Enemies of the System — Brian W. Aldiss

In the far future, a group of evolved utopians stranded on an inhospitable planet are unable to resist the reemergence of the human animal

One million years in the future, the universe has become a utopia for the humans inhabiting it. Having evolved into the race homo uniformis -- “man alike throughout” -- they share a centralized nervous system and know nothing of war, disease, violence, emotion, or any of the ancient ills that plagued their ancestors. But while en route to a vacation that is light years from Earth, a small group of elite travelers find themselves marooned in the wilderness of the planet Lysenka. And they are not alone. Many millennia ago, during Earth's darker days, human colonists came to this regenerate world, and the creatures their descendants became out of necessity bear little resemblance to the uniquely civilized beings now stranded in their midst. Here, in this place far removed from the protection of uniformity, there is only one rule: Adapt -- or die.
 
One of the twentieth century's premier practitioners of the art of science fiction, Grand Master Brian W. Aldiss offers readers a startling look into the far future with a remarkable work of speculation that explores what it means to be human.