It depends on the perspective. Basically something moves from one life to another. Most groups that believe in reincarnation say that movement is due to the actions of the person during their life or maybe other lives.

Species disappear every day. There are numerous sources where the population would be coming from, but basically people are moving "up" in the list thus leading to a larger human population.

Again, most groups consider the actions of the individual or Karma. Bad actions are finally exhausted leading to reincarnation "up the ladder".

You can only come to that conclusion through inferential logic. People knowing things they shouldn't is the most common data used to infer that that they may have learned it from a past life.

Uh yeah, this is pretty tricky. Genetics are affected by the process of reincarnation. I'll to that in more detail from my perspective in the next one.

Please keep in mind that there are many beliefs and this is only from my own personal beliefs. Upon death, the human mind dissolves inward. From Gross to Subtle to Very Subtle; conscious to deep subconscious. As the energy leaves the body, the mind leaves with it and enters an intermediate state. This state is called the Bardo in Tibetan. The intermediate state is similar to a dream. After a certain amount of time, the karma of the individual directs the mind to its next life wherever that is.

Heh, I personally believe there is some truth although there's basically zero value in it. The vast majority of mediums are just people good at reading others. They ask the right questions and follow the other person's reactions. They may even believe they are speaking to the dead, but it's a ruse. From my own believes, one can pretty much guarantee that if someone really is talking to a spirit, then it's not who they think it is.

I believe so. The things that happen in our house I can't explain. It doesn't mean it is a spirit, but some of the things sure are wild.