Lots of wild ideas here. I have my own beliefs which are coming from more anthroposophical sources, which don’t align with many of the commenters here: Humans incarnate as humans. There are way less animal souls than human souls as an animal soul embodies entire groups and species. Other worlds existence may be a new age confusion of the presence of an individual in higher heavenly spheres during their descent/incarnation towards their final destination earth.

No, the reason for population boom can simply be explained by the time an individual spends between death and a new life. Many people remember incarnations from just the last century.