Yazata
Valued Senior Member
Logically reincarnation doesn't make sense.
7 billion people are alive now.
When there was only 10 million people on Earth, where were the other 6,990,000,000 'souls' that are in use today?
The traditional Indian answer to that one is that most rebirths aren't human rebirths. I'm most familiar with the earlier Buddhists and will use them as my example. Buddhists say that being born as a human is very auspicious and not something to be wasted, because enlightenment is easier to attain as a human than it is from most other states of rebirth.
The Buddhists traditionally say that all sentient beings are reborn according to their karma. That includes all the animals, from insects to us, and it's common and routine to move from one to the other. Not only that, they also traditionally believed that there are an unlimited and potentially infinite number of other world systems out there, all with their own loads of inhabitants.
And perhaps most significantly, the Buddhists gave everything a 'vertical dimension', imagining a whole hierarchy of multiple heavens and hells, representing ontological states of being analogous to the various psychological states that individuals can attain (or descend to). The heavens are kind of ontological analogues to the various jhanas of meditation for example. Traditionally, rebirths can (and typically do) occur in these higher and lower 'planes' as well as on this earthly one.
Significantly, it's possible for human beings to be reborn as gods in heaven, and given the unlimited time-scales of Buddhist cosmology, all of us have been gods at some point. (Traditional Buddhist gods are mortal, albeit extremely long-lived.) All of us have been hell-demons too. That's the attitude that Buddhism tries to impart: when we see an insect walking along, we should think "Been there, done that."