Humans will eventually become extinct. People treat that as a radical thing to say. But the fossil record shows us that everything eventually becomes extinct. It depends what "eventually" means. But the idea that were going to be around for the rest of global history. . . I don't think there's any scientist who would suggest that is true. It could be millions of years from now. We may leave descendants that are humanlike.
It's the old idea that the process of evolution is some push in the direction of greater complexity--in particular greater intellectual complexity. In one twig of the tree of life, namely ours, having a big brain happened to have advantages. But that's just what worked for a particular species of primate 5 to 7 million years ago.
I think there will come a time when civilized people will look back in horror on our generation and the ones that have preceded it; the idea that we should eat other living things running around on four legs, that we should raise them just for the purpose of killing them! The people of the future will say 'meat-eaters' in disgust and regard us in the same way that we regard cannibals and cannibalism.