“Popular theory for what?”
“The Great Leap Forward.” Kate recognized David’s confusion and continued before he could speak. “The Great Leap Forward is probably one of the most hotly contested aspects of evolutionary genetics. It’s a mystery, really. We know that around 50-60,000 years ago, there was a sort of ‘Big Bang’ in human intelligence. We got a lot smarter, very quickly. We just don’t know exactly how. We believe it was some kind of change in brain wiring. For the first time, humans began using complex language, creating art, making more advanced tools, solving problems—”
David stared at the wall. “I don’t see—”
Kate brushed her hair back. “Ok, let me start over. The human race is about 200,000 years old, but we have only been so called behaviorally modern humans, the really, really smart-type that took over the globe, for around 50,000 years. So 50,000 years ago, we know there were at least three other hominids — Neanderthals, Homo Floresiensis—”
“Homo flor—”
“They’re not widely known. We only recently found them. They were smaller, sort of hobbit-like humans. We’ll just say Hobbits, it’s easier. So 50,000 years ago, there’s us, the Neanderthals, Hobbits, and Denisovans. Actually there were probably a couple more hominids, but the point is there were say five or six subspecies of humans and that our branch of the human tree explodes while the others die out. We go from a few thousand to seven billion people in the span of 50,000 years and the other human subspecies go extinct. We conquer the globe while they die in caves. It’s the greatest mystery of all time, and scientists have been working on it since time began. Religion too. At the heart of the question is how we survived. What gave us such a huge evolutionary advantage? We call this transformation the Great Leap Forward, and the Toba Catastrophe Theory proposes how this great leap forward could have happened — how we became so smart while our cousins, other hominids — Neanderthals, Hobbits, etc — they all remained basically cavemen. About 70,000 years ago, a super-volcano erupted at Mount Toba, here in Indonesia. The eruption and ash as well as the resulting climate change, reduced the total human population drastically, maybe to as low as 10,000 or even less.”
“Wait, the human race was down to 10,000 people?”
“We think so. Well, the estimates aren’t exact, but we know there was a huge population reduction, and that it was marked in our subspecies. We think Neanderthals and some other hominids alive at the time might have fared better. The Hobbits were down-wind of Toba and the Neanderthals were concentrated in Europe. Africa, the Middle East, and South Asia took the brunt of the effects of the Toba eruption and that’s where we were concentrated at the time. Neanderthals were also stronger than we were and they had bigger brains; that could have given them an additional survival advantage, but we’re still sorting that out. We do know that humans got hit hard by the Toba Super Volcano. We were on the brink of extinction. That caused what population geneticists call a population bottleneck. Some researchers believe that this bottleneck caused a small group of humans to evolve, to mutate to survive. These mutations could have led to humanity’s exponential explosion in intelligence. There’s genetic evidence for it. We know that every human being on the planet is directly descended from one man who lived in Africa around 60,000 years ago — a person we geneticists call Y-Chromosomal Adam. In fact, everyone outside of Africa is descended from a small band of humans, maybe as few as 100, that left Africa about 50,000 years ago. Essentially, we’re all members of a small tribe that walked out of Africa after Toba and took over the planet. That tribe was significantly more intelligent than any other hominids in history. That’s what happened, but we don’t know how it happened. The truth is we don’t actually know how our subspecies survived Toba or how they became so much more intelligent than the other human subspecies alive at the time. It had to be some sort of change in brain wiring, but no one knows how this great leap forward occurred. It could have been due to a change in diet or a spontaneous mutation. Or it could have happened gradually. The Toba Catastrophe Theory and the population bottleneck is just one possibility, but it’s gaining followers.”
He looked down, seeming to consider this.