I don't know if it's everlasting - I doubt it, actually - but to me it's that spark you see in everyone, the life force that's larger than just our bodies - even though that's where it's housed. Animals have it too, just less of it (and some animals have more than others).

If you see someone really powerful like Miles Davis (if there's anyone else like that), you know in an instant that it's not superstition at all. But we all have some of that.

Plants and microbes, well, I don't think they have a soul in the same sense. But I could be wrong. Consciousness is something else.