The Bone Labyrinth by James Rollins

time that Homo sapiens encountered the Neanderthal tribes and began interbreeding. Are you familiar with the term heterosis ?”
    Kowalski shrugged, but Monk simply crossed his arms. She suspected he knew what she meant. In fact, he was likely several steps ahead of her but was letting her take the lead.
    “Heterosis is also called hybrid vigor,” she explained. “It’s a biological phenomenon when the mating between two different species produces an offspring—or hybrid—who displays traits that are stronger than either parent alone.”
    “And your hypothesis,” Monk said, “is that the interbreeding of Neanderthal and early man produced offspring who were smarter, resulting in this uptick in ingenuity.”
    “It’s what Lena and I were exploring. Two to three percent of modern man’s genome is made up of Neanderthal genes—with the exception of most African populations, who never interbred with Neanderthals. Additionally, we don’t each carry the same bit of Neanderthal DNA. If you add those disparate parts together, the total contributes to about twenty percent of all our genes. Certainly enough to significantly alter the path of mankind. Geneticists have already determined that some of those stretches of Neanderthal DNA likely helped our migrating ancestors adjust to the northern climates of Europe, giving us more body hair and less pigmented skin, for example.”
    “But as I understand it, there’s no indication that it enhanced intelligence in any way?” Monk asked.
    “That’s correct. And my sister and I are disinclined to believe that there’s such a direct correlation.”
    Monk frowned. “Why?”
    “Because the African population of ancient man also participated in this Great Leap Forward, while having no Neanderthal DNA. Which raises the second mystery concerning this turning point in history. This change was not an isolated phenomenon, but one that occurred almost simultaneously throughout the scattered populations and tribes of the world. Spreading across Europe, Asia, and the African continent.”
    “And how do you interpret that?”
    “Our hypothesis is this Great Leap Forward was due to a mix of genetics and social engineering. We believe this global change was indeed first sparked by interbreeding, resulting in the sudden appearance of those vigorous hybrids I mentioned—unique individuals who thought and acted differently. They in turn inspired rapid social changes—in art, in rituals, in weapon design—skills that were then taught and spread globally through migration. We know from genetics that the migration patterns of early man were not one way. Not just out of Africa, but some populations—including those carrying Neanderthal genetic markers—also returned to Africa.”
    “Let me see if I’m understanding this correctly,” Monk said. “Your hypothesis is that interbreeding triggered an intuitive leap forward in a scattering of unique individuals. Then their new way of thinking and knowledge were spread wide and far.”
    “Exactly. And it’s not just our theory, but one we extrapolated from a paper published in 2013 by an Oxford University philosopher, Nick Bostrom. He wrote that it would take only a handful of super-enhanced individuals—those with a superior intelligence—to change the world through their creativity and discoveries, innovations that could be shared globally. He was writing about the future in that paper, but his theories are just as applicable to the past, to explain mankind’s Great Leap Forward fifty thousand years ago.”
    “Super-enhanced individuals?” Monk asked. “Like your theoretical hybrids?”
    “Possibly. It’s what my sister and I are exploring: what it meant to be that first generation following the union between Homo neanderthalensis and Homo sapiens . To be fifty percent Neanderthal and fifty percent modern man. The truest hybrid. We know that the number of Neanderthal genes quickly diluted out of our genome, eventually winding