It was contained in Professor Stephen Oppenheimer's excellent book, Out Of Eden. There was an explosion of human branches just after Toba and another lesser one after The Last Glacial Maximum(LGM).
BTW, he also explains why American Indians and some Europeans are the only ones who carry the "X" gene, Toba killed everyone in between and broke the link.
I've read two of his books and highly recommend both, Eden In The East and Out Of Eden.
"Professor Stephen Oppenheimer
Stephen Oppenheimer is a world-recognised expert in the synthesis of DNA studies with archaeological and other evidence to track ancient migrations. He is a member of Green College, Oxford University."
I have come to understand that major volcanic eruptions of antiquity killed mainly via tertiary effects, such as crop destruction (as opposed to blast effects, tsunamis, etc.). I have also come to believe that American Indians were descendant of immigrants from mainland China.
I wonder, would this imply that the ancient residents of China fared far better than other genetic stocks of the time?