I disagree on so many points of HG Wells assumptions im not sure where to start.
Now he comes from an era where Eugenics was one of the big themes of speculation.
Me, personally, I dont even think Eugenics is possible (whether its on purpose or whether its bound to happen)
For one human beings are tool makers.
The human hand will remain pretty much the same, but what's inside a human's hand will change.
Instead of say house painters evolving longer legs, we create ladders for them to stand on. If a group of people develop diabetes, guess what? we invent insulin shots.
Many, in not all the problems other species overcome during millions of years by growing tusks,hair, scales, flippers, taller, shorter, or any other myriad of evolutionary tools.. We solve all this with inventiveness and knowledge. And the limits of knowledge practically don't exist, and the limits of our technology the same. So nature or ourselves (maybe the same thing) throws a problem at us, we solve it using tools. Where can natural selection even enter in to this? I would say it doesn't, and it can't.
Add to that people generally breed with whomever they want and for any reason they want, and people even marry people that are sterile or adopt or die after giving birth, or any other number of things. And there is no basic outline for why people pick certain mates, and it generally has nothing to do with 'the fittest'. I really dont see the human race as splitting apart so much as coming together to become more homogenized. Our technologies will grow at a rapid pace and in fact make survival of the fittest moot. Of course when we really start to make tools that create themselves and think for themselves well the landscape will change drastically.