What are you talking about?
Evolution is occuring right now, with all species.
It can happen faster if certain factors like selection have more influence, factors which apply to mankind only mildly or indirectly.
Since it doesn't stop, you could reason that either earth should become crowded exponentially with different species, or, that a niche can hold only a certain amount of species. Which is the case here. To my knowledge, the neanderthaler was the last homo that could rival our intellectual might. That was about 25000 years ago. (I may be wrong , in fact, I encourage you to look up Wikipedia)
You could as well ask yourself:
Why did all the cool giant animals die out (Giant Wombat, Cavelion, Canis Dirus etc, Giant Sloth, Titanic Snakes... pretty much every animal was more awesome back then)? Where is the link, for instance a nearly gigantic sloth? How come even one dinosaur didn't survive? Why isn't there a small mammoth or a half-mamooth half-elefant alive?
It doesn't work like that.
Also, we DO have some nice relatives, namely Bonobos, Gorillas etc.
What's wrong with them?