Educating women in developing nations is key to slowing population growth. Birth control AND education.
 We are on a world wide collision course as global warming, loss of wildlife habitat, increases in toxins in our water, air and soils and too many humans using too many resources....there will be a "bottleneck" where only a limited amount of species will make it through.  I wouldn't count on the billionaires; many are sociopaths as is many leaders of nations, including our own.