul material as well, just vibrates on a pattern we have dificulty to read with our ecquipment, so far. Still, there are some evidences, here and there. Of such evidences (difference in the weight of the body imediatelly before and after death; psicographies; unknow images on films and photos, etc.), up to 97%, I believe, are not authentic. That leaves at least 3% that must be studied. Like Allan Kardec said: better reject 10 truths, than accept one lie.
Answering your other questions: the sould starts it's connection with the body in utero, and slowly goes adapting itself to the new "clothing". Such adaptation sometimes don't stop at the birth, but completes itself after a couple of months or so. But yes, a fetus alredy has a conection with a soul.
Now, animals... I don't have an opinion about that. Aty the moment, I stick with the "if they don't, what they have makes a first-class copy of one".
Hope that helps.