While there is no previous example to learn from, humans must THINK of the concequences of overpopulating the Earth NOW.   Once this mistake is made, there is no going back. Only a massively destructive war will be able to kill enough people and stop the suffering and damage to Earth.  Short sighted greedy  politicians and religions  promote population growth.   On the second day in office,  Bush enforced the "gag rule" to prevent funding for family planning.  Consequently nobody is doing "the right thing" for Earth's future.       
    
The best thing one can do now is:  Promote Zero Population growth by providing birth control for everyone on Earth.   Also pre-natal care for everyone to help prevent birth defects.  
Help save Earth from the eminent destruction of Y6B At the Population Connection web site.    

Humans worry about Earth being hit by an asteroid.  Don't worry, that is the nicest thing that can happen.    We should be so lucky.   A mile sized one could destroy a small country the size of Portugal every 10 million years.  BIG ones have caused mass extinctions as frequently as 28 million years.      

 Look at any National Geographic magazine to see the damage humans can do 'in the mere blink of an astronomical eye'  in relation to the scale of time that it took for life on Earth to evolve.   World population can double in 50 years.      

Hey!  Your grand children will live in that time.  There will *never* be any more resources, gas, oil, coal, oxygen or trees than there are now, this second.  

Dig up every drop of gas and oil now, then nations will  use the  "N" word for an answer to our problems.   "Neutron bomb"  It kills people and animals and leaves the buildings intact.  The good news is that enough rats and roaches will survive to clean up the mess.     Lots of  babies now means suicide victims later.