I don't understand why we should accept the asumptions about the human species at the beginning of the article. The assumption that half of all human have already lived seems presumptuous.
We are a relatively young species and a rather successful one. Who's to say how long we can hang in there. Soon we will have control over our own evolution, through genetic manipulation. I have no idea how that will be used (though I'm not optimistic). Our biggest threat is our own doomsday weapons, which is unique in evolution. I guess the future is up to us.