The Definition of a Human Being

The boys and I are reading "St. Thomas Aquinas and the Preaching Beggars" which tells of the life of Thomas Aquinas, perhaps the most learned Catholic theologian of all time. Yet in class with his professor, who would also become a saint - Albert the Great, he was very quiet. Most of the other students thought he was a little slow in the head. In fact, they called him the "dumb ox." Until one day in class, Thomas explained a difficult problem, and Albert the Great claimed that "the dumb ox's bellow would one day be heard around the world."

In a cursory search, I wasn't able to find what the problem actually was. According to the book we are reading, however, it regarded the following logic problem.
Father Albert made the following statement: "I am a person. I speak in a high-pitched voice. Therefore, a human being is a person who speaks in a high-pitched voice." He wanted his class to figure out why the statement was silly. Thomas' classmates thought it was because some people have deep voices, therefore the statement wasn't right. Thomas took a broader perspective. He responded to his classmate:

We know what a human being is. A human being is defined in the catechism. A human being, according to the catechism, is a creature made in the image and likeness of God and endowed with a soul. In short, a human being is a child of God. That is the only essential thing about him. Everything else is accidental. Whether his voice is high-pitched or low-pitched, that is accidental. The color of his skin, the color of his eyes, where he was born, or how rich his parents are - all those things are merely accidental. The only essential thing about a human being - the only thing that matters - is that he is a child of God!

I don't know if these were Thomas' exact words although it does sound like something he would say. In any event, I think that is a wonderful definition of a human being.