That's whole mouthful of questions there... Hmm, I'll break them up in parts and try to give an answer based on my beliefs of the Buddhism Way of Life ok? First of all, I should probably stress that all my beliefs listed here are not based on the common Buddhism teachings. They are the teachings of the Dalai Lama ie the Tibetan branch of Buddhism. Ok so anyway;I should start by giving a technically occult explanation of what is reincarnation. Reincarnation is the act of coming back to this material world from the spirit world. The time sense on a material world and that of the spirit world is quite different. and so one can learn lessons much faster on a material planet than one can in the spirit. People keep coming to Earth - or to other Earths - in much the same way as one goes to school, where it is intended that one shall learn certain lessons. At the end of the school day (death) one returns home. As one works through one class, one is promoted to another class until one has learned, in theory, all that the school (this Earth) can teach (life lessons) and then one goes on to a higher grade of school, and from school to a college or university. In much the same way one comes to this Earth, and then keeps coming back to the Earth to enter different classes. When one has learned that which the Earth can teach, one moves on to a different world, just as the adolescent moves on to a higher class at school. As to what happened precisely when a person dies; I believe in this -- The astral body will travel to a place to undergo PURGATORY... This is not HELL in the strict sense, it is nothing like the one which is usually portrayed. It is more like a HALL OF MEMORIES in the astral world. There is a short stay in 'purgatory' where the soul, or Overself, sees the mistakes committed in the life just ended... This purgatory is not a punishment centre, it is not the local jail and there are no devils who gleefully prod you with red-hot toasting forks. Purgatory is merely a planet where you shed some of your conceit, some of your illusions, and where you face up to the fact that although on Earth you had loads of money, etc., and people were afraid of you, here it is quite different, you did not bring your money with you. After the said process; then one will either be reincarnated back to Earth; or evolve to the next dimension (graduates). There are nine dimensions existing, we are upon a three-dimensional world. Unfortunately, it's quite impossible to picture a fourth or fifth dimensional world to a person living in the third dimension. For example, a one-dimensional being could only exist upon a line. People in the fourth dimensional world would view us as what we view a one or two dimensional being. (like a cardboard)... there's a lot more to dimensions; but that would be too much to explain here. And then to answer your question why is there an increase in human population; I trust (from my own deduction from the readings) it's because the real truth is much more complicated than it is. There's not only ONE plane of existence; there's NINE planes of existence and the Earth is merely one of them. Let me draw you a picture... Imagine you have a school set up somewhere. Then a certain number of pupils enrol in your school, let's say 50. Two years later, the number increases to 100. Do you ask yourself as to where these pupils come from? Easy; there may be an increase in childbirths but these children may also have came from other parts of the town/city. Many of the 'spirits' or 'souls' may have stayed in the astral plane and they vary according to the degree of evolution they have reached. People do not reincarnate because of their karma, but because they want to learn something more. You don't necessarily go to college to pay somebody else, you go to college because you want to learn something.In just the same way, people come to Earth because they want to learn something. These people may have been staying in the astral planes or dwelling in some other planes. There are quite a lot of different worlds, and one will go to different worlds just as at school, you have to go from class to class or grade to grade; or transfer to a new school.