The thing that makes me doubt reincarnation is the fact that poultations will incrase and decrease. So what will happen to the souls that are left out when the population decreases, in limbo until a space becomes available? I doubt if you could retain any knowledge or memory after death otherwise youd think someone on this planet would remember his/her past life but mayb we travel to a new dimension when we die and this is just a test to get into a higher plain of existance. If there is a even is a soul im pretty sure itd retain nothing (or maybe a plain between life existance) but we can never tell until the day comes....