Na verdade, são dois romances, The Genesis Quest e Second Genesis por Donald Moffat.
The Genesis Quest gets around the problems involved with intergalactic travel, namely the distance, by avoiding the traditional staple of science fiction, faster than light travel. Instead Moffitt opts for a different tactic, that of having an alien race (The Nar) assemble humans from a stream of genetic information transmitted by radio from the Milky Way Galaxy. The resulting colony of humans spend some time integrated into the Nar society before growing restless, discovering the secret of human longevity, and embarking on the seemingly impossible millennia-long mission of a physical journey back to Earth. This epic journey is made in a gigantic space-grown semi-sentient Dyson tree known as Yggdrasil.