That question will be the impetus for endless debate and consternation for the next few generations. We stumbled through the last century searching for ways to distinguish ourselves from apes. And we did pretty well until "reality TV" came along and exposed our penchant for fit survivors and puffy chest mating games.
Today, with accelerated advances in genetics, nanotechnology, and robotics, the quest for essential humanity shifts to a new front. We concern ourselves less with the puzzle of how we gained our humanity and worry more about losing it.
Within the next 10 to 20 years, we can anticipate the evolving convergence of humans and machines. Computing will disappear as we know it. Data will flow directly to our retinas from implanted eye screens, making laptops, cell phones, and palm devices wholly redundant. We will have wireless access to high bandwidth all the time. Web sites will morph into real-time environments, allowing us to share experiences with invited others. Jump ahead another two decades and we'll flood our brains with nanobots that will serve as even more sophisticated communicators and memory banks.
Nonbiological thinking will be billions of times more powerful than biological thinking. Children today receive inoculation shots before entering kindergarten; by 2035 they may be required to receive an infusion of intelligent nanobots giving them all the information they will need to know, making school books a vestige of the past. Though my prognoses may be off, the integration of human and machine intelligence will be intimate. Count on it.