"But you are still within human limits! In order to become a master of martial arts, you must break the wall of humanity! That is the challenge!"-Kame Sen'nin (DB028)
Humans are the dominant species of planet Earth and the closest race in the Dragon Ball universe to real-world humans; us.
Humans are a diverse people with many sub-cultures. As Earth underwent many dire threats and even survived total annihalation, it's natural that humans developed a passion for combat and protecting their world, idolizing martial arts heroes like Hercule. When Groundbreaking Science was released, knowledge of chi control and advanced martial arts techniques was spread into the human knowledge and humans became more powerful as a species.