Soul Searching

This question about existence of a thing called soul has been haunting me. Are the number of souls on earth a constant or are they increasing in number? If rebirth is to be believed then how come the population of humans has been on a rise for a long time now ? And where do the new
souls come from ?

Maybe some insects and reptiles and birds and mammals found spiritual advancement thru good karma(?) and were born as humans. But I had no theory to prove the numbers of other species is decreasing to compensate our rise, till recently.

The explosive growth of humans and all their activities in land-clearing for agriculture, large-scale fishing, CO2 exhaling vehicles and industries and a variety of polluting activities has made sure we kill every other species at an unprecedented rate. The web of life has been
cut , and the rate of extinction of all species other than flourishing homo sapiens has been on a rise. Is it time to worry yet?

But rebirth has probably made sure that the souls of the members of now extinct species are reborn as humans. Proof: I can see some people have just about enough intellectual capability as dodos do (or did). Tyrannosaurus' future generations thrive in the corporate world enjoying
the cut-throat competition. Some men do pranks that would make endangered orangutans blush, and others have the fashion-sense of a red-eyed tree-frog. Many people in country where once bisons thrived and were hunted down, now pile on enough fat to look like them, even making obesity an ailment !
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For a non-satirist yet nice introduction to effects of human activities leading to environmental problems- check out daversity.com.