The Great Wall of China. A walk on the moon. Genome sequencing. How did we humans, who share almost all of our DNA with chimpanzees, end up doing all that, while they ended up pretty much where they started?
Some scientists will tell you it was language, or tools, or brainpower.
Another group of researchers has come up with a new and surprising theory — that something else put us on the road to success. They say it has to do with how we raised our kids.
This new theory claims that sharing — first of food and child care, then later of feelings and intentions — was the original secret of our species' success. Without it, we might have occasionally hunted in a group like other apes, but human civilization requires more than occasional male bonding.
So why did we evolve this ability to be so ultrasocial and ultrasharing? Why not chimps?
See what these scientists think may have happened.