10/29 SPECIATION

I love speciation, I have always enjoyed learning more about it in high school and ecology last year. Speciation can be pretty confusing, my three questions are the following:

1. For genealogical species, how does that animal know that this stranger shares their genes with them, do they not confuse some  other species who may look alike?

2. Will post-zygotic isolation grow to be more fitting and advantageous?

3. It almost seems impossible to determine every species of animals in the world because there are so many, how did they keep track of species already identified especially without the technology we have today?