From Dragon Ball Encyclopedia
|Average Height||Roughly 5 - 6 feet|
Humans (sometimes referred to as just Earthlings) are the main inhabitants of planet Earth in Dragon Ball. They share the planet with other intelligent lifeforms, including anthropomorphic animals. In fact, they are lead by an anthropomorphic dog named King Furry.
With the exception of the uncommon hair colors and occasionally odd features (ranging from longer lifespans to werewolfism), Dragon Ball humans are identical to their real-life counterparts. Humans in Dragon Ball seem to be able to utilize or be affected by certain elements of magic. Toriyama himself has admitted to lack of forethought or planning when it comes to the details of Dragon Ball's story, which accounts for some of the strange occurrences.
Humans have a large military, which has appeared through out the series, mostly consisting of ground troops, tanks, fighter jets, and large naval ships. Earth's military usually appears when attempting to defeat many of the villains that cause massive damage to the Earth (examples being Cell and Djinn Boo), but are always easily wiped out without causing any form of damage to the super villains. It could be assumed that large scale wars have taken place in the Dragon World, much like they have in the real world. However, since the Dragon World is united into a single, global monarchy, it is unknown what purpose the military serves when villains are not terrorizing the Earth that police cannot handle. It may be possible that The Great Demon King Piccolo's original appearance some 300 years before the events of Dragon Ball encouraged the then-king to create a military for just such purposes.
When compared to other races of Dragon Ball, average humans are significantly weak. It is said that a single Saiyan infant would be capable of destroying the average human population on its own (in fact, Son Goku was sent as an infant to Earth with that exact purpose). The only "normal" human whose power level was reported was a farmer, who Raditz said had a power level of 5. Though his level is probably representative of normal humans, there exist some particularly powerful humans, such as Muten-Rôshi, Tenshinhan, Olibu, Kuririn, Chiaotzu, Yamcha, Tao, Master Shen, Yajirobe and Oob. Most of these human fighters are also Z Fighters. These few humans have learned to use ki and are among the strongest beings in the universe. Even with such abilities, this select group of humans are still considerably weaker than many aliens with the same ki-manipulation abilities. As stated in the manga, it's possible for any human to use their ki and gain powers like the Z Fighters. For example, Son Gohan easily teaches Videl how to use ki to fly.
Mr. Satan is considered to be the strongest of the non-powerful humans, but in reality pales in comparison to humans like Kuririn and Yamcha, who possess a lot more power. However, this is mostly due to the fact that these humans were granted more opportunities to increase their strength; for example, Kuririn had his potential unlocked artificially by Guru and was trained by Muten-Rôshi, and Yamcha trained under King Kai. All of the human Z-Fighters climbed Karin Tower and trained under Kami, all things that Mr. Satan never had the chance to do.
 Dragon Ball Online
It is explained in Dragon Ball Online that after Son Gohan writes a book in 800 Age that unveils the secrets of ki and martial arts, fighting becomes incredibly popular amongst the Humans, thus ushering in a new dawn of warrior Humans. Kuririn and Tenshinhan creates schools to train Human warriors, and even Son Goten and Trunks start a sword school.
This of course greatly aids the Humans when Miira attacks nearly a millenia later, allowing the Humans to push forward a resistance against the being, thus the events of the game.
Humans are also capable of using the Super Saiyan transformation in this game, but only if granted by the Dragon Balls.