I was not too sure what to expect with a thread of this name, but I see this is about “overpopulation”. That issue of population, overpopulation and demographics is very significant to the whole concept of sustainability. It is also one of extreme complexity, and many aspects are seen as sensitive and controversial.
However, to get an idea of the expressed concerns and opinions of other members, you may find it interesting to review some of what has already been said on this forum in this general area (many more related threads can be found using the “search” function):
(GarethKane):
Population & Sustainability
(Sezbet):
Population
(Metyu):
reducing consumption and land use
(Bowman):
Sustainability is a purely a Human issue
(ActionNow):
Population reduction - government petition
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These (external) links may also contain information of interest to this topic as well:
population explosion: Definition and Much More from Answers.com
World Population Statistics[List Ranked by Country Population]
Population and Environment Linkages