In rebirth, the soul doesn't exist. If it does, it does not exist in the same way you are thinking of. Since in Buddhism, the "self" is seen as an illusion and actually non-existant, then a "soul" which contains the individual essence or spirit of a person would not make sense. Rather, what is passed on from any living being is its energy.

For example, say somebody dies, their body is decomposed which releases energy into the universe's pool of energy, which everything is made out of. When a life is conceived, the energy manifests to create the being.

Rebirth isnt like, you die and your soul is then born again as a cow or another person or whatever, somehow. Its more like when you light one candle with another. No actual substance is transferred between them, but one is the cause of the other. Or like a seed that turns into a sprout... The sprout is not the same as the seed, but without the seed the sprout could not have come into existence.

The population problem is not actually a problem. Since the energy for new life does not necessarily need to come from human life, the fact that the population is growing actually coincides with this theory in a way. As the population grows, plants, trees and animals perish, which are all also composed of energy which returns to the universe.

I agree with you about how we shouldnt be focusing on death anyway. I mean, in a way we experience death everyday. Think about yourself 10 years ago... Where is that person now? You have completely changed since then, who you were 10 years ago doesnt exist anymore, and will never exist again. Essentially that person is dead. 10 years from now, we will be completely different to how we are now and us as we know ourselves now wont exist anymore.

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