The revival of extinct dinosaurs was the key idea in Michael Crichton's fantastically successful book and movie franchise Jurassic Park. We don't seem likely to be able to do that in real life any time soon, or perhaps ever, but it happens that active efforts to reverse more recent extinctions are not only plausible but underway. The advantage of these more recent extinctions is that we have a good chance of recovering their actual genetic code. The NY Times magazine has a nice story on the efforts underway here.
Brand became obsessed with the idea. Reviving an extinct species was exactly the kind of ambitious, interdisciplinary and slightly loopy project that appealed to him. Three weeks after his conversation with Flannery, Brand sent an email to Church and the biologist Edward O. Wilson:
Reconstructing the the DNA code of an extinct species is actually the easy part. The harder part is fabricating, editing, and achieving the reproduction of the actual physical DNA and a an egg cell from which the animal can be grown.
It should not escape our notice that the techniques developed in this quest would be readily adapted to creating modified versions of people.