Dark Eden by Chris Beckett
Eden: a world of perpetual darkness, lit by fluorescent vegetation and headed by geothermal trees. Five hundred humans - the Family - live in an isolated valley. They are all descended from the same couple, Tommy and Angela, astronauts stranded on Eden one hundred and sixty years ago. As a result, genetic deformities and aberrations amongst the Family are commonplace. The Family is held together by the dream that one day Earth will send a rescue ship to pick them up and take them home. For teenage hunter John Redlantern, this dream is a futile delusion. He believes that the Family must branch out to survive, as the valley's food stocks are dwindling. But the only way out of the valley is a dangerous ascent over an unlit, freezing mountain that has killed every person who has tried to climb it. John's determination to escape to a better place splits the Family apart, but how much is John's plan motivated by a desire for humanity to survive on Eden and how much to appease his...