From article...But creating human-animal chimeras—named after a monster in Greek mythology that had a lion's head, goat's body, and serpent's tail—has raised troubling questions: What new subhuman combination should be produced and for what purpose? At what point would it be considered human? And what rights, if any, should it have?
None. It shouldn't be done. Especially by those who have a 'pathological' obsession (according to Rifkin in the article).
From Article...Weissman has already created mice with brains that are about one percent human.
Later this year he may conduct another experiment where the mice have 100 percent human brains. This would be done, he said, by injecting human neurons into the brains of embryonic mice