It's hard to know how to approach the subject of what it means to be human. For a science fiction writer, it may be easier. Creators in that particular genre are limited only by their imaginations as to the plethora of aliens and creatures to which one can compare humanity. Many people only have the animals to which we can compare mankind.
So what does it mean to be human?
It could be our emotions that define us. At the drop of a hat we can go from rage to sorrow to joy and everything in between. Then again, you can easily see emotion in certain animals. I don't know enough of the science or the biology of the animal kingdom to claim which creatures experience emotions, but can't you tell when your dog is happy to see you?
In Star Trek II: The Wrath of Khan, Admiral Kirk said that Spock's soul was the most human that he had ever encountered. For those of you who know nothing about the Star Trek universe, Spock wasn't fully human. Spock was a Vulcan, coming from a race that had learned to repress emotions in favor of logical thinking. Throughout the character's history, the viewer would see glimpses of his emotional, human side, but in general, he kept that part of himself at bay.
But maybe it's not our emotions that define us as humans. Maybe Kirk was referring to Spock's self-sacrifice. Spock knew what needed to be done in order to save the lives of the ship's crew, and therefore gave up his own life to do so. "The needs of the many outweigh the needs of the few or the one." This is what his logic dictated. Then again, perhaps that does tie back to a certain emotion. Jesus said, "Greater love has no one than this, that he lay down his life for his friends" (John 15:13).
Maybe it's our flaws that make us human. Look around every day and you see countless people striving for perfection, or whatever they believe perfection to be. Immediately, physical perfection comes to mind, with so many rushing to the doctor's office or the pharmacy to find ways to stave off the signs of aging. They look in the magazine and see the people that have been listed as beautiful this month and wish so badly that they could look like that. What they don't understand is that it's their flaws that set them apart, that make them beautiful.
As a Christian, I believe that I must strive for perfection. This isn't a physical perfection, but a spiritual one. I must strive to be Christ-like. As a Christian, I believe that Christ is the very portrait of perfection, and that His example is the one that I should be following. Every day, I fail. But it's through those failures and through my flaws that He continues to love me. Without those human frailties and imperfections, His sacrifice would have been unneeded.
So which is it? Is it our emotion that makes us human? Is it our need to better ourselves? Or is it simply our ability to make use of opposable thumbs?