Second Genesis — Donald Moffitt

Many centuries ago, an alien race known as the Nar was able to recreate human beings from genetic code, broadcast from Earth into outer space by a beleaguered humanity. They allow a group of humans to travel millions of light years through the galaxy, in order to discover what has happened to the original occupants of planet Earth. However, none of the human participants of the expedition are prepared for what awaits them at the completion of their journey...